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Anna CIPRIANI
Professore Associato
Dipartimento di Scienze Chimiche e Geologiche - Sede Dipartimento di Scienze Chimiche e Geologiche
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Pubblicazioni
2024
- Abrupt and persistent shutdown of the thermohaline forcing during MIS5e in the Adriatic Sea: Insights from shallow-water sapropel sediments
[Articolo su rivista]
Tesi, T.; Asioli, A.; Massara, E. P.; Montagna, P.; Pellegrini, C.; Nogarotto, A.; Cipriani, A.; Piva, A.; Muschitiello, F.; Rovere, M.; Viaggi, P.; Trincardi, F.
abstract
2024
- The Messinian salinity crisis onset in Albania: An integrated approach by bio-magnetostratigraphy and rock magnetic analyses
[Articolo su rivista]
Bigi, D.; Lugli, S.; Manzi, V.; Roveri, M.; Pashko, P.; Milushi, I.; Muttoni, G.; Turco, E.; Cipriani, A.; Lugli, F.
abstract
We carried out an integrated stratigraphic study aiming the identification of the onset of the Messinian salinity crisis (MSC) in the Peri-Adriatic Depression, a region forming the northern front of the Albanides fold-and-thrust belt. The onset was identified in the Kavaje area within an interval of euxinic shales representing a time-equivalent deposit of the Primary Lower Gypsum of stage 1 of the MSC, recognized elsewhere in the Mediterranean realm (CIESM, 2008). This interpretation is supported by the integration of magneto-stratigraphic (base of Gilbert chron) and bio-stratigraphic data (last influx of T. multiloba; last occurrence of foraminifera) calibrated with precessional cyclicity recognized in the pre-evaporitic sediments by rock magnetic analyses. Detailed sedimentological observations revealed that the overlying Gips-Sharrë Gypsum unit consists of chaotic and clastic evaporites floored by a regional-scale erosional surface. Their 87Sr/86Sr values (0.708937 to 0.708967) are typical of stages 1–2 of the MSC. Consequently, their assignment to the Resedimented Lower Gypsum unit is here proposed. The halite deposits, that have been intercepted by boreholes above the Gips-Sharrë Gypsum unit, have been also framed in the RLG. Our results confirm the applicability of the MSC 3-stage model (CIESM, 2008) also in the eastern side of the Adriatic Sea.
2023
- Characterisation of Conventional 87Sr/86Sr Isotope Ratios in Cement, Limestone and Slate Reference Materials Based on an Interlaboratory Comparison Study
[Articolo su rivista]
Kazlagic, A.; Rosner, M.; Cipriani, A.; Frick, D. A.; Glodny, J.; Hoffmann, E. J.; Hora, J. M.; Irrgeher, J.; Lugli, F.; Magna, T.; Meisel, T. C.; Meixner, A.; Possolo, A.; Pramann, A.; Pribil, M. J.; Prohaska, T.; Retzmann, A.; Rienitz, O.; Rutherford, D.; Paula-Santos, G. M.; Tatzel, M.; Widhalm, S.; Willbold, M.; Zuliani, T.; Vogl, J.
abstract
An interlaboratory comparison (ILC) was organised to characterise 87Sr/86Sr isotope ratios in geological and industrial reference materials by applying the so-called conventional method for determining 87Sr/86Sr isotope ratios. Four cements (VDZ 100a, VDZ 200a, VDZ 300a, IAG OPC-1), one limestone (IAG CGL ML-3) and one slate (IAG OU-6) reference materials were selected, covering a wide range of naturally occurring Sr isotopic signatures. Thirteen laboratories received aliquots of these six reference materials together with a detailed technical protocol. The consensus values for the six reference materials and their associated measurement uncertainties were obtained by applying a Gaussian, linear mixed effects model fitted to all the measurement results. By combining the consensus values and their uncertainties with an uncertainty contribution for potential heterogeneity, reference values ranging from 0.708134 mol mol-1 to 0.729778 mol mol-1 were obtained with relative expanded uncertainties of ≤ 0.007 %. This study represents an ILC on conventional 87Sr/86Sr isotope ratios, within which metrological principles were considered and the compatibility of measurement results obtained by MC-ICP-MS and by MC-TIMS is demonstrated. The materials characterised in this study can be used as reference materials for validation and quality control purposes and to estimate measurement uncertainties in conventional 87Sr/86Sr isotope ratio measurement.
2023
- Characterization and Provenance of Carbonate Rocks for Quicklime and Dololime Production in Twin-Shaft Regenerative Kilns from the Arabian Peninsula and Neighboring Countries
[Articolo su rivista]
Vola, Gabriele; Ardit, Matteo; Frijia, Gianluca; Di Benedetto, Francesco; Fornasier, Flavio; Lugli, Federico; Natali, Claudio; Sarandrea, Luca; Schmitt, Katharina Elena; Cipriani, Anna
abstract
2023
- Geochemical investigation of the mixed Máriahalom vertebrate fauna at the Paleogene–Neogene boundary in the Central Paratethys: environmental conditions and age constrain
[Articolo su rivista]
Kocsis, L.; Rabi, M.; Ulianov, A.; Cipriani, A.; Farkas, I. M.; Botfalvai, G.
abstract
The fossil vertebrate fauna of Máriahalom contains remains from a wide range of ecologies including terrestrial and aquatic mammals, crocodiles, sharks, and rays among others. All these were found mixed in mollusc-rich, shallow water, coastal deposits. The aim of the study is to trace the origin of the fossils using their rare earth element (REE) content and their respective ecology with stable oxygen isotopic compositions. In addition, marine vertebrates and calcareous marine fossils were analysed for their Sr isotope composition to provide a new age estimate for the locality. The REE content and their distribution in the fossils indicate similar early diagenetic environments and possible contemporaneous fossilization for the entire vertebrate assemblage. Reworked fossils of significantly different age can be excluded. The enamel/enameloid-derived phosphate oxygen isotope composition of selected fossil taxa fit well with previously inferred habitats that include marine, brackish, and terrestrial environments. Notably, the stem-pinniped Potamotherium valletoni is best interpreted as freshwater dweller instead of marine, consistent with the sedimentology of other occurrences. Our novel 87Sr/86Sr data suggest an Aquitanian age (21.4 ± 0.5 Ma) for the Máriahalom site that is younger than the previously proposed Late Oligocene age based on biostratigraphy (MP28–30 European Mammal Paleogene Reference Levels). An Aquitanian age raises the possibility that the index fossil taxon, the anthracothere mammal Microbunodon minimum, may have vanished earlier in Western Europe than in the Central Paratethys region.
2023
- La produzione metallurgica nel sito del Bronzo Medio e Recente di Solarolo-via Ordiere (Ravenna): aspetti della tecnologia e provenienza del rame
[Articolo su rivista]
Severi, Simone; Cattani, Maurizio; Lugli, Federico; Cipriani, Anna; Cavazzuti, Claudio
abstract
2023
- Machine learning-based Sr isoscape of southern Sardinia: A tool for bio-geographic studies at the Phoenician-Punic site of Nora
[Articolo su rivista]
Gigante, Melania; Mazzariol, Alessandro; Bonetto, Jacopo; Armaroli, Elena; Cipriani, Anna; Lugli, Federico
abstract
Since prehistoric times, the island of Sardinia—in the western Mediterranean—has played a leading role in the dynamics of human population and mobility, in the circulation of raw materials and artefacts, idioms and customs, of technologies and ideas that have enriched the biological, linguistic and cultural heritage of local groups. For the Phoenician and Punic periods (from the 9th to the 3rd centuries BCE), the ancient site of Nora—in southern Sardinia—represents an emblematic case in the study of migratory phenomena that occurred on the Island from the Iron Age until the Roman conquest. Despite the importance of exploring (and characterising) such movements from a wider bio-cultural perspective, the application of bio-geochemical tools for geographical provenance to the ancient skeletal populations of Sardinia is yet scarce. The present work is the first step towards filling this gap with the development of the first isoscape of southern Sardinia using new bioavailable Sr isotope data and a machine-learning approach. From a geolithological point of view, Sardinia is rather heterogeneous and requires detailed studies to correctly assess the distribution of the isotopic signature of bioavailable Sr. The random forest model employed here to construct the Sr isoscape uses several external environmental and geological variables. The most important predictors are related to age and bedrock type, with additional input from local soil properties. A 10-fold cross-validation gives a mean square error of 0.0008 and an R-squared of 0.81, so the model correctly predicts the 87Sr/86Sr ratio of unknown areas. By using a Bayesian provenance assignment workflow, we tested the isoscape here produced to determine the geographic origin and the mobility of archaeological and modern fauna collected from the Phoenician-Punic site of Nora and the surrounding Pula Plain. Our results indicate that archaeological sheep and goats (87Sr/86Sr < 0.7090) are compatible with areas close to Nora and Pula Plain, in agreement with archaeological evidence of pastoralism in those areas. Modern wild and domesticated fauna (87Sr/86Sr > 0.7090) show compatibility with several natural and anthropogenic locations in southern Sardinia, as expected based on modern species distribution data. Finally, we discuss the large Sr isotopic variability of the Nora baseline, where human mobility studies of human cremated and inhumed individuals are currently underway.
2023
- New insights on Celtic migration in Hungary and Italy through the analysis of non-metric dental traits
[Articolo su rivista]
Piccirilli, E.; Sorrentino, R.; Lugli, F.; Bortolini, E.; Silvestrini, S.; Cavazzuti, C.; Conti, S.; Czifra, S.; Gyenesei, K.; Kohler, K.; Tanko, K.; Vazzana, A.; Jerem, E.; Cipriani, A.; Gottarelli, A.; Belcastro, M. G.; Hajdu, T.; Benazzi, S.
abstract
The Iron Age is characterized by an extended interweaving of movements by Celts in Europe. Several waves of Celts from Western and Central Europe migrated southeast and west from the core area of the La Téne culture (between Bourgogne and Bohemia). Through the analysis of non-metric dental traits, this work aims to understand the biological relationship among Celtic groups arrived in Italy and the Carpathian Basin, as well as between local populations and Celtic newcomers. A total of 10 non-metric dental traits were analyzed to evaluate biological affinities among Celts (Sopron-Krautacker and Pilismarót-Basaharc) and Scythians-related populations from Hungary (Tápiószele), Celts from continental Europe (Switzerland and Austria), two Iron Age Etruscan-Celtic sites from northern Italy (Monterenzio Vecchio and Monte Bibele), 13 Iron Age central-southern Italic necropolises, and the northern Italian Bronze Age necropolis of Scalvinetto. Strontium isotopes were measured on individuals from the necropolis of Monte Bibele to infer their local or non-local origin. Results highlight the existence of statistically significant differences between Celts and autochthonous Italian groups. Celtic groups from Hungary and Italy (i.e., non-local individuals of Monterenzio Vecchio and Monte Bibele) share a similar biological background, supporting the historical records mentioning a common origin for Celts migrated to the eastern and southern borders of today’s Europe. The presence of a supposed Steppean ancestry both in Celts from Hungary and Celts from northern Italy corroborates the hypothesis of the existence of a westward migration of individuals and genes from the Steppe towards northern Italy during the Bronze and Iron Age, which contributed to the biological variability of pre-Celtic and later Celtic populations, respectively. Conversely, individuals from central-southern Italy show an autochthonous pre-Iron Age background. Lastly, this work supports the existence of Celtic migratory routes in northern Italy, as shown by biological and cultural admixture between Celts and Italics living together.
2023
- Origin of a carbonate-bearing fluorapatite from Tertiary volcanics of the Veneto Volcanic Province, Italy
[Articolo su rivista]
Cipriani, A.; Giovanardi, T.; Mazzucchelli, M.; Lugli, F.; Sforna, M. C.; Gualtieri, A. F.; Di Giuseppe, D.; Gaeta, M.; Brunelli, D.
abstract
We present chemical and mineralogical data on a megacryst of a unique carbonate-bearing fluorapatite from altered Tertiary volcanics of the Veneto Volcanic Province (VVP) in the western Lessini Mountain range (Veneto, northern Italy). The cm-sized specimen was identified and characterized by scanning electron microscope (SEM), X-ray powder diffraction (XRPD), micro-Raman spectroscopy and electron probe microanalyses. Major and trace elements of the carbonate-bearing fluorapatite are consistent with the crystallization at depth from a nelsonitic melt or an evolved alkaline melt derived from a mantle source metasomatized by carbonate-rich fluids. The Sr and Nd isotopic composition fits with the lavas and xenoliths from the VVP showing a DM-HIMU affinity with addition of a crustal, possibly carbonate, component. Our data are in agreement with a recent geodynamic model for the hybridization of the VVP mantle triggered by breakdown of carbonates within the subducting Tethyan oceanic slab. Cronstedtite, chabazite-Ca, calcite associated with reaction rims of amphibole and secondary carbonate-rich fluorapatite within the megacryst originated from low temperature hydrothermal alteration of the volcanics. Cronstedtite is the first occurrence in the VVP area.
2022
- A strontium isoscape of Italy for provenance studies
[Articolo su rivista]
Lugli, F.; Cipriani, A.; Bruno, L.; Ronchetti, F.; Cavazzuti, C.; Benazzi, S.
abstract
We present a novel database of biological and geological 87Sr/86Sr values (n = 1920) from Italy, using literature data and newly analysed samples, for provenance purposes. We collected both bioavailable and non-bioavailable (i.e. rocks and bulk soils) data to attain a broader view of the Sr isotope variability of the Italian territory. These data were used to build isotope variability maps, namely isoscapes, through Kriging interpolations. We employed two different Kriging models, namely Ordinary Kriging and Universal Kriging, with a geolithological map of Italy categorized in isotope classes as external predictor. Model performances were evaluated through a 10-fold cross validation, yielding accurate 87Sr/86Sr predictions with root mean squared errors (RMSE) ranging between 0.0020 and 0.0024, dependent on the Kriging model and the sample class. Overall, the produced maps highlight a heterogeneous distribution of the 87Sr/86Sr across Italy, with the highest radiogenic values (>0.71) mainly localized in three areas, namely the Alps (Northern Italy), the Tuscany/Latium (Central Italy) and Calabria/Sicily (Southern Italy) magmatic/metamorphic terrains. The rest of the peninsula is characterized by values ranging between 0.707 and 0.710, mostly linked to sedimentary geological units of mixed nature. Finally, we took advantage of the case study of Fratta Polesine, to underscore the importance of choosing appropriate samples when building the local isoscape and of exploring different end-members when interpreting the local Sr isotope variability in mobility and provenance studies. Our user-friendly maps and database are freely accessible through the Geonode platform and will be updated over time to offer a state-of-the-art reference in mobility and provenance studies across the Italian landscape.
2022
- Age, geochemistry and mantle source of the Alto Diamantino basalts: Insights on NW Paraná Magmatic Province
[Articolo su rivista]
Giovanardi, Tommaso; da Costa, Paulo Cesar Corrêa; Girardi, Vicente A. V.; Weska, Ricardo K.; Vasconcelos, Paulo M.; Thiede, David S.; Mazzucchelli, Maurizio; Cipriani, Anna
abstract
The Paranà-Etendeka is one of the largest and most thoroughly investigated large igneous provinces in the world formed in a very narrow time-range (i.e., 1.6–3.0 Ma) between 135 and 132 Ma. The South American portion of this province, i.e. the Paranà Magmatic Province, is mainly characterized by a mafic magmatism of coeval low and high-Ti magmatic terms. This bimodal activity has been explained by different degrees of melting of a homogenous mantle source or by plume activity and metasomatism of the sub-continental mantle. Despite the large body of literature, the true origin of the mantle source and processes leading to this bimodal magmatism are still debated.
In this work, we present the first geochronological, geochemical and isotopic data of basalts from Alto Diamantino (southern Mato Grosso, Brazil). These basalts have tholeiitic affinity and can also be classified in two different suites based on TiO2 content (L-Ti < 3 wt%; H-Ti > 3 wt%) and Ti/Y (450 ppm), similarly to other volcanics from the Paran´a Magmatic Province. Other geochemical parameters as Zr/Y and Nb/Yb ratios range from 3.78 to 8.60 and from 3.82 to 8.31, respectively. The L-Ti and H-Ti series have significant geochemical similarities, including 87Sr/86Sr ratios, with the Ribeira and Pitanga basalts of the Paran´a Magmatic Province, respectively. The 40Ar/39Ar ages of the two series are statistically equivalent ranging between 134.4 ± 1.6 and 132.9 ± 2.0 Ma. Our data suggest that the Alto Diamantino basalts constitute the northwestern most expression of the Paranà Magmatic Province. Sr and Nd isotope ratios suggest that the original source of the Alto Diamantino basalts was a EM-I metasomatized mantle characterized by small amounts of different components (DMM and EM-II). Positive Ba and lack of Pb anomalies, together with K/Rb ratio, indicate the presence of amphibole in the mantle source of the Alto Diamantino basalts. Th/Nb and TiO2/Yb ratios suggests that the compositional difference between the L-Ti and H-Ti basalts could be explained by different degree of melting at different depths of a heterogeneously metasomatized mantle source. The H-Ti group of basalts is compatible with low degrees of partial melting at depth while the L-Ti suite records larger degrees of melting. The metasomatic event occurred after the Mesoproterozoic, possibly during the Neoproterozoic formation of the Gondwana supercontinent.
2022
- Mantle Xenoliths from Huanul Volcano (Central-West Argentina): A Poorly Depleted Mantle Source under Southern Payenia
[Articolo su rivista]
Bertotto, Gustavo W.; Mazzucchelli, Maurizio; Giovanardi, Tommaso; Conceiçao, Rommulo V.; Zanetti, Alberto; Schilling, Manuel E.; Bernardi, Mauro I.; Ponce, Alexis D.; Jalowitzki, Tiago; Gervasoni, Fernanda; Cipriani, Anna
abstract
Huanul is a shield volcano with several lava flows hosting mantle xenoliths erupted during the Pleistocene (0.84 ± 0.05 Ma). It is located in the southern part of the Payenia Volcanic Province, which is among the largest Neogene-Quaternary volcanic provinces of South America. The vol-canism here has been ascribed as the northernmost expression of the back-arc volcanism of the Andean Southern Volcanic Zone. We present the first petrographic and mineral chemistry study of mantle xenoliths collected from Huanul lavas with the aim of reconstructing directly the mantle source of the Payenia Volcanic Province. Xenoliths are commonly small (<5 cm in radius) but scarcely crossed by basaltic veins. All xenoliths have a fertile lherzolitic modal composition and are equilibrated in the spinel-facies. Most of them exhibit an almost primitive-mantle geochemical affinity, characterized by slightly depleted clinopyroxene REE patterns reproducible by partial melting degrees between 0 and 4% of a PM source. Geothermobarometric P-T estimates of cli-nopyroxene-orthopyroxene couples form a linear trend between 10 and 24 kbar with constant increase of T from 814 to 1170 °C along a 50–60 mW/m2 geotherm. Evidences of interaction with the host basalts occur as spongy textures in clinopyroxene and reacted spinel, which tend to became more restitic in composition and show chromatographic or complete overprinting of the trace element compositions. The presence of plagioclase and calculated P-T values constrain this melt/rock reaction process between 6 and 14 kbar, during magma ascent, and fit the mantle ad-iabat model. Calculated melts in equilibrium with the primary clinopyroxenes do not fit the composition of the host basalt and, together with the geothermobarometric estimations, point to an asthenospheric mantle source for the magmatism in southern Payenia. The PM geochemical affinity of the xenoliths of Huanul is an extremely rare finding in the South America lithospheric mantle, which is commonly extensively refertilized by subduction-derived melts.
2022
- Open-closed-open paleofluid system conditions recorded in the tectonic vein networks of the Parmelan anticline (Bornes Massif, France)
[Articolo su rivista]
Berio, Luigi R.; Mittempergher, Silvia; Storti, Fabrizio; Bernasconi, Stefano M.; Cipriani, Anna; Lugli, Federico; Balsamo, Fabrizio
abstract
2022
- Palaeoenvironmental setting and depositional model of upper Messinian microbialites of the Salento Peninsula (Southern Italy): A central Mediterranean Terminal Carbonate Complex
[Articolo su rivista]
Vescogni, A.; Guido, A.; Cipriani, A.; Gennari, R.; Lugli, F.; Lugli, S.; Manzi, V.; Reghizzi, M.; Roveri, M.
abstract
The Terminal Carbonate Complex (TCC) is an upper Messinian shallow-water succession characterized by abundant oolites deposits and microbial-derived carbonates mainly known from the Western Mediterranean. The importance of the TCC derives from the close relation of its deposition with the Messinian salinity crisis and from the presence of large and diversified microbialite assemblages, which represent a rare occurrence in the Cenozoic marine sedimentary record. In this paper we provide the first detailed description of a carbonate system closely comparable to the TCC located in the central Mediterranean. This succession crops out at the southern end of the Salento Platform (South-eastern Italy) and has been investigated by means of stratigraphic, sedimentary, palaeontological and Sr isotopes analyses. Special attention has been given to the microbialite facies, with a detailed textural characterization focused on the reconstruction of their depositional and palaeoenvironmental settings. The Salento Platform TCC mainly consists of oolites deposits, Porites colonization and a diversified microbialite assemblage including six different facies, which developed mostly under shallow-water, normal marine salinity and warm climatic conditions. The overall stacking pattern is given by the superposition of three main sequences, each one including lowstand, transgressive and highstand system tracts. The Salento Platform TCC is dated to the late Messinian; our microfacies and geochemical data suggest that it could have developed during the first stage of the MSC; these carbonates are in fact followed by a sharp unconformity sealed by thick breccia deposits, possibly related to the onset of the Messinian erosional surface and to the subsequent stages of the Messinian salinity crisis.
2022
- Strontium isotope stratigraphic insights on the end-Permian mass extinction and the Permian-Triassic boundary in the Dolomites (Italy)
[Articolo su rivista]
Garbelli, C.; Cipriani, A.; Brand, U.; Lugli, F.; Posenato, R.
abstract
The Dolomites (Southern Alps, Italy) is a most significant region to investigate the evolution of shallow-marine ecosystems during the end-Permian mass extinction (EPME). Shallow-marine ecosystems are complex places from an oceanographic viewpoint and combine high biological productivity and ecological diversity. Therefore, establishing the timing and correlation of globally recognisable events in this region are fundamental to interpreting the biological crisis that followed. We took advantage of the Strontium Isotope Stratigraphy (SIS) concept to correlate our stratigraphic succession, ranging from the upper Bellerophon (Bulla Member, upper Changhsingian) to the lower Werfen (Tesero Member, upper Changhsingian - lower Induan) Formations of the Dolomites, to the Meishan (Zhejiang Province, China), the Global Stratotype Section and Point (GSSP) for the Permian–Triassic boundary. We integrated new and previously published 87Sr/86Sr data from well preserved brachiopods and show that the topmost part of the Bellerophon Formation (the Bulla Member) correlates with beds 24 e-f of the GSSP section, while the Tesero Member, where the Permian-Triassic boundary is located, is characterised by more radiogenic Sr isotope ratios than expected. Differences in Sr isotope ratios may be due to small-scale variations in local paleoenvironmental and paleogeographic conditions/settings. Continental weathering of sedimentary or igneous rocks, distance from terrestrial environment and nearby occurrence of radiogenic rocks might also produce locally variable Sr isotope signatures especially in shallow water environments complicating the application of SIS principles.
2022
- Strontium isotope stratigraphy of late Cenozoic fossiliferous marine deposits in North Borneo (Brunei, and Sarawak, Malaysia)
[Articolo su rivista]
Kocsis, László; Briguglio, Antonino; Cipriani, Anna; Frijia, Gianluca; Vennemann, Torsten; Baumgartner, Claudia; Roslim, Amajida
abstract
Neogene marine deposits of North Borneo are locally very rich in fossils that provide glimpses into the past biodiversity. However, dating these onshore sediments with biostratigraphy is often hampered by the lack and/or the poor preservation state of index fossils. Therefore, the fossiliferous sites were targeted with strontium isotope stratigraphy (SIS) to obtain higher precision relative dating. Well-preserved macrofossils were screened using a multidisciplinary approach, and 87Sr/86Sr ratios of the most pristine remains were used to date the embedding sediments. Most of the measured ages fall in the expected chronostratigraphic framework established by large scale studies for the region. The oldest, Burdigalian (early Miocene) ages were measured for the Sibuti Formation in Sarawak (17.71 ± 0.2My and 16.7 ± 0.2My) followed by a Serravallian (middle Miocene) age within the Belait Fm in Brunei (12.1 +1.4/-1.2My). Eight localities from the younger units, the Miri and Seria formations in Brunei, gave a range in age from 10.5 ± 1 to 7.0 +0.9/-0.5My (Tortonian-Messinian). Reworked fossil assemblages from Tutong beach were also investigated and the SIS ages of Late Miocene support an origin from the younger part of the Seria Fm. One locality, in Lumapas where limestone crops out in Brunei, gave an unexpected younger age (Tortonian, late Miocene, 10.6 ± 1My) compared to estimates projected for its assumed stratigraphic position in the lower Belait Formation (late Burdigalian). These challenging data require more research, yet if the young age is accepted, the stratigraphic situation of the limestone needs further revision.
2021
- Enriched Hf–Nd isotopic signature of veined pyroxenite-infiltrated peridotite as a possible source for E-MORB
[Articolo su rivista]
Borghini, G.; Rampone, E.; Class, C.; Goldstein, S.; Cai, Y.; Cipriani, A.; Hofmann, A. W.; Bolge, L.
abstract
Pyroxenite-peridotite sequences from the External Liguride (EL) Jurassic ophiolites (Northern Apennines, Italy) consist of portions of fertile MORB mantle that were modified by deep melt infiltration and melt-peridotite reaction. They represent an excellent natural example of a MORB-like veined mantle including unmodified peridotite, pyroxenite layers and metasomatized peridotite. We carried out a spatially controlled Hf isotope study on these mantle sequences to investigate how the Nd and Hf isotopic systems are affected by pyroxenite emplacement and melt-peridotite interactions. Present-day Lu–Hf isotopic compositions of these lithologies show a large range of 176Lu/177Hf and 176Hf/177Hf ratios that are correlated with their Nd isotopic compositions. Pyroxenite-free peridotites delineate a Hf–Nd isotope array that corresponds to a Proterozoic age (> 1.5 Ga) which is likely related to the accretion to the subcontinental lithosphere of this mantle sector. Heterogeneous 176Hf/177Hf isotopic compositions in pyroxenites mostly correlate with the significant variations of 176Lu/177Hf ratios and reflect variable garnet abundance in the primary modal assemblage. Over time, the pyroxenites acquired a large range of εHf values, which encompass the global range of Hf–Nd isotopes in ocean ridge basalts. Infiltration of pyroxenite-derived melts led the host peridotite to acquire low Lu/Hf ratios with the consequent development of 176Hf/177Hf ratios lower than in the unmodified peridotite, generating an equivalent of an enriched mantle component. This melt-peridotite interaction likely occurred during the pyroxenite emplacement 430 Ma ago, as confirmed by two Lu–Hf local pyroxenite-peridotite isochrons. The chemical and isotopic changes produced, over time, a spread of Hf–Nd isotopic signatures of the EL veined mantle, covering almost the entire range of published MORB compositions. Pyroxenite emplacement and local metasomatism of the host peridotites thus created Hf–Nd enriched mantle domains, making the EL veined mantle the first reported natural example of an enriched MORB-like mantle that formed through the combined effect of deep emplacement of pyroxenite and pyroxenite-peridotite interaction. The structure and isotopic characteristics of the EL veined mantle were used to model the isotopic compositions of melts produced by decompression melting of three-component heterogeneous mantle sources, providing an additional scenario to the generation of EMORB erupted at mid-ocean ridge settings. Our results emphasize the potential role of deep pyroxenite infiltration in modifying the host peridotites by interaction with pyroxenite-derived melts and creating heterogeneous mantle domains.
2021
- Forebulge migration in the foreland basin system of the central-southern Apennine fold-thrust belt (Italy): New high-resolution Sr-isotope dating constraints
[Articolo su rivista]
Sabbatino, M.; Tavani, S.; Vitale, S.; Ogata, K.; Corradetti, A.; Consorti, L.; Arienzo, I.; Cipriani, A.; Parente, M.
abstract
The Apennines are a retreating collisional belt where the foreland basin system, across large domains, is floored by a subaerial forebulge unconformity developed due to forebulge uplift and erosion. This unconformity is overlain by a diachronous sequence of three lithostratigraphic units made of (a) shallow-water carbonates, (b) hemipelagic marls and shales and (c) siliciclastic turbidites. Typically, the latter two have been interpreted regionally as the onset of syn-orogenic deposition in the foredeep depozone, whereas little attention has been given to the underlying unit. Accordingly, the rate of migration of the central-southern Apennine fold-thrust belt-foreland basin system has been constrained, so far, exclusively considering the age of the hemipelagites and turbidites, which largely post-date the onset of foredeep depozone. In this work, we provide new high-resolution ages obtained by strontium isotope stratigraphy applied to calcitic bivalve shells sampled at the base of the first syn-orogenic deposits overlying the Eocene-Cretaceous pre-orogenic substratum. Integration of our results with published data indicates progressive rejuvenation of the strata sealing the forebulge unconformity towards the outer portions of the fold-thrust belt. In particular, the age of the forebulge unconformity linearly scales with the pre-orogenic position of the analysed sites, pointing to an overall constant migration velocity of the forebulge wave in the last 25 Myr.
2021
- Insights on the origin of vitrified rocks from serravuda, acri (Italy): Rock fulgurite or anthropogenic activity?
[Articolo su rivista]
Elmi, C.; Cipriani, A.; Lugli, F.; Sighinolfi, G.
abstract
In this study, twenty five partially vitrified rocks and four samples of vitrified rocks collected on the top hill called Serravuda (Acri, Calabria, Italy) are analyzed. The goal is to shed light on the origin of these enigmatic vitrified materials. The analyzed vitrified rocks are a breccia of cemented rock fragments (gneiss, granitoid, and amphibolite fragments) which extends for more than 10 m, forming a continuous mass along the northern and north-west border of the flat top hill. Surrounded by the vitrified accumulation, exposed Paleozoic granitoid substrate rocks show limited melting or heat-alteration processes. By mapping minerals embedded in the glass matrix via X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM), an interpretation of source rock material, reactions, and thermometric indications to form vitrified materials on the top hill of Serravuda, Acri (Italy), is provided. The mineralogical composition of heated or partially vitrified samples is heterogeneous owing to the effects of heating events, but it mostly recalls the parent rock composition (gneiss, granitoid, and amphibolite). The presence of quartz, cristobalite, tridymite, mullite, plagioclase, hercynite, cordierite, and olivine in Serravuda partially vitrified rocks and glasses suggests that samples were subjected to pyrometamorphism and the temperature range at which the glass formed was about 1000–1100◦C in the presence of hydrous gas, burning organic material (e.g., wood), and assuming thermodynamic equilibrium. Lithologies of the heated or partially vitrified rock fragments are a mixture of parent rocks not outcropping on the top of the hill such as gneiss and amphibolite. Data suggest that Serravuda vitrified rocks are most likely the result of anthropic activities and could represent remnants of vitrified fort walls. The mineral assemblage of partially vitrified rocks and glasses suggests that the fort walls were made of slabs derived from the local metamorphic rocks with the addition of Serravuda substrate Paleozoic granitoid rocks to improve the strength and insulation of the fort walls.
2021
- Mechanical behavior of the shallow part of megathrusts: hints from the Sestola Vidiciatico tectonic Unit (Northern Apennines, Italy)
[Abstract in Atti di Convegno]
Remitti, F.; Mittempergher, S.; Festa, A.; Cipriani, A.; Lugli, F.
abstract
2021
- Postmelting hydrogen enrichment in the oceanic lithosphere
[Articolo su rivista]
Le Roux, Veronique; Urann, Benjamin M.; Brunelli, Daniele; Bonatti, Enrico; Cipriani, Anna; Demouchy, Sylvie; Monteleone, Brian D.
abstract
The large range of H2O contents recorded in minerals from exhumed mantle rocks has been challenging to interpret, as it often records a combination of melting, metasomatism, and diffusional processes in spatially isolated samples. Here, we determine the temporal variations of H2O contents in pyroxenes from a 24-Ma time series of abyssal peridotites exposed along the Vema fracture zone (Atlantic Ocean). The H2O contents of pyroxenes correlate with both crustal ages and pyroxene chemistry and increase toward younger and more refractory peridotites. These variations are inconsistent with residual values after melting and opposite to trends often observed in mantle xenoliths. Postmelting hydrogen enrichment occurred by ionic diffusion during cryptic metasomatism of peridotite residues by low-degree, volatile-rich melts and was particularly effective in the most depleted peridotites. The presence of hydrous melts under ridges leads to widespread hydrogen incorporation in the oceanic lithosphere, likely lowering mantle viscosity compared to dry models.
2021
- Testing miniaturized extraction chromatography protocols for combined 87Sr/86Sr and δ88/86Sr analyses of pore water by MC-ICP-MS
[Articolo su rivista]
Argentino, C.; Lugli, F.; Cipriani, A.; Panieri, G.
abstract
We tested two miniaturized extraction chromatography protocols for strontium isolation based on 300 μL (Protocol 1) and 30 μL (Protocol 2) column volumes of Sr-Spec resin, for the simultaneous determination of 87Sr/86Sr and δ88/86Sr by MC-ICP-MS. The accuracy and precision of the Sr isotope ratios have been evaluated by analyzing JCt-1 and SRM 1640a reference materials, resulting in a reproducibility of 87Sr/86Sr and δ88/86Sr values of 0.000026 and 0.04‰ (Protocol 1) (2SD, n = 3), and of 0.000074 and 0.13‰ (Protocol 2) (2SD, n = 4), respectively. The Sr isotopic composition of SRM 1640a, presented here for the first time, is 87Sr/86Sr = 0.708790 ± 0.000062 and δ88/86Sr = 0.07 ± 0.10‰ (2SD, n = 6). Protocols 1 and 2 were successfully applied to pore waters extracted from marine sediment cores from the northern Barents Sea. Our results demonstrate that both protocols attain accurate 87Sr/86Sr ratios and allow the detection of natural variations in δ88/86Sr in marine pore waters. Compared to previous Sr/matrix separation methods, Protocol 2 is significantly less costly, making it particularly suitable for large-scale oceanological and limnological studies.
2020
- A focus on the Middle to Upper Palaeolithic transition in the Mediterranean area
[Articolo su rivista]
Benazzi, S.; Arrighi, S.; Badino, F.; Bortolini, E.; Figus, C.; Lugli, F.; Marciani, G.; Oxilia, G.; Romandini, M.; Silvestrini, S.; Boscato, P.; Cipriani, A.; Moroni, A.; Negrino, F.; Peresani, M.; Pini, R.; Ravazzi, C.; Ronchitelli, A.; Spinapolice, E.
abstract
2020
- Backdating systematic shell ornament making in Europe to 45,000 years ago
[Articolo su rivista]
Arrighi, S.; Bortolini, E.; Tassoni, L.; Benocci, A.; Manganelli, G.; Spagnolo, V.; Foresi, L. M.; Bambini, A. M.; Lugli, F.; Badino, F.; Aureli, D.; Boschin, F.; Figus, C.; Marciani, G.; Oxilia, G.; Silvestrini, S.; Cipriani, A.; Romandini, M.; Peresani, M.; Ronchitelli, A.; Moroni, A.; Benazzi, S.
abstract
Personal ornaments are commonly linked to the emergence of symbolic behavior. Although their presence in Africa dates back to the Middle Stone Age, evidence of ornament manufacturing in Eurasia are sporadically observed in Middle Palaeolithic contexts, and until now, large-scale diffusion has been well documented only since the Upper Palaeolithic. Nevertheless, little is known during the period between ca. 50,000 and 40,000 years ago (ka), when modern humans colonized Eurasia replacing existing hominin populations such as the Neandertals, and a variety of “transitional” and/or early Upper Palaeolithic cultures emerged. Here, we present shell ornaments from the Uluzzian site of Grotta del Cavallo in Italy, southern Europe. Our results show evidence of a local production of shell beads for ornamental purposes as well as a trend toward higher homogeneity in tusk bead shape and size over time. The temporal interval of the layers of interest (45–40 ka) makes Cavallo the earliest known shell ornament making context in Europe.
2020
- Constraining the onset of flexural subsidence and peripheral bulge extension in the Miocene foreland of the southern Apennines (Italy) by Sr-isotope stratigraphy
[Articolo su rivista]
Sabbatino, M.; Vitale, S.; Tavani, S.; Consorti, L.; Corradetti, A.; Cipriani, A.; Arienzo, I.; Parente, M.
abstract
In fold and thrust belts developing at convergent margins, the migration of the advancing wedge is accompanied by bulging of the downgoing plate, followed by the development of a foredeep basin filled by a thick succession of syn-orogenic sediments. The transition from forebulge to foredeep marks a key moment in the evolution of the orogenic system. In deep water environments, the record of this transition is typically complete and progressive. Conversely, in the shallow-water/continental environment of many collisional systems, the uplift of the forebulge area can imply emersion and erosion, obliterating the stratigraphic record of key steps of the evolution of the orogenic system. The southern Apennines constitute one of these collisional fold and thrust belts where the development of the forebulge has implied emersion and erosion, with the development of a Miocene forebulge erosional unconformity, accompanied by extensional deformation associated with the bending of the lithosphere during the forebulge stage. In this paper, we use strontium isotope stratigraphy to constrain with unprecedented time-resolution the age of the forebulge unconformity in areas presently incorporated in the northern sector of the southern Apennines fold and thrust belt. Integration of our results and those of previous studies indicates, at the regional scale, a younging toward the foreland of the forebulge unconformity across the belt. Our high-resolution ages also reveal a diachronous onset of the flexural subsidence over short distances, associated with the occurrence of horst and graben structures, possibly resulting from inherited paleotopography along with forebulge extension. This work highlights how high-resolution dating is critical to unravel the evolution of foreland basin systems at different scales.
2020
- Cyclical variations of fluid sources and stress state in a shallow megathrust zone mélange
[Articolo su rivista]
Cerchiari, Anna; Remitti, Francesca; Mittempergher, Silvia; Festa, Andrea; Lugli, Federico; Cipriani, Anna
abstract
Differences in REE patterns of calcite from extensional and shear veins of the Sestola Vidiciatico Tectonic Unit in Northern Apennines suggest variations in fluid source during the seismic cycle in an ancient analogue of a shallow megathrust (Tmax ̴100°-150°C). In shear veins, a positive Eu anomaly suggests an exotic fluid source, likely hotter than the fault environment. Small-scale extensional veins were derived instead from a local fluid in equilibrium with the fault zone rocks. Mutually crosscutting relations between two sets of extensional veins, parallel and perpendicular to the megathrust, suggest a repeated shifting of the σ1 and σ3 stresses during the seismic cycle. This is consistent with: (i) a seismic phase, with brittle failure along the thrust, crystallization of shear veins from an exotic fluid, stress drop and stress rotation; (ii) a post-seismic phase, with fault-normal compaction and formation of fault-normal extensional veins fed by local fluids; (iii) a reloading phase, where shear stress and pore pressure are gradually restored and fault-parallel extensional veins form, until the thrust fails again. The combination of geochemical and structural analyses in veins from exhumed megathrust analogues represents a promising tool to better understand the interplay between stress state and fluids in modern subduction zones.
2020
- Early life of Neanderthals
[Articolo su rivista]
Nava, A.; Lugli, F.; Romandini, M.; Badino, F.; Evans, D.; Helbling, A. H.; Oxilia, G.; Arrighi, S.; Bortolini, E.; Delpiano, D.; Duches, R.; Figus, C.; Livraghi, A.; Marciani, G.; Silvestrini, S.; Cipriani, A.; Giovanardi, T.; Pini, R.; Tuniz, C.; Bernardini, F.; Dori, I.; Coppa, A.; Cristiani, E.; Dean, C.; Bondioli, L.; Peresani, M.; Muller, W.; Benazzi, S.
abstract
The early onset of weaning in modern humans has been linked to the high nutritional demand of brain development that is intimately connected with infant physiology and growth rate. In Neanderthals, ontogenetic patterns in early life are still debated, with some studies suggesting an accelerated development and others indicating only subtle differences vs. modern humans. Here we report the onset of weaning and rates of enamel growth using an unprecedented sample set of three late (∼70 to 50 ka) Neanderthals and one Upper Paleolithic modern human from northeastern Italy via spatially resolved chemical/isotopic analyses and histomorphometry of deciduous teeth. Our results reveal that the modern human nursing strategy, with onset of weaning at 5 to 6 mo, was present among these Neanderthals. This evidence, combined with dental development akin to modern humans, highlights their similar metabolic constraints during early life and excludes late weaning as a factor contributing to Neanderthals’ demise.
2020
- Fast offline data reduction of laser ablation MC-ICP-MS Sr isotope measurements: Via an interactive Excel-based spreadsheet 'SrDR'
[Articolo su rivista]
Lugli, F.; Weber, M.; Giovanardi, T.; Arrighi, S.; Bortolini, E.; Figus, C.; Marciani, G.; Oxilia, G.; Romandini, M.; Silvestrini, S.; Jochum, K. P.; Benazzi, S.; Cipriani, A.
abstract
Strontium isotopes are applied to a wide range of scientific fields and to different types of materials, providing valuable information foremost about provenance and age, but also on diagenetic processes and mixing relationships between different Sr reservoirs. The development of in situ analytical techniques, such as laser ablation ICP-MS, has improved our understanding of Sr isotope variability in several fields of application, because of the possibility to discriminate small-scale changes and their spatial distribution. However, large outputs of Sr isotope data are produced by laser ablation MC-ICP-MS systems, which necessitate multiple offline steps to correct and assess the data. This requires the availability of simple and user-friendly tools, easily manageable by non-specialists too. With this in mind, we developed SrDR, an Excel-based interactive data reduction spreadsheet ('SrDR', Sr-Data-Reduction) for the processing of Sr isotopes measured by LA-MC-ICP-MS. The SrDR spreadsheet is easily customizable (a) to meet user-specific analytical protocols, (b) for different instruments (i.e. Nu plasma vs. Neptune), and (c) for diverse target materials (e.g. rare earth element enriched or depleted samples). We also include several examples relevant to low and high temperature geochemistry fields-a fossil tooth, a modern seashell, a speleothem sample and plagioclase crystals-to show how different sample materials are corrected for different interfering masses.
2020
- Geochemistry of recent and fossil brachiopod calcite of Megathiris detruncata (Terebratulida, Megathyrididae): A modern baseline study to trace past environmental conditions
[Articolo su rivista]
Kocsis, L.; Dulai, A.; Cipriani, A.; Vennemann, T.; Yunsi, M.
abstract
Modern and fossil calcareous shells of the terebratulide brachiopod Megathiris detruncata have been investigated for stable oxygen and carbon isotope and elemental (Mg, Sr, Mn, Fe, Ba) compositions to assess the possibility of using this species to trace past environmental conditions. Modern shells were collected from the Mediterranean Sea and the Atlantic Ocean, while fossil specimens were sampled from late Eocene to Pleistocene deposits in Europe. We mainly analysed bulk shells (i.e., primary and secondary layers together) but, in some cases, their single median and lateral septa, ventral and dorsal valves. The oxygen and carbon isotope compositions of the modern shells indicate that M. detruncata mineralizes the bulk of its calcite shell in equilibrium with seawater. In addition, their Mn, Ba, and Fe concentrations are low with few exceptions from the Atlantic Ocean where high Fe/Ca ratios can probably be related to locally enhanced Fe availability. The Sr/Ca ratio ranges narrowly between 1.4 and 1.7 mmol/mol, while the Mg/Ca ratio has larger variability from about 23 to 45 mmol/mol. The δ18O derived temperatures do not correlate with Mg/Ca, suggesting that Mg is likely affected by greater vital effects. Physiological control on biomineralization might also explain the somewhat larger spread of δ13C between different valves of the same individual and will require further testing by in situ analyses. The fossil M. detruncata shells have a compositional range much larger than modern specimens, with large intra-shell and intra-site variabilities indicative of partial or full alteration. Altered fossils, characterized by low δ18O and δ13C values, low Mg/Ca and Sr/Ca, and high Mn/Ca and Fe/Ca ratios are often associated with clear signs of re-crystallization and/or secondary calcite precipitation within the shells. We used fossil samples without obvious recrystallization features and chemical and isotopic compositions similar to modern specimens to discuss environmental parameters such as temperature and δ18Oseawater at the given time. We recognized variable local controls on seawater isotopic compositions in the Paratethys from the Oligocene until the Middle Miocene, and we propose somewhat warmer habitats for the M. detruncata in the Aquitaine Basin in southwestern France during the Late Oligocene. Isotope variation recorded in the Plio-Pleistocene Mediterranean shells are instead best explained by changing glacial-interglacial conditions.
2020
- High H2O Content in Pyroxenes of Residual Mantle Peridotites at a Mid Atlantic Ridge Segment
[Articolo su rivista]
Li, Pei; Xia, Qun-Ke; Dallai, Luigi; Bonatti, Enrico; Brunelli, Daniele; Cipriani, Anna; Ligi, Marco
abstract
Global correlations of mid-ocean-ridges basalt chemistry, axial depth and crustal thickness have been ascribed to mantle temperature variations affecting degree of melting. However, mantle H2O content and elemental composition may also play a role. How H2O is distributed in the oceanic upper mantle remains poorly constrained. We tackled this problem by determining the H2O content of orthopyroxenes (opx) and clinopyroxenes (cpx) of peridotites from a continuous lithospheric section created during 26 Ma at a 11°N Mid-Atlantic Ridge segment, and exposed along the Vema Transform. The H2O content of opx ranges from 119 ppm to 383 ppm; that of cpx from 407 ppm to 1072 ppm. We found anomalous H2O-enriched peridotites with their H2O content not correlating inversely with their degree of melting, although H2O is assumed to be incompatible during melting. Inverse correlation of H2O with Ce, another highly incompatible component, suggests post-melting H2O enrichment. We attribute a major role to post-melting temperature-dependent diffusion of hydrogen occurring above the melting region, where water-rich melt flows faster than residual peridotites through dunitic conduits cross-cutting the uprising mantle. Accordingly, estimates of the H2O content of the MORB mantle source based on H2O in abyssal peridotites can be affected by strong uncertainties.
2020
- Mantle heterogeneities produced by open-system melting and melt/rock reactions in Patagonian extra-Andean backarc mantle (Paso de Indios, Argentina)
[Articolo su rivista]
Bertotto, Gustavo W.; Mazzucchelli, Maurizio; Zanetti, Alberto; Ponce, Alexis D.; Giovanardi, Tommaso; Brunelli, Daniele; Bernardi, Mauro I.; Hémond, Christophe; Cipriani, Anna
abstract
The Eocene basaltic extrusions in the Paso de Indios region (Chubut-Argentina) are one manifestation of the extensional tectonism of the active margin of South America during the Cenozoic. Ultramafic xenoliths embedded in these volcanics are mainly harzburgites and lherzolites with subordinate pyroxenites, estimated equilibrium temperatures ranging from 853 ± 15 to 1057 ± 32°C and pressures in the spinel stability field.
Geochemical and modal evidences point to a multistage magmatic history with record of a last reactional open-system episode associated to the influx of adakitic-like melts in a orthopyroxene-rich, clinopyroxene-poor mantle column. The great variability of clinopyroxene modal and geochemical composition in a ∼20 km2 area suggests extreme variability of the physical parameters connected to melt infiltration and melt/rock reactions processes at a very small scale superimposed on a mantle with an inherited meter scale heterogeneity. Variations in the melt influx rate and residual porosity of the mantle column produced different melt/rock reactions which could be summarized in two entangled main reaction pathways: 1) opx+cpx+melt1-->ol+melt2 and 2) opx+melt1-->cpx+ol+melt2. These reactions deeply modified the trace elements content of clinopyroxenes producing variable enrichments in LREEs and LILEs related to both chromatographic and pure incremental open system processes.
Petrological evidence suggests that the last reactional process occurred in the spinel stability field overprinting a strongly depleted mantle that, in a previous stage, had experienced extreme depletion in the garnet stability field, possibly under hydrous conditions.
The adakitic-like nature of the influxing melt associates this episode to the subduction system along the western margin of South America, active at least since Triassic times.
2020
- Origin of oceanic ferrodiorites by injection of nelsonitic melts in gabbros at the Vema Lithospheric Section, Mid Atlantic Ridge
[Articolo su rivista]
Brunelli, Daniele; Sanfilippo, Alessio; Bonatti, Enrico; Skolotnev, Sergei; Escartin, Javier; Ligi, Marco; Ballabio, Giorgia; Cipriani, Anna
abstract
Oxide gabbros are a minor but diffuse component of the lower oceanic crust. Their presence poses questions on
lower crust exhumation processes and magma differentiation at mid ocean ridges because they are systematically
associated with shear zones and are hardly explained by classical fractionation and meltmigration models.
Here, we report on a study of lower-crust gabbros recovered from the Vema Lithospheric Section at 11°N along
theMid Atlantic Ridge, where oxide gabbros are abnormally abundant relative to ridge centred magmatic intrusives
and where we found a peculiar lithological occurrence represented by deformed diorites extremely
enriched in Fe-Ti-oxides and apatites. Their complex genetic history reveals a hybrid nature consistent with derivation
from high pressure injections of Fe-Ti-P saturated nelsonitic melts in a primitive gabbroic groundmass
that induced fracturing, de-compaction, mineral resorption and chemical re-equilibration. Melt injections may
occur after intense ductile shearing at the edges of the axial magma chamber following lateral differentiation
of primitivemelts injected at the centre of the ridge axis segment.We propose a regime of lateral, instead of vertical,
melt differentiation along the ridge axis and a possible role formelt immiscibility in the formation of Fe-Ti-P
melt pockets in oceanic domains.
2020
- Peopling dynamics in the Mediterranean area between 45 and 39 ky ago: State of art and new data
[Articolo su rivista]
Benazzi, Stefano; Arrighi, Simona; Badino, Federica; Bortolini, Eugenio; Figus, Carla; Lugli, Federico; Marciani, Giulia; Oxilia, Gregorio; Romandini, Matteo; Silvestrini, Sara; Boscato, Paolo; Cipriani, Anna; Moroni, Adriana; Negrino, Fabio; Peresani, Marco; Pini, Roberta; Ravazzi, Cesare; Ronchitelli, Annamaria; Spinapolice, Enza
abstract
2020
- Terrestrial target and melting site of Libyan Desert Glass: New evidence from trace elements and Sr isotopes
[Articolo su rivista]
Sighinolfi, G. P.; Lugli, F.; Piccione, F.; Michele, V. D. E.; Cipriani, A.
abstract
Strontium isotopes and selected trace elements (Rb, Sr, REE, Zr, Hf, Th, and U) were measured on samples of Libyan Desert Glass (LDG) and a series of terrestrial materials (rocks, LDG-bearing soils, eolic sand) collected over a large area of southwestern Egypt to identify the LDG terrestrial parent material and the site where impact melting occurred. Samples include Upper Cretaceous hypersilicic sandstones outcropping at or near the LDG strewn field and Lower Cretaceous to Silurian sandstones from the Gilf Kebir Plateau highlands. Strontium isotopes and partially Zr, Hf, Th, and U, possibly reflecting the composition of detrital zircon grains, are effective indicators of the geochemical affinity between terrestrial materials and LDG, unlike Rb, Sr, and REE abundances. The best geochemical affinity with LDG was found in LDG-bearing soils collected at the base of intradunal corridors in the Great Sand Sea. Remarkably, abundances of the Zr group elements of the LDG Zr-bearing phase are distinct from all terrestrial detrital zircons from the area. We suggest a mixture of weathering products from sandstones of different ages, including Devonian and Silurian rocks from the Gilf Kebir highlands, as the most likely source for LDG. A loose sedimentary formation exposed 29 Ma ago at the Earth’s surface, superimposed over hard bedrock, might have been the true terrestrial target of the impact, but because of its incoherent nature, it was rapidly destroyed, explaining the complete absence of any evidence of an impact structure.
2019
- A deep fluid source of radiogenic Sr and highly dynamic seepage conditions recorded in Miocene seep carbonates of the northern Apennines (Italy)
[Articolo su rivista]
Argentino, C.; Lugli, F.; Cipriani, A.; Conti, S.; Fontana, D.
abstract
The 87Sr/86Sr, REE and MoU systematics were investigated in Miocene seep carbonates formed on accretionary ridges at the front of the northern Apennine wedge. Here we evaluate fluid sources, seepage intensity and redox conditions during carbonate precipitation. Micrite matrix and early calcite cements lining cavities are the main authigenic carbonate phases and show negligible diagenetic alteration. Their AOM-related (anaerobic oxidation of methane) origin is evident from δ13C values ranging from −38.7‰ to −25.7‰. The 87Sr/86Sr ratios in carbonates vary between 0.708659 and 0.709132. Most micrite values fall within the range of Middle Miocene seawater (Langhian, MNN5a biozone), in agreement with the biostratigraphy of the host sediments, thus reflecting precipitation of seep carbonates close to the seafloor. Highly radiogenic 87Sr/86Sr ratios, of early calcite cements and micrite from conduit-rich facies at the base of carbonate bodies, likely derived from the interaction of fluids with detrital clays during the fault-controlled upward migration through the underlying terrigenous turbidite successions. Strong Mo and U enrichments in carbonates, with MoEF and UEF up to 233.5 and 86.6 respectively, coupled with (Mo/U)EF ratios ranging between 0.7 and 9.7, indicate dynamic redox conditions, episodically sulfidic and restricted to porewaters. This interpretation is also supported by enrichments in MREE of micrites and a general absence of negative Ce anomalies. These new data provide an indirect indication of rates and temporal variability of AOM at fossil methane seeps developed on a thrust related anticline and help to constrain the complex interaction between fluid migration pathways, seepage intensity and environmental conditions as observed in modern seep analogues.
2019
- Enamel peptides reveal the sex of the Late Antique ‘Lovers of Modena’
[Articolo su rivista]
Lugli, F.; Di Rocco, G.; Vazzana, A.; Genovese, F.; Pinetti, D.; Cilli, E.; Carile, M. C.; Silvestrini, S.; Gabanini, G.; Arrighi, S.; Buti, L.; Bortolini, E.; Cipriani, A.; Figus, C.; Marciani, G.; Oxilia, G.; Romandini, M.; Sorrentino, R.; Sola, M.; Benazzi, S.
abstract
Recent work has disclosed the critical role played by enamel peptides in sex classification of old skeletal remains. In particular, protein AMELY (amelogenin isoform Y) is present in the enamel dental tissue of male individuals only, while AMELX (isoform X) can be found in both sexes. AMELY can be easily detected by LC-MS/MS in the ion extracted chromatograms of the SM(ox)IRPPY peptide (monoisotopic [M + 2 H]+2 mass = 440.2233 m/z). In this paper, we exploited the dimorphic features of the amelogenin protein to determine the sex of the so-called ‘Lovers of Modena’, two Late Antique individuals whose skeletons were intentionally buried hand-in-hand. Upon discovery, mass media had immediately assumed they were a male-female couple, even if bad preservation of the bones did not allow an effective sex classification. We were able to extract proteins from the dental enamel of both individuals (~1600 years old) and to confidently classify them as males. Results were compared to 14 modern and archaeological control samples, confirming the reliability of the ion chromatogram method for sex determination. Although we currently have no information on the actual relationship between the ‘Lovers of Modena’ (affective? Kin-based?), the discovery of two adult males intentionally buried hand-in-hand may have profound implications for our understanding of funerary practices in Late Antique Italy.
2019
- Strontium and stable isotope evidence of human mobility strategies across the Last Glacial Maximum in southern Italy
[Articolo su rivista]
Lugli, Federico; Cipriani, Anna; Capecchi, Giulia; Ricci, Stefano; Boschin, Francesco; Boscato, Paolo; Iacumin, Paola; Badino, Federica; Mannino, Marcello A.; Talamo, Sahra; Richards, Michael P.; Benazzi, Stefano; Ronchitelli, Annamaria
abstract
Understanding the reason(s) behind changes in human mobility strategies through space and time is a major challenge in palaeoanthropology. Most of the time this is due to the lack of suitable temporal sequences of human skeletal specimens during critical climatic or cultural shifts. Here, we present temporal variations in the Sr isotope composition of 14 human deciduous teeth and the N and C stable isotope ratios of four human remains from the Grotta Paglicci site (Apulia, southern Italy). The specimens were recovered from the Gravettian and Epigravettian layers, across the Last Glacial Maximum, and dated between 31210–33103 and 18334–19860 yr cal bp (2σ). The two groups of individuals exhibit different 87Sr/86Sr ratios and, while the Gravettians are similar to the local macro-fauna in terms of Sr isotopic signal, the Epigravettians are shifted towards higher radiogenic Sr ratios. These data, together with stable isotopes, can be explained by the adoption of different mobility strategies between the two groups, with the Gravettians exploiting logistical mobility strategies and the Epigravettians applying residential mobility.
2018
- Birth of an ocean in the Red Sea: Oceanic-type basaltic melt intrusions precede continental rupture
[Articolo su rivista]
Ligi, Marco; Bonatti, Enrico; Bosworth, William; Cai, Yue; Cipriani, Anna; Palmiotto, Camilla; Ronca, Sara; Seyler, Monique
abstract
The role of magmatism in continental rupture at the birth of a new ocean is poorly understood. Continental rupture can take place with voluminous volcanism, as in the southern Red Sea, or in a relatively non-volcanic mode, as in the northern Red Sea. We report geophysical, geochemical and geochronological evidence suggesting that continental rupture in the northern Red Sea is preceded by MORB-type basaltic melt intrusions that cooled at depth forming gabbros at progressively shallower crustal levels as rifting progressed towards continental separation. One of these gabbros yielded an40Ar/39Ar age of 25 ± 6 Ma, suggesting intrusion during early rifting. A magma chamber we detected 3.5 km below Thetis Deep, an axial segment of initial oceanic crust accretion, represents the final stage in this progression. Oceanic crust accretion in the Red Sea rift starts first at depth before continental rupture and initiation of sea floor spreading.
2018
- Calcium Carbonate and Phosphate Reference Materials for Monitoring Bulk and Microanalytical Determination of Sr Isotopes
[Articolo su rivista]
Weber, Michael; Lugli, Federico; Jochum, Klaus Peter; Cipriani, Anna; Scholz, Denis
abstract
In situ laser ablation analyses rely on the microanalytical homogeneity of reference materials (RMs) and a similar matrix and mass fraction between unknown samples and RMs to obtain reliable results. Suitable carbonate and phosphate RMs for determination of Sr isotope ratios in such materials are limited. Thus, we determined 87Sr/86Sr ratios of several carbonate (JCt-1, JCp-1, MACS-1, MACS-3) and phosphate (MAPS-4, MAPS-5, NIST SRM 1400, NIST SRM 1486) international RMs using dissolved samples and two different multi-collector inductively coupled plasma-mass spectrometers (MC-ICP-MS). Our Sr isotope data are in agreement with published data and have an improved measurement precision for some RMs. For MACS-1, we present the first 87Sr/86Sr value. We tested the suitability of these materials for microanalytical analyses by LA-MC-ICP-MS, with two different laser ablation systems: a conventional nanosecond laser and a state-of-the-art femtosecond laser. We investigated the RMs micro-homogeneity and compared the data with our solution data. Both laser ablation systems yielded identical 87Sr/86Sr ratios within uncertainty to the solution data for RMs with low interferences of REEs. Therefore, these carbonate and phosphate RMs can be used to achieve accurate and precise results for in situ Sr isotope investigations by LA-MC-ICP-MS of similar materials.
2018
- Comment on: metals in bones of the middle-aged inhabitants of Sardinia island (Italy) to assess nutrition and environmental exposure [Bocca et al. (2018), Environ Sci Pollut Res]
[Articolo su rivista]
Lugli, Federico; Cipriani, Anna
abstract
This comment addresses several inferences made by Bocca et al. (2018) to assess the nutrition of middle-aged inhabitants from four Sardinian localities (Alghero, Bisarcio, Geridu, and Sassari). Bocca et al. analyzed 72 human bone specimens dating from the twelfth to the eighteenth century for metal contents (Ba, Ca, Cd, Cu, Hg, Pb, Sr, and Zn) by SC-ICP-MS and applied a univariate and multivariate approach, using element-Ca ratios, to examine the eating habits and environmental exposure of the individuals. While we agree with their interpretation of the Hg/Ca and Pb/Ca ratios, attributable to various forms of environmental exposure, we disagree with some of their paleodiet claims.
2018
- Constraining the fluid source of Miocene seep carbonates using radiogenic Sr isotopes (Corella outcrop, northern Apennines, Italy)
[Abstract in Atti di Convegno]
Argentino, Claudio; Lugli, Federico; Cipriani, Anna; Conti, Stefano; Fioroni, Chiara; Fontana, Daniela
abstract
Analisi isotopiche e biostratigrafiche su corpi carbonatici metanoderivati dell'Appennino settentrionale
2018
- Highly dinamic redox condition and fluid source identification in seep impacted sediments revealed by Mo-U enrichments, 87Sr/86SR and REE pattern (Miocene, Mugello outcrops, northern Apennines)
[Abstract in Atti di Convegno]
Argentino, C.; Lugli, F.; Cipriani, A.; Conti, S.; Fioroni, C.; Fontana, D.
abstract
cold seeps have been increasingly identified.....
2018
- Isotopic constraints on contamination processes in the Tonian Goiás Stratiform Complex
[Articolo su rivista]
Giovanardi, Tommaso; Mazzucchelli, Maurizio; Lugli, Federico; Girardi, Vicente A. V.; Correia, Ciro T.; Tassinari, Colombo C. G.; Cipriani, Anna
abstract
The Tonian Goiás Stratiform Complex (TGSC, Goiás, central Brazil), is one of the largest mafic-ultramafic layered complexes in the world, emplaced during the geotectonic events that led to the Gondwana accretion. In this study, we present trace elements and in-situ U/Pb-Lu-Hf analyses of zircons and 87Sr/86Sr ratios of plagioclases from anorthosites and gabbros of the TGSC. Although formed by three isolated bodies (Cana Brava,Niquelândia and Barro Alto), and characterized by a Lower and Upper Sequence (LS and US), our new U/Pb zircon data confirm recent geochemical, geochronological, and structural evidences that the TGSC has originated from a single intrusive body in the Neoproterozoic. New Hf and Sr isotope ratios construe a complex contamination history for the TGSC,with different geochemical signatures in the two sequences. The low Hf and high Sr isotope ratios of the Lower Sequence (εHf(t) from−4.2 down to −27.5; 87Sr/86Sr=0.706605–0.729226), suggest the presence of a crustal component and are consistent with contamination from meta-pelitic and calc-silicate rocks found as xenoliths within the Seuence. The more radiogenic Hf isotope ratios and low Sr isotope composition of the Upper Sequence (εHf(t) from 11.3 down to −8.4; 87Sr/86Sr=0.702368–0.702452), suggest a contamination from mantle-derived metabasalts in agreement with the occurrences of amphibolite xenoliths in the US stratigraphy. The differential contamination of the two sequences is explained by the intrusion of the TGSC in a stratified crust dominated bymetasedimentary rocks in its deeper part andmetavolcanics at shallower levels. Moreover, the differential thermal gradient in the two crystallizing sequences might have contributed to the preservation and recrystallization of inherited zircon grains in the US and total dissolution or magmatic overgrowth of the LS zircons via melt/rock reaction processes.
2018
- Middle Pleistocene human and animal mobility at Isernia la Pineta: A strontium and oxygen isotope perspective
[Articolo su rivista]
Lugli, F; Cipriani, Anna; Julie, Arnaud; Marta, Arzarello; Giuseppe, Lembo; Renée, Janssen; Hubert, Vonhof; Carlo, Peretto; Stefano, Benazzi
abstract
In this work, we explored the isotopic composition of faunal (rodents, rhinoceros and bison) and human skeletal remains from the Middle Pleistocene layers of Isernia la Pineta (Molise, Italy). We particularly focused on high spatial resolution isotope analyses of tooth enamel by laser ablation MC-ICP-MS for strontium isotopes and by micro-drilling sampling for oxygen isotopes. Results from bone specimens were compared with the isotope variability of modern plants collected in the area surrounding the site, in a radius of about 30 km. While the human group seems local, macro-mammals show a higher degree of mobility.
2018
- Thermal effects of pyroxenites on mantle melting below mid-ocean ridges
[Articolo su rivista]
Brunelli, Daniele; Cipriani, Anna; Bonatti, Enrico
abstract
After travelling in Earth’s interior for up to billions of years, recycled material once injected at subduction zones can reach a subridge melting region as pyroxenite dispersed in the host peridotitic mantle. Here we study genetically related crustal basalts and mantle peridotites sampled along an uplifted lithospheric section created at a segment of the Mid-Atlantic Ridge through a time interval of 26 million years. The arrival of low-solidus material into the melting region forces the elemental and isotopic imprint of the residual peridotites and of the basalts to diverge with time. We show that a pyroxenite-bearing source entering the subridge melting region induces undercooling of the host peridotitic mantle, due to subtraction of latent heat by melting of the low-T-solidus pyroxenite. Mantle undercooling, in turn, lowers the thermal boundary layer, leading to a deeper cessation of melting. A consequence is to decrease the total amount of extracted melt, and hence the magmatic crustal thickness. The degree of melting undergone by a homogeneous peridotitic mantle is higher than the degree of melting of the same peridotite but veined by pyroxenites. This effect, thermodynamically predicted for a marble-cake-type peridotite–pyroxenite mixed source, implies incomplete homogenization of recycled material in the convective mantle.
2018
- Timing of the Rupelian transgression into the Upper Rhine Graben and Mainz Basin: a strontium stratigraphic approach on micro- and macrofossils
[Abstract in Atti di Convegno]
Tütken, T; Rosner, M; Lugli, F; Tütken, I; Grimm, K; Böhm, K; Weber, M; Walliser, E; Mertz, R; Jochum, Kp; Cipriani, A; Pirkenseer, C
abstract
The exact timing of the second Rupelian transgressions (sensu Hardenbol et al., 1998) into the Upper Rhine Graben (URG) and whether it was synchronous in the Mainz Basin (MzB) is not very precisely constrained. Biostratigraphic evidence place the beginning of the Rupel 2 transgression in the MzB into the Wallau Subformation (NP22-23) and at about the same time for the URG. Here we present the first comprehensive Sr isotope study on marine calcareous macro- and microfossils as well as a few shark teeth from various drill cores and outcrops of both settings, that ideally represent strata deposited at the base and top of the Rupel 2 transgression. Ostracods and foraminifers as well as some bivalve shells (oysters, Glycymeris sp.) and shark teeth were analysed for their Sr isotope composition. Microfossil preservation was assessed using single shell LA-ICP-MS-analysis to select only well-preserved specimens for high-precision TIMS or solution mode MC-ICP-MS Sr isotope analysis. Bivalves were screened by cathodoluminescence and LA-ICP-MS analysis for least altered areas in which intra-shell in situ LA-MC-ICP-MS Sr isotope analysis were made. The 87Sr/86Sr were compared to the global seawater Sr isotope curve of MacArthur et al. (2001) to infer the age and duration of the transgression. While 87Sr/86Sr of shark teeth and most oysters from Beuchille (except a few domains) were diagenetically altered, most ostracods and foraminifers from the URG are well-preserved, yielding a mean 87Sr/86Sr of 0.707960±0.000016 (n = 25; range: 0.707916 to 0.707985). These values enable us to infer a Sr stratigraphic age of 30.6±0.4 Ma for the late Rupelian regression and deposition of the „Cyrenenmergel“ in the URG and equivalent deposits in the Delémont Basin. Well-preserved foraminifers from the Bodenheim Formation in the MzB gave a mean 87Sr/86Sr of 0.707981±0.000012 (n = 8; range: 0.707964 to 0.707995). This yields a significantly (p<0.00002) younger Sr stratigraphic age of 30.1±0.3 Ma than for the URG deposits. Two aragonitic Glycymeris shells from the lower Alzey Formation (87Sr/86Sr = 0.707999) and Stadecken Formation (Albig Bank; 87Sr/86Sr = 0.707964) yield ages of 29.6 and 29.4 Ma, respectively. Thus the marine late Rupelian strata in the URG and MzB were probably deposited in about a million years.
2018
- Transhumance pastoralism of Roccapelago (Modena, Italy) early-modern individuals: Inferences from Sr isotopes of hair strands
[Articolo su rivista]
Lugli, Federico; Cipriani, Anna; Tavaglione, Valentina; Traversari, Mirko; Benazzi, Stefano
abstract
Objectives: In this work, we use Sr isotopes to analyze human hair and determine short-term movements of a contemporary human traveler and of early-modern individuals from an archaeological site (Roccapelago, Modena, Italy, 16th–18th century). Materials and methods: Analyses were performed using a Neptune MC–ICP–MS. We first set up and tested the procedure on scalp hair of a contemporary human, who spent some time between Brazil and Italy. We then analyzed the 87Sr/86Sr ratios of eight exceptionally well-preserved archaeological hair specimens associated with human mummies from Roccapelago. Trace elements were analyzed by LA-ICP-MS on single-hair specimens to check the preservation of the archaeological samples. Results: The strontium isotope composition of modern human hair varies from 0.7087 to 0.7093. The 87Sr/86Sr ratios of the Roccapelago hair strands range from 0.7082 to 0.7137, with an average of 0.7093 ± 0.0031 (2σ), revealing also intra-individual differences in isotopic composition along the length of the hair shaft. Data were compared with local archaeological rodent bones and teeth and with published isotopic values of water and outcropping rocks. Trace element abundances of archaeological and modern human hair are similarly low in terms of Rare Earth Element (REE) and metal contents, in particular after HNO3 leaching. Discussion: The variable modern human hair 87Sr/86Sr ratios show that high-resolution hair sampling tracks the movements of this individual between the two continents. The Sr isotope composition of the mummy hair is consistent with sub-annual human movements from Roccapelago to an area with different 87Sr/86Sr ratios. Historical sources indicate that individuals from Roccapelago travelled with their herds to Tuscany for transhumance pastoralism practices. The high radiogenic 87Sr/86Sr ratios (>0.71) found in some of the hair are possibly consistent with the Tuscan Magmatic Province and the Tuscan Metamorphic Complex isotope signature. To our knowledge, this is the first study in an archaeological context where the Sr isotope evidence of mobility is corroborated by historical documents.
2018
- Unravelling biocultural population structure in 4th/3rd century BC Monterenzio Vecchio (Bologna, Italy) through a comparative analysis of strontium isotopes, non-metric dental evidence, and funerary practices
[Articolo su rivista]
Sorrentino, Rita; Bortolini, Eugenio; Lugli, Federico; Mancuso, Giuseppe; Buti, Laura; Oxilia, Gregorio; Vazzana, Antonino; Figus, Carla; Serrangeli Maria, Cristina; Margherita, Cristiana; Penzo, Annachiara; Gruppioni, Giorgio; Gottarelli, Antonio; Jochum Klaus, Peter; Belcastro Maria, Giovanna; Cipriani, Anna; Feeney Robin, N. M.; Benazzi, Stefano
abstract
The 4th century BC marks the main entrance of Celtic populations in northern Italy. Their arrival has been suggested based on the presence of Celtic customs in Etruscan mortuary contexts, yet up to now few bioarchaeological data have been examined to support or reject the arrival of these newcomers. Here we use strontium isotopes, non-metric dental traits and funerary patterns to unravel the biocultural structure of the necropolis of Monterenzio Vecchio (Bologna, Italy). Subsamples of our total sample of 38 individuals were analyzed based on different criteria characterizing the following analyses: 1) strontium isotope analysis to investigate migratory patterns and provenance; 2) non-metric dental traits to establish biological relationships between Monterenzio Vecchio, 13 Italian Iron age necropolises and three continental and non-continental Celtic necropolises; 3) grave goods which were statistically explored to detect possible patterns of cultural variability. The strontium isotopes results indicate the presence of local and non-local individuals, with some revealing patterns of mobility. The dental morphology reveals an affinity between Monterenzio Vecchio and Iron Age Italian samples. However, when the Monterenzio Vecchio sample is separated by isotopic results into locals and non-locals, the latter share affinity with the sample of non-continental Celts from Yorkshire (UK). Moreover, systematic analyses demonstrate that ethnic background does not retain measurable impact on the distribution of funerary elements. Our results confirm the migration of Celtic populations in Monterenzio as archaeologically hypothesized on the basis of the grave goods, followed by a high degree of cultural admixture between exogenous and endogenous traits. This contribution shows that combining different methods offers a more comprehensive perspective for the exploration of biocultural processes in past and present populations.
2017
- A global reference database of crowdsourced cropland data collected using the Geo-Wiki platform
[Articolo su rivista]
Laso Bayas, Juan Carlos; Lesiv, Myroslava; Waldner, François; Schucknecht, Anne; Duerauer, Martina; See, Linda; Fritz, Steffen; Fraisl, Dilek; Moorthy, Inian; Mccallum, Ian; Perger, Christoph; Danylo, Olha; Defourny, Pierre; Gallego, Javier; Gilliams, Sven; Akhtar, Ibrar Ul Hassan; Baishya, Swarup Jyoti; Baruah, Mrinal; Bungnamei, Khangsembou; Campos, Alfredo; Changkakati, Trishna; Cipriani, Anna; Das, Krishna; Das, Keemee; Das, Inamani; Davis, Kyle Frankel; Hazarika, Purabi; Johnson, Brian Alan; Malek, Ziga; Molinari, Monia Elisa; Panging, Kripal; Pawe, Chandra Kant; Pérez-Hoyos, Ana; Sahariah, Parag Kumar; Sahariah, Dhrubajyoti; Saikia, Anup; Saikia, Meghna; Schlesinger, Peter; Seidacaru, Elena; Singha, Kuleswar; Wilson, John W.
abstract
A global reference data set on cropland was collected through a crowdsourcing campaign using the Geo-Wiki crowdsourcing tool. The campaign lasted three weeks, with over 80 participants from around the world reviewing almost 36,000 sample units, focussing on cropland identification. For quality assessment purposes, two additional data sets are provided. The first is a control set of 1,793 sample locations validated by students trained in satellite image interpretation. This data set was used to assess the quality of the crowd as the campaign progressed. The second data set contains 60 expert validations for additional evaluation of the quality of the contributions. All data sets are split into two parts: the first part shows all areas classified as cropland and the second part shows cropland average per location and user. After further processing, the data presented here might be suitable to validate and compare medium and high resolution cropland maps generated using remote sensing. These could also be used to train classification algorithms for developing new maps of land cover and cropland extent.
2017
- C4-plant foraging in Northern Italy: stable isotopes, Sr/Ca and Ba/Ca data of human osteological samples from Roccapelago (16th–18th century AD)
[Articolo su rivista]
Lugli, Federico; Brunelli, Daniele; Cipriani, Anna; Bosi, Giovanna
abstract
Human osteological samples (n = 23) taken from different anatomical parts of 11 individuals from the early modern (16th–18th century AD) site of Roccapelago (Modena, Italy) were systematically analysed for δ13C, δ15N and trace elements to investigate their diet. δ13C and δ15N correlate and show a high variability between individuals, attesting to the dietary contribution of C4 plants. This is supported by pollen analysis of the burial site samples, which revealed the presence of maize. δ15N correlates with Sr/Ca, suggesting that the main protein source could have been milk and dairy. We therefore interpret the strong correlation between δ13C and δ15N as evidence for C4-plant foraging practice and the exploitation of livestock for meat and milk, combined with possible direct intake of C4 plants. The Roccapelago site represents an important case study to track the evolution of the post-medieval diet and the introduction of maize cultivation in southern Europe, as also attested by historical sources.
2017
- Commentary on “Analyses of human dentine and tooth enamel by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to study the diet of medieval Muslim individuals from Tauste (Spain)” by Guede et al. 2017, Microchemical Journal 130, 287–294
[Articolo su rivista]
Lugli, Federico; Cipriani, Anna
abstract
The study of trace element (TE) distribution within human and animal teeth is crucial to decrypt information about their diet, ecology and behaviours in the past. Thanks to several efforts TE applications have spread also to the study of modern environments, with repercussions in medicine and forensic contexts. However, the use of TE analysis to infer eating habits of our ancestors has been used for decades without the proper theoretical basis. After the paper of Ezzo Ezzo (1994) that demonstrated the non-validity in the use of bioessential TE elements in bones and teeth as palaeodiet markers this trend has decreased. However, still some recent papers continue to ignore that portion of the literature that strongly contrasts the use of TE analysis for palaeodiet. With this commentary, we would like to share our remarks on the paper of Guede et al. Guede et al. (2017), where, in our opinion, there is a lack of literature review and thus a misinterpretation of the TE dataset.
2017
- In situ high spatial resolution 87Sr/86Sr ratio determination of two Middle Pleistocene (c.a. 580 ka) Stephanorhinus hundsheimensis teeth by LA–MC–ICP–MS
[Articolo su rivista]
Lugli, Federico; Cipriani, Anna; Peretto, Carlo; Mazzucchelli, Maurizio; Brunelli, Daniele
abstract
Bone and tooth tissues are important biological archives to study eating habits and provenance of ancient humans and animals. By taking advantage of the high spatial resolution offered by the Laser Ablation Multi Collector Inductively Coupled Plasma Mass Spectrometry (LA–MC–ICPMS) technique, we investigated the 87Sr/86Sr intra-tooth variability of two Stephanorhinus hundsheimensis tooth fragments from the Middle Pleistocene site of Isernia La Pineta. We detected significant Sr isotopes variability within the rhinos tooth enamel (enamel average ±2 sigma: sample RH–IS30 0.70951 ± 0.00014; sample RH–IS260.70976 ± 0.00015) with values higher than the “local”87Sr/86Sr ratio (dentine average ±2 sigma: sample RH–IS30 0.70918 ± 0.00013; sample RH–IS26 0.70934 ± 0.00009). This is likely linked to a different water and food intake with a Sr isotopic signature similar to volcanic soils nearby (Roccamonfina: from 0.7093 to 0.7100; Colli Albani: >0.7100) and supports the idea that the Stephanorhinus hundsheimensis species moved around seasonally. The improvement of non-destructive, accurate and precise analytical methods to decrypt the information hidden within bone and tooth hard tissues of archeological material is crucial to unravel critical questions about evolution, migration and ecology of human and animals. We have successfully took upon this challenge using three matrix-matched reference materials, with variable Sr concentration (c.a. 100–1000 ppm), to correct unresolved interferences arising from LA analyses.
2017
- Mantle-Crust Isotopic Relationships along Mid Ocean Ridges: Constraints from the Analysis of Time Series
[Abstract in Atti di Convegno]
Cipriani, Anna; Brunelli, Daniele
abstract
Isotopic relationships between parent mantle and
daughter MORBs have been used to reveal the composite
nature of the source tracking the missing components in their
isotopic fingerprints. An opportunity to address this issue is
given by temporal sections of single ridge segments where
MORB and residual parent mantle peridotites can be assessed
together. The possibility has been offered by the flexured and
uplifted lithospheric slab that exposes, on the sea floor along
a seafloor spreading flow line, a zero to 26 Ma relatively
undisturbed lithospheric section (Vema Lithospheric Section
or VLS) generated at the 80 km long Mid Atlantic ridge
segment (EMAR) at 11°N.
Temporal variations of the Nd isotopic composition of
crustal basalts and parental mantle along the VLS reveal a
large dispersion of residual isotopic composition with respect
to the melt products. Equilibration with partially mixed melts
can account for the observed relationships in the mantle
rocks. The mean MORB isotopic composition and the
average composition of the residues do not match because of
the preferential extraction of the low-melting component. The
compositional difference in both isotopic and elemental
distribution is a function of the average degree of melting of
the mantle. This observation can only be justified by
progressive melting of composite lithologies where mantle
potential temperature and amount of dispersed low-melting
lithologies control the relative extent of melting of the mantle
host and that of the dispersed heterogeneities resulting in
differential fractions of mixed melts in the final products.
This observation is confirmed by global correlations in Nd
isotopes and chemical indicators of degree of melting from
other portions of the mid ocean ridge system.
2017
- Melt-Rock Interaction at Mantle Conditions: Evidences from Finero Gabbroic Dykes
[Abstract in Atti di Convegno]
Giovanardi, Tommaso; Cipriani, Anna; Lugli, Federico; Morishita, Tomoaki; Zanetti, Alberto; Mazzucchelli, Maurizio
abstract
The Finero Phlogopite-Peridotite (FPP) is a worldwide
famous mantle massif recrystallized through several events of
melt migrations. These events have enriched the FPP in
hydrous phases and crustal components and have been
commonly interpreted as related to a subduction/post
orogenic geodynamic setting. The last of these metasomatic
events has produced composite sapphirine-bearing gabbroic
dykes, interpreted as the result of the interaction of
channelized migrating melts with the host rock in a two-steps
intrusion process. In the first step, the melt reacted with the
FPP rocks and evolved by fractional crystallization of
amphibole cumulates. In the second step, the evolved melt
reacted with the first cumulates producing magmatic
sapphirine and segregating plagioclase-rich bands containing
abundant apatites at the nucleus of the dike. New data
suggest, however, a more complex evolution.
New O and in situ Sr isotopes on minerals suggest that
the gabbroic dykes have evolved from melt(s) that
progressively were contaminated by the interaction with the
FPP rocks during its fractionation. The δ18O increases from
5.81‰ in orthopyroxenes at the dykes border to ~6.90‰ in
cumulitic amphiboles and 8.60‰ in plagioclases. The
87Sr/86Sr values for plagioclase and coexisting apatite show
isotopic disequilibrium between the two phases (plagioclases
at 0.70474 ± 0.00033, n=23, and apatites at 0.70369 ±
0.00025, n=6). These isotopic variations could be explained
with an AFC-like process between mantle-derived melt(s) and
a crustal-enriched host (the FPP).
In situ Sr isotope analyses were performed at the CIGS
laboratory of the Università di Modena e Reggio Emilia using
a Thermo Fisher Scientific Neptune™ coupled to a 213 nm
Nd:YAG laser ablation system (New Wave Research™).
During the analytical sessions a new in house plagioclase
reference material for Rb-Sr systematic, named BC84, has
been successfully tested and used.
2017
- Miocene phosphatic hardgrounds of the Mediterranean and their biotic assemblage: new insights from the "Aturia level" of the Salento Peninsula (S. Italy)
[Abstract in Atti di Convegno]
Vescogni, Alessandro; Bosellini, Francesca Romana; Vertino, Agostina; Harzhauser, Mathias; Mandic, Oleg; Cipriani, Anna; Conti, Stefano; Remitti, Francesca
abstract
From the late Oligocene to the late Miocene, the central Mediterranean area was interested by an
extensive deposition of phosphate-rich sediments. They are usually represented by 10-20 cm thick,
sub-horizontal hardgrounds, made of phosphatic sediments arranged into thin layers separated by
erosion surfaces. Macrofossils are very abundant, their assemblage composed of colonial and solitary
corals, molluscs, echinoderms, brachiopods, bryozoans and fish teeth.
In the past decades, the Mediterranean phosphatic deposits have been the subject of several studies,
mainly aimed to understand their depositional processes and the mechanisms leading to
phosphogenesis. In particular, the formation of these sediments has been recently interpreted as
associated to the occurrence of a complex system of upwelling currents, flowing into the central
Mediterranean from the deeper, eastern region of the basin. However, most of the contributions
mainly relies on stratigraphic, sedimentary and geochemical features, whereas the macrofossil
assemblage, despite its abundance and diversity, has never been analyzed in detail. The main goal of
this study is thus a thorough investigation, mainly from a palaeontological/palaeoecological
perspective, of the phosphatic deposits of the Salento Peninsula (named “Aturia” level). Special
attention is given to the coral and mollusc associations, particularly sensitive to changes in the main
environmental stressors and representing the most abundant biotic components of the phosphatic
deposits.
The Salento Aturia level is up to 25 cm in thickness and made of several phosphatic layers separated
by erosion surfaces. Microstratigraphic and microfacies analyses allow to identify two distinct facies.
A coral rudstone, about 7-10 cm thick, constitutes the base of the hardground, while on the top lies a
detrital rudstone, made of the succession of thinner layers mainly composed of phosphatic fragments.
Most of the macrofossils are concentrated within the coral rudstone and particularly abundant are
corals, associated to molluscs and to a lesser amount to brachiopods, echinoderms, bryozoans,
serpulids and fish teeth.
The coral assemblage is composed at least by 16 taxa belonging to 4 families, represented in order of
2017
- New U-Pb SHRIMP-II zircon intrusion ages of the Cana Brava and Barro Alto layered complexes, central Brazil: constraints on the genesis and evolution of the Tonian Goias Stratiform Complex
[Articolo su rivista]
Giovanardi, Tommaso; Girardi, Vicente A. V.; Correia, Ciro T.; Tassinari, Colombo C. G.; Sato, Kei; Cipriani, Anna; Mazzucchelli, Maurizio
abstract
The Cana Brava, Niquelândia and Barro Alto complexes (Goiás, central Brazil) are three of the largest mafic-ultramafic layered complexes in the world and their origin has been a matter of debate for several decades. One hypothesis suggests that Niquelândia and Barro Alto were both formed by two distinct igneous events at 1.3 Ga and at 790Ma and were later overlapped during tectonic exhumation at 650 Ma; according to this reconstruction Cana Brava belongs to the youngest intrusion at 790 Ma. A second hypothesis suggests that the three complexes formed during the same event. Here we provide new U-Pb SHRIMP-II zircon ages for the Cana Brava and Barro Alto complexes, constraining their intrusion age to the Neoproterozoic (between 770 and 800 Ma), coeval with Niquelândia. A review of new and literature ages indicate that these complexes formed during a single igneous event andwere notmodified by regional metamorphism.We propose that the complexes represent fragments of the larger Tonian Goiás Stratiform Complex, which was likely part of a back-arc environment connected to the formation of the GoiásMagmatic Arc at about 790Ma, later disrupted and accreted to the São Francisco craton.
2017
- Pyroxenites sow discord between
parent mantle and daughter MORB
[Abstract in Atti di Convegno]
Brunelli, Daniele; Cipriani, Anna
abstract
Mantle rocks and MORBs sampled along the 26 Ma
record of the Vema Lithospheric Section or VLS (Mid
Atlantic 11°N) reveal a profound divergence between parent
and daughter rocks in their compositional evolution. Finding
the cause of this discordance requires comparing the
evolution through time of the extent of melting with the
produced crustal thickness and changes in the chemistry and
isotopic composition of the sampled rocks. Mantle rocks
show a progressive increase of their degree of melting during
time, as if the potential temperature had increased in the last
26 Ma. However, plate kinematics reveal a significant
decrease of the spreading rate that should sensibly lower the
average degree of melting. MORB inferred degree of melting
decreases through time while their isotopic fingerprint
becomes more depleted. The observed variations can be
reconciled by considering that a variable amount of lowmelting
lithologies entered the melting region. The observed
decoupling of the degree of melting of mantle and MORB is
attributed to the effect of undercooling exerted by lowmelting
heterogeneities due to heat diffusion before the host
mantle starts melting itself. The observed temporal evolution
is matched by a decreasing amount of low-melting,
isotopically enriched, lithologies (pyroxenites) dispersed in a
DMM-type host mantle. Approaching the present day setting,
the amount of pyroxenites has become negligible restoring
harmony between parent mantle and MORB daughters in
terms of degree of melting and integrated melt production.
This observation can be extended to the entire MOR
system revealing the sensitivity of the spreading system to the
amount of low-melting lithologies dispersed in the depleted
mantle host. At limit conditions of the mantle potential
temperature, heat diffusion into the low-solidus melting
lithology prevents the host mantle from reaching its solidus.
2017
- Strontium Isotope MC-ICP-MS Analysis of Hair Strands from Human Mummies: Transhumance Pastoralism of Early-Modern Individuals between Northern and Central Italy
[Abstract in Atti di Convegno]
Lugli, Federico; Cipriani, Anna; Tavaglione, Valentina; Traversari, Mirko; Benazzi, Stefano
abstract
Mammal hair is formed by a scleroprotein, namely
keratin, composed by some major elements (C, N, H, O, S),
but including also trace elements such as Sr, Pb, Fe, K, Na
and Ca. The latter are fixed through diet and exposure to
exogenous sources, mainly water and air. Given that the
average human scalp hair growth is ~1 cm/month, timeresolved
hair sampling yields information about a specific
period, reflecting the elemental and isotopic composition of
the diet and environment at that time. The 87Sr/86Sr ratio of
mammal tissues is generally directly correlated to the local
bioavailable strontium, providing the chance to reconstruct
the individual movements in a given time interval.
In this work, we developed our protocol to analyse low-Sr
concentration mammal hairs for their 87Sr/86Sr ratio by
Neptune MC-ICP-MS. We tested the method on a modern
individual who traveled cyclically between Italy and Brazil.
Hair strands were sampled with a time resolution of 1 to 2
months, yielding time resolved isotopic variations from the
highest radiogenic ratios of the São Paulo area to the lower
ones of Modena waters. Thus, the Sr analysis of hair has been
applied to human mummies (Roccapelago, Modena, 16th-18th
cent.). Hair strands were cut in several sub-samples with
different length (time-resolution) in relation to the amount of
available material. The best achieved time-resolution was of 3
months in a 12-cm-long strand. These samples revealed
cyclical human movements from Roccapelago to the high
radiogenic area of the Tuscan Magmatic Province. Historical
documents attest a high frequency of human seasonal travels
to Tuscany, up to the Grosseto area, likely linked to the
exploitation of transhumance pastoralism.
2017
- Suspected limited mobility of a Middle Pleistocene woman from Southern Italy: strontium isotopes of a human deciduous tooth
[Articolo su rivista]
Lugli, Federico; Cipriani, Anna; Arnaud, Julie; Arzarello, Marta; Peretto, Carlo; Benazzi, Stefano
abstract
We present the Sr isotopic composition of enamel of the most ancient deciduous tooth ever discovered in Italy to assess human mobility in Middle Pleistocene. Reconstructing ancient mobility is crucial for understanding human strategy at exploiting temporally and spatially patchy resources, with most studies focusing on indirect evidences, ultimately affecting our interpretation on hominin territoriality and energetic costs invested by hominin groups. Here, we use the high spatial resolution and micro-destructivity options offered by the Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry technique, to determine the (87)Sr/ (86)Sr intra-tooth variability of a human deciduous incisor from the Middle Pleistocene layers of the Isernia La Pineta site (Italy). We compared these data with the Sr isotopic signature of local micro-mammals, the broadest home-range of the macro-mammals and with modern plant samples. Our study reveals that while macro-mammals have possibly migrated through the landscape for up to 50 km, the pregnant woman from Isernia was probably local, given that the isotopic ratio of the enamel falls within the local range and is comparable with the signature of the local plants in a radius of 10 km. This is the first case study of Sr isotopic composition determination in such ancient deciduous tooth.
2017
- Timing of transverse ridge uplift along the Vema transform (Central Atlantic)
[Articolo su rivista]
Gasperini, Luca; Bonatti, Enrico; Borsetti, Anna Maria; Capotondi, Lucilla; Cipriani, Anna; Negri, Alessandra
abstract
Transverse ridges are large topographic anomalies running adjacent to slow-slip oceanic transforms. They form due to different processes, including thermal stresses, hydration-dehydration of peridotites, non-linear viscoelastic rheology of the oceanic crust and vertical tectonic motions of lithospheric slivers induced by changes in ridge/transform geometry, causing transpression and/or transtension along the transform boundary. A prominent transverse ridge on the southern side of the Vema transform (Central Atlantic) rose probably between 12 and 10 Ma along the entire length (≈ 320 km) of the transform, exposing a relatively undisturbed section of oceanic lithosphere. We used pelagic limestones encrusting serpentinized peridotites sampled from the lower slopes of the uplifted lithospheric section to date this uplift and define mechanisms of its emplacement. Ages were obtained both by micropaleontology (foraminifera and nannofossils) and by 87Sr/86Sr isotope ratios. No ages older than ≈ 12 Ma were obtained, even in samples recovered at sites with crustal ages (determined by magnetic anomalies) well over 12 Ma; on the other side, ages as young as 5.6–8.3 Ma were found in clusters of samples collected from the eastern part of the transverse ridge, probably due to mass-wasting episodes that rejuvenated the substratum. These results support the hypothesis that the Vema Transverse Ridge rose between 12 and 10 Ma due to flexural uplift related to transtension along the transform, in line with a general model whereby transverse ridges rise during discrete events as a consequence of changes in ridge-transform geometry.
2016
- In situ 87Sr/86Sr LA-MC-ICPMS on biogenic apatites: a matrix-matched standard correction approach
[Abstract in Atti di Convegno]
Lugli, Federico; Cipriani, Anna; Mazzucchelli, Maurizio; Sforna, MARIE CATHERINE; Brunelli, Daniele
abstract
Strontium isotope ratios are a strong tool to study ancient hominin and animal migrations, hence the increasing need to have a simple, fast and microdestructive analytical technique to obtain accurate and precise 87Sr/86Sr ratios of precious tooth enamel and bone tissue. The traditional analysis by the TIMS or MC-ICPMS tecniques requires sample dissolution; therefore, several LA-MC-ICPMS methods have been developed to prevent sample destruction, particularly for prehistoric human teeth. Instrumental calibration on human enamel is difficult because of the typical low-Sr concentration and analytical interferences. In fact, the methodology for data reduction of in situ Sr isotopes of biogenic apatite is largely debated in the literature [e.g. 1, 2]. While monoatomic interferences (Kr, Rb, REE2+) are routinely corrected, the correction of polyatomic interferences (CaCa, CaAr and 40Ca31P16O) are challenging. In particular, the CaPO molecule strongly interferes on mass 87, hindering the achievement of precise and accurate 87Sr/86Sr ratios. Following on the work of Horstwood et al. (2008), we developed a method based on the concurrent analyses of multiple matrix-matched standard materials. We show how the linear regression of 87Sr/86Sr accuracy vs. 1/88Sr of at least three standards allows correction of this interference. During each analytical session, we analyse our four in-house matrix-matched standards (a human tooth, a bovine tooth, a swine tooth and a shark tooth) covering a wide range of Sr concentrations (from c.a. 100 ppm of the human tooth to the 1000 ppm of the shark tooth). A daily CaPO model is then built to predict the expected accuracy of the analysis. This correction gives an external reproducibility to the 4th decimal digit (e.g. 2σ-human enamel = 0.00047; c.a. 100 ppm) and an accuracy between the 4th and the 5th decimal digit when applied to analyses with a laser spot sizes of 100μm and a linear dynamic ablation pattern. Monitoring of the CaPO molecule formation during analysis is also achieved by performing several high resolution mass scans.
2016
- Origin of the DUPAL anomaly in mantle xenoliths of Patagonia (Argentina) and geodynamic consequences
[Articolo su rivista]
Mazzucchelli, Maurizio; Cipriani, Anna; Hémond, Christophe; Zanetti, Alberto; Bertotto, Gustavo Walter; Alberto, C. i. n. g. o. l. a. n. i. Carlos
abstract
The sub-continental lithospheric mantle of South America has been known for some time to carry the DUPAL isotope anomaly as seen in volcanics from the Paraná volcanic province. However, this has not allowed discriminating whether the DUPAL anomaly is a primary feature of the mantle source or acquired during the upwelling and emplacement of the primary magmas. We discovered mantle xenoliths from the Tres Lagos location in Patagonia that carry evidence of percolation by metasomatic melts that imparted the DUPAL isotope anomaly signature. We discuss a model that requires four isotope components (LCC, EM2, HIMU and DM) to account for the Sr, Nd and Pb isotope variability of our samples. We propose that upwelling of hot astenosphere during the Miocene could have triggered the melting of the LCC and EM2 components carrying the DUPAL anomaly, previously entrained in the subcontinental mantle by subduction. These ascending melts would have then metasomatised the local SCLM characterised by DMM and HIMU geochemical affinity generating the hybrid DUPAL-bearing mantle sampled by the Tres Lagos xenoliths.
2016
- PRELIMINARY U-Pb LA-ICPMS ZIRCON ANALYSES FROM THE GOIAS COMPLEXES: SHRIMP COMPARISON AND INTRUSION AGE
[Abstract in Rivista]
Lugli, Federico; Giovanardi, Tommaso; Girardi, V. A. V.; Correla, C. T.; Tassinari, C. C. G.; Sinigoi, S.; Cipriani, Anna; Mazzucchelli, Maurizio
abstract
Cana Brava, Niquelàndia and Barro Alto are three mafic-ultramafic layered intrusions (from N to S) which form a - 350 km, NNE-trend belt within the Brasilia Belt (Goiés state, Brazil). Presently, their intrusion ages and geologica! evolution are stili debated. The Niquelàndia and Barro Alto complexes are forrned by two main sequences: the upper sequence and the lower one. Some authors suggest that the two sequences represent two separate intrusions: the upper sequence would be a Mesoproterozoic intrusion at - 1.3 Ga, whereas the lower sequence a Neoproterozic one at - 790 Ma. According to this interpretation, the two sequences were re-crystallized by Neoproterozoic metamorphism and exhumed and juxtaposed during the Brazilian event of formation of the Gondwana continent. Another model suggests that the two sequences are part of the same intrusion, which occurred during the Neoproterozoic and was exhumed during the Brazilian event. New U-Pb SHRIMP-II zircon analyses were perforrned at the Universidade de Sào Paulo from samples from Cana Brava and Barro Alto, the two least-known complexes in order to clarify the sequence of events that led to their forrnation. Analyses were then replicated at the CIGS of the Università di Modena e Reggio Emilia using a X Series" quadrupole ICP-MS coupled with a New Wave UP-213 Nd:YAG laser ablation system. Zircons were sampled through a 40 micron spot (static mode), using a He flux of 0.6 l/min, with an energy density of - 6 J/cm2. Daily instrument calibration was perforrned with the NIST 610 standard, monitoring also the oxide production rate {232Th160/232Th << 0.01 %). Laser-induced elemental fractionation was corrected by repeated analyses of the standard zircon TEMORA2 (Black et al., 2004). A secondary reference materia! (zircon CZ3) was used to check the precision and accuracy of the corrections. Our LA-ICP-MS data are preliminary, but very promising being the accuracy of the measured ratio within the SHRIMP variability. We are currently working to improve the precision of our methodology, which however is now comparable with literature LA-ICP-MS data (propagated 2SE - 2-6%; Horstwood et al., 2008). Overall, the isotopic data of Cana Brava and Barro Alto complexes previde for a coeval Neoproterozoic intrusion age at - 790 Ma. These ages are consistent with those reported in literature for Niquelàndia. Mesoproterozoic ages, consistent with the forrnation age of the metavolcanic-metasedimentary sequence in magmatic contaci with the complexes, were found in inherited zircon cores. Our data clearly show that the Goiàs complexes are formed by single bodies intruded during the Neoproterozoic at -790 Ma and that the hypothesis of two separate intrusions juxtaposed by tectonic must
be discarded.
2016
- Pyroxenite Layers in the Northern Apennines’ Upper Mantle (Italy)—Generation by Pyroxenite Melting and Melt Infiltration
[Articolo su rivista]
Borghini, Giulio; Rampone, Elisabetta; Zanetti, Alberto; Class, Cornelia; Cipriani, Anna; Hofmann, Albrecht W.; Goldstein, Steven L.
abstract
Pyroxenite layers embedded within peridotite represent widespread lithological mantle heterogeneities and are potential components in the mantle source of many oceanic basalts. They can be generated by a variety of magmatic and metamorphic processes. However, in most natural samples (especially in ultramafic massifs), their primary characteristics are partially or completely erased by later processes (e.g. metamorphism, metasomatism or partial melting). Here we investigate a suite of pyroxenites from the External Liguride Jurassic ophiolites (Northern Apennines, Italy). These are spinel-bearing websterites and clinopyroxenites, partially recrystallized under plagioclase-facies conditions, and occur as centimetre-scale layers parallel to the tectonite foliation of their host peridotites. The pyroxenites have bulk-rock Mg-numbers from 74 to 88 and display rather constant light rare earth element (LREE) depletion relative to middle REE (MREE) (LaN/SmN = 0·15–0·35), but variable MREE–heavy REE (HREE) fractionation, with some having markedly positive HREE slopes (SmN/YbN = 0·30–0·96). The HREE enrichment, coupled with high Zr and Sc contents in clinopyroxene porphyroclasts from spinel-bearing domains, provides strong evidence that garnet was present in the precursor mineral assemblages. Mass-balance calculations suggest that the pyroxenites originally contained up to about 40 vol. % garnet, indicating that they originated by segregation of melts at relatively high pressure (P > 1·5 GPa). The parental melts of the pyroxenites have reacted to some extent with the host peridotite during mantle infiltration. Lack of olivine in the primary mineral assemblage and the presence of orthopyroxene-rich rims along the contact with the wall-rock peridotites suggest that the pyroxenites crystallized from silica-rich melts. These probably had REE patterns and Sr–Nd isotope compositions similar to those of enriched mid-ocean ridge basalt. We propose that the pyroxenites originated from melts derived from a hybrid eclogite-bearing peridotite source, which subsequently reacted with their host peridotite to form ‘secondary pyroxenites’. The existence of such pyroxenites has been invoked in current models of basalt petrogenesis. During later decompression, the pyroxenites experienced recrystallization at spinel-facies conditions, at 1·2–1·5 GPa and minimum temperatures of 950–1000°C, and partial re-equilibration in the low-pressure plagioclase facies. The latter event is dated by internal Sm–Nd isochrons at 178 (±8) Ma and is associated with Mesozoic exhumation during extension of the Tethys lithosphere.
2016
- THE LARGE LAYERED GOIAS COMPLEXES: NEW U-Pb ANO PRELIMINARY Lu-Hf IN SITU ZIRCON ANALYSES FROM BARRO ALTO AND CANA BRAVA
[Abstract in Rivista]
Giovanardi, Tommaso; Lugli, Federico; Girardi, V. A. V.; Correla, C. T.; Tassinari, C. C. G.; Sinigoi, S.; Cipriani, Anna; Mazzucchelli, Maurizio
abstract
The large layered Goias complexes are three mafic-ultramafic layered intrusions which outcrop in a -350 km, NNE-trend bel! within the Brasilia Belt (centrai Brazil). Fom N lo S, they are: Cana Brava, Niquelllndia and Barro Alto. The intrusion age and geologica! hystory of these intrusions is stili presently debated. New U-Pb SHRIMP-II zircon analyses were perforrned in samples from Cana Brava and Barro Alto, the two poorest-known complexes among them, providing fora coeval Neoproterozoic intrusion age al -790 Ma of both complexes, consistent with literature ages for the Niquelandia complex. lnherited zircons with Mesoproterozoic ages are consistent with the formation age of the metavolcanic-metasedimentary sequences in magmatic contaci with these three complexes and suggest some degree of contamination of the complexes. This contamination in Niquelandia and Cana Brava is well known in the literature as revealed by bulk-rock Rb-Sr and Sm-Nd systematics. The two complexes show enrichment of the contamination in their gabbroic sequence with local enrichment where the crustal xenoliths are more abundant. Conversely, the upper pari of Niquelandia, mainly formed by anorthosite, is almost or totally uncontaminated. The Lu-Hf analyses on zircons from the Goiés complexes were perforrned during the instrument calibration of the Lu-Hf methodology al the laboratories of Centro lnterdipartimentale Grandi Strumenti al the Università di Modena e Reggio Emilia. The measurements were carried out using a Neptune MC-ICPMS coupled with a New Wave UP-213 laser ablation. The instrument was firstly calibrated on a standard solution and successively in situ analyses on complexes zircons were carried out together with CZ3 and TEMORA2 zircon standards. Mass bias and isobaric interference were corrected offiine using the lsotopeMaker free software of Zhang et al. (2015). Preliminary Lu-Hf in situ zircon data show negative EHf(t) values which are consistent with crustal contamination of the Barro Alto and Cana Brava parental melts as show by Rb-Sr and Sm-Nd in Cana Brava. The new Lu-Hf data, togheter with a review of literature data, show, for Barro Alto, a contamination similar to Niquelandia for the Rb-Sr and Sm-Nd systematics: zircons from the gabbroic sequence are contaminated, while zircons from the upper anorthosites are poorly contaminated. lnherited zircons commonly show positive EHf(t) values, which suggest mantle-derived melts for the magmatism of the metavolcanicmetasedimentary sequence.
2015
- Building a hybrid land cover maps with crowdsourcing and geographically weighted regression
[Articolo su rivista]
See, Linda; Schepaschenko, Dmitry; Lesiv, Myroslava; Mccallum, Ian; Fritz, Steffen; Comber, Alexis; Perger, Christoph; Schill, Christian; Zhao, Yuanyuan; Maus, Victor; Siraj, Muhammad Athar; Albrecht, Franziska; Cipriani, Anna; Vakolyuk, Mar'Yana; Garcia, Alfredo; Rabia, Ahmed; Singha, Kuleswar; Marcarini, Abel Alan; Kattenborn, Teja; Hazarika, Rubul; Schepaschenko, Maria; van der Velde, Marijn; Kraxner, Florian; Obersteiner, Michael
abstract
Land cover is of fundamental importance to many environmental applications and serves as critical baseline information for many large scale models e.g. in developing future scenarios of land use and climate change. Although there is an ongoing movement towards the development of higher resolution global land cover maps, medium resolution land cover products (e.g. GLC2000 and MODIS) are still very useful for modelling and assessment purposes. However, the current land cover products are not accurate enough for many applications so we need to develop approaches that can take existing land covers maps and produce a better overall product in a hybrid approach. This paper uses geographically weighted regression (GWR) and crowdsourced validation data from Geo-Wiki to create two hybrid global land cover maps that use medium resolution land cover products as an input. Two different methods were used: (a) the GWR was used to determine the best land cover product at each location; (b) the GWR was only used to determine the best land cover at those locations where all three land cover maps disagree, using the agreement of the land cover maps to determine land cover at the other cells. The results show that the hybrid land cover map developed using the first method resulted in a lower overall disagreement than the individual global land cover maps. The hybrid map produced by the second method was also better when compared to the GLC2000 and GlobCover but worse or similar in performance to the MODIS land cover product depending upon the metrics considered. The reason for this may be due to the use of the GLC2000 in the development of GlobCover, which may have resulted in areas where both maps agree with one another but not with MODIS, and where MODIS may in fact better represent land cover in those situations. These results serve to demonstrate that spatial analysis methods can be used to improve medium resolution global land cover information with existing products. © 2014 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS).
2015
- Discovering Past Gut Microbiomes Through Ngs Analysis: The Mummies Of Roccapelago (MO)
[Abstract in Atti di Convegno]
Cilli, E.; De Filippo, C.; Albanese, D.; Lugli, Federico; Sordo, M.; Viola, M. F.; Traversari, M.; Catalano, G.; Serventi, P.; De Fanti, S.; Quagliariello, A.; Labate, D.; Cipriani, Anna; Luiselli, D.; Gruppioni, G.
abstract
The gut microbiota plays a primary role in metabolism and immune response of host organisms. It is influenced by lifestyle, diet and environment but little is known about its ancestral state and evolution, especially in relation to past human dietary shifts, the impact of industrialization and the introduction of antibiotics. In the reconstruction of the ancestral state of gut microbiota, recent pioneering studies have focused on contemporary rural populations or ancient coprolites. This paper presents the first screening of microbiota by NGS technology from ancient human gut tissues. We collected samples from ten Roccapelago mummies (16th-18th c. AD) from different anatomical tissues (gut, skin, muscle). In addition, samples of soil and clothes were analyzed to detect environmental contamination. Paleodiet reconstruction by stable isotopes analysis (δ13C and δ15N) was performed on femurs and teeth. Moreover, information about diet, lifestyle and health were recovered from parish registers and historical documents. DNA was extracted with a silica-based protocol and amplicons of 16S rRNA gene (V3 region) were sequenced on 454/Roche obtaining an average of 10.059 reads per sample. The bioinformatic analysis using the MICCA pipeline reveals a consistent diversification between tissues (gut vs muscle vs skin), with an enrichment of Actinobacteria in gut samples (18%) in respect to muscle and skin samples, despite Clostridiales are represented in all tissues analyzed. Interestingly halophilic, Gram-positive bacteria from Staphylococcaceae (6%), are found in gut samples. Investigation of a potential physiological basis of this association may lead to new insights into the reconstruction of past gut microbiomes.
2015
- In situ strontium isotope analysis on biogenic apatite: the use of Laser Ablation and Multi Collector Inductively Coupled Plasma Mass Spectrometer (LA–MC–ICPMS) in anthropological research
[Abstract in Atti di Convegno]
Lugli, Federico; Cipriani, Anna; Reghizzi, Matteo; Brunelli, Daniele; Benazzi, Stefano
abstract
The use of LA–MC–ICPMS in anthropological research is an innovative approach for measuring strontium isotopic ratios of human enamel. This technique, due to its micro-destructivity, allows to exam 87Sr/86Sr on precious human remains, without the drawbacks of the dissolution method. Despite this advantage, the laser ablation technique (LA) is not without flaws, principally related to unavoidable analytical interferences. For these reasons, data obtained with the laser are usually less precise and accurate than data obtained with the classical dissolution method. In particular, problematic interferences are represented by 86Kr formed in the gas, by double-charged REE (Rare Earth Element), by 87Rb, and by other polyatomic isobaric interferences (i.e. 44Ca40Ar, 40Ca44Ca, 40Ca13P16O). In this work, we measured the Sr isotopic ratio of a shark tooth with both dissolution and LA method, to test the precision of the LA method. A shark tooth is a bio-apatite formed in a marine environment, thus its 87Sr/86Sr ratio reflects the modern marine ratio of ~0.7092. Our preliminary laser analyses show that we are able to reproduce the isotopic ratio of our shark tooth obtained by Sr chromatographic separation and HR–MC–ICPMS with a precision to the fourth decimal place and that this ratio reflects the modern sea water value. If confirmed by further studies, our preliminary results suggest that the LA technique is a reliable method to explore hominin movement and migrations.
2015
- In situ trace element analysis of human hard tissues by Laser Ablation ICP–MS
[Abstract in Atti di Convegno]
Lugli, Federico; Cipriani, Anna; Brunelli, Daniele; Giorgio, Gruppioni; Mazzucchelli, Maurizio
abstract
After the advent of the laser ablation system (LA), the analysis of micro-samples of hard materials has spread to many scientific fields (i.e. geology, engineering, archaeometry, anthropology). The Laser Ablation Coupled with a Mass Spectrometer (as in the LA–ICP–MS) allows to investigate any hard material at the scale of a few µms, for example, defining the elemental compositional profile of bone, teeth and nephroliths, measuring any element with an atomic mass between 2 and 255 amu (i.e. heavy metals as Pb, Cr, Cd, As, etc.). Moreover, one of the main advantages offered by LA, compared to more traditional techniques, is the drastic reduction of analytical time, because the sample is analysed as it is without chemical dissolution or separation of elements. In this work, we have tested and developed a routine to measure all trace elements in human bones and teeth with the LA–ICPMS housed at the University of Modena and Reggio Emilia. We analyse all trace element but we have focused here our attention on Zn and Pb, given their importance and significance in dentistry, human health and forensic pathology studies. We have then analyzed two human teeth, measuring their trace elements compositional profile and drawing conclusions on the health history of these two individuals. Materials and Methods. We analysed two human teeth (molar 1HT–R and premolar 2HT–R) sampled from two post-medieval mummies (Roccapelago, Modena, 16th – 18th cent.). The concentrations of Pb and Zn were measured in situ through a 213 nm Nd:YAG Laser Ablation system coupled to a quadrupole ICP–MS system (Thermo Fisher Scientific® X SeriesII). Before analysis, each sample was cut in half with a diamond low-speed wheel saw, to expose the inner parts of the tooth. Eighteen LA–spots (diameter 100 µm) were analysed along two profiles (n=10 sample 1HT–R; n=8 sample 2HT–R), exploring enamel and dentine. The elemental concentrations of our samples have been corrected through a calibration with NIST 1486 Bone Meal as a multi-element standard. To correct any matrix-related effect, the calcium concentration, measured with an ESEM Quanta 200, has been used as the internal standard. To ensure the accuracy of the method, a two-tailed t-test was performed on two certified elements of the standard. Statistical analysis shows no significant difference between expected and measured values (p<0.05; mean of 3 analyses). Results. The first tooth (1HT–R) shows a Zn concentration ranging from 230 in the outer enamel to 110 ppm in the inner primary dentine (x = 150 ± 38 ppm, 1σ) and, respectively, a Pb concentration ranging from 3 to 1 ppm (x = 2 ± 1 ppm, 1σ). From the outer enamel to the inner dentine, the second tooth (2HT–R) shows a Zn concentration ranging from 301 to 123 ppm (x = 177 ± 66 ppm, 1σ) and a Pb concentration ranging from 6 to 2 ppm (x = 3 ± 1 ppm, 1σ). Conclusions. Our results are in agreement with Pb and Zn profiles described in literature for human teeth (Humphrey et al. 2008). The concentrations of both elements tend to increase from the enamel-dentine junction (EDJ) to the enamel external surface and tend to decrease from the EDJ to the inner dentine. The Pb concentration of both samples is on average lower than the threshold of poisoning reported for human bones (5 ppm; Hess et al. 2013). The Zn concentrations are low, in particular in the outer enamel. As reported by Lynch (2011), this could be related to tooth wear or to the old age of the two individuals (~ 40 yr). The LA–ICP–MS is a non-destructive in–situ analytical technique, fundamental in forensic pathology and human health studies to measure the elemental composition of human hard tissue and in particular, in outlining the history of the tooth by trace element compositional profile from the inner to the outer portions of the tooth.
2015
- Mapping global cropland and field size
[Articolo su rivista]
Fritz, Steffen; See, Linda; Mccallum, Ian; You, Liangzhi; Bun, Andriy; Moltchanova, Elena; Duerauer, Martina; Albrecht, Fransizka; Schill, Christian; Perger, Christoph; Havlik, Petr; Mosnier, Aline; Thornton, Philip; Wood Sichra, Ulrike; Herrero, Mario; Beckerreshef, Inbal; Justice, Chris; Hansen, Matthew; Gong, Peng; Abdelaziz, Sheta; Cipriani, Anna; Cumani, Renato; Cecchi, Giuliano; Conchedda, Giulia; Ferreira, Stefanus; Gomez, Adriana; Haffani, Myriam; Kayitakire, Francois; Malanding, Jaiteh; Mueller, Rick; Newby, Terence; Nonguierm, Andre; Olusegun, Adeaga; Ortner, Simone; Rajak, D. Ram; Rocha, Jansle; Schepaschenko, Dmitry; Schepaschenko, Maria; Terekhov, Alexey; Tiangwa, Alex; Vancutsem, Christelle; Vintrou, Elodie; Wenbin, Wu; Van der Velde, Marijn; Dunwoody, Antonia; Kraxner, Florian; Obersteiner, Michael
abstract
A new 1 km global IIASA-IFPRI cropland percentage map for the baseline year 2005 has been developed which integrates a number of individual cropland maps at global to regional to national scales. The individual map products include existing global land cover maps such as GlobCover 2005 and MODIS v.5, regional maps such as AFRICOVER and national maps from mapping agencies and other organizations. The different products are ranked at the national level using crowdsourced data from Geo-Wiki to create a map that reflects the likelihood of cropland. Calibration with national and subnational crop statistics was then undertaken to distribute the cropland within each country and subnational unit. The new IIASA-IFPRI cropland product has been validated using very high-resolution satellite imagery via Geo-Wiki and has an overall accuracy of 82.4%. It has also been compared with the EarthStat cropland product and shows a lower root mean square error on an independent data set collected from Geo-Wiki. The first ever global field size map was produced at the same resolution as the IIASA-IFPRI cropland map based on interpolation of field size data collected via a Geo-Wiki crowdsourcing campaign. A validation exercise of the global field size map revealed satisfactory agreement with control data, particularly given the relatively modest size of the field size data set used to create the map. Both are critical inputs to global agricultural monitoring in the frame of GEOGLAM and will serve the global land modelling and integrated assessment community, in particular for improving land use models that require baseline cropland information. These products are freely available for downloading from the http://cropland.geo-wiki.org website.
2015
- Oceanization starts from below during continental rupturing in the Red Sea
[Abstract in Atti di Convegno]
Ligi, M.; Bonatti, E.; Bosworth, W; Cai, Y.; Cipriani, Anna; Palmiotto, P.; Ronca, S.; Sanfilippo, A.; Seyler, Monique
abstract
Oceanization starts from below during continental rupturing in the Red Sea
2015
- Oceanization starts from below during continental rupturing in the northern Red Sea
[Abstract in Atti di Convegno]
Ligi, Marco; Bonatti, Enrico; Bosworth, William; Cai, Yue; Cipriani, Anna; Palmiotto, Camilla; Rasul, Najeeb; Ronca, Sara; Sanfilippo, Alessio; Seyler, Monique; Nomani, S.; Alqutub, A. .
abstract
The role of magmatism in continental rupturing and in the birth of a new ocean is not well understood. Continental rupture can take place with intense and voluminous volcanism, as in the Southern Red Sea or in a relatively amagmatic mode, as in the Northern Red Sea. Mantle upwelling and melting may be affected by the south to north decreasing opening rate of the Red Sea and by the influence of the Afar plume, also decreasing from south to north. The tholeiitic basalts of the Red Sea spreading system contrast with the extensive Cenozoic basaltic lava fields of the western part of the Arabian peninsula that form one of the largest alkali basalt provinces in the world. In order to establish possible relationship between the Red Sea rift evolution and the western Saudi Arabia intraplate alkali volcanism, field work was carried out on Lunayyir, Ishara, al Kura and Khaybar volcanic fields. Collected samples cover a wide range of chemical diversity (from olivine basalt to trachyte) and span over a 20 Ma interval. We attempt a comparison of the geochemistry of igneous rocks from western Arabia dykes and volcanic fields with those from the Red Sea axis and from the islands of Zabargad and Brothers in the northern Red Sea, that represent basaltic melts injected into the thinned continental crust before continental rupturing and initiation of seafloor spreading. Gabbros drilled in the western Red Sea and exposed on the Brothers islands suggest that continental break up in the northern Red Sea, a relatively non-volcanic rift, is preceded by intrusion of oceanic-type basaltic melts that crystallize at progressively shallower crustal depths as rifting progresses towards continental break-up. A seismic reflection profile running across the central part of the southern Thetis basin shows a ~5 km wide reflector that marks the roof of a magma chamber located ~3.5 km below seafloor. The presence of a few kilometers deep subrift magma chamber soon after the initiation of oceanic spreading implies the crystallization of lower oceanic crust intrusives as a last step in a sequence of basaltic melt intrusion from pre-oceanic continental rifting to oceanic spreading. Thus oceanic crust accretion in the Red Sea rift starts at depth before continental break up, emplacement of oceanic basalt at the sea floor, and development of Vine-Matthews magnetic anomalies.
2015
- Signatures of residual melts, magmatic and seawater-derived fluids in oceanic lower-crust gabbro from the vema lithospheric section, central Atlantic
[Articolo su rivista]
Pertsev, Alexey N.; Aranovich, Leonid Y.; Prokofiev, Vsevolod Y.; Bortnikov, Nikolay S.; Cipriani, Anna; Simakin, Sergey S.; Borisovskiy, Sergey E.
abstract
We present new data on mineral assemblages, mineral chemistry (major and trace element compositions), and fluid inclusions to reconstruct the magmatic to hydrothermal history of gabbroic rocks dredged in association with serpentinized mantle peridotites from the tectonically exposed Vema lithospheric section (central Atlantic). Textural relations and mineral chemistry of the samples indicate a two-stage magmatic evolution, from an early coarse-grained pyroxene-plagioclase cumulate to overprinted assemblages, including interstitial Fe-Ti oxides and titanian hornblende. Titanian hornblende in the gabbros is a product of interaction of crystal aggregates with an evolved residual melt or with a late-magmatic aqueous fluid at 800-900°C. The different contribution of residual melt and magmatic aqueous fluid is inferred from the behaviour of incompatible elements and plagioclase composition. One gabbro sample shows features indicative of a later stage hydrothermal event: formation of Fe- and Cl-rich hornblende sealing fractures in plagioclase, olivine coronas at orthopyroxene-magnetite grain boundaries, plagioclase-hosted high-salinity fluid inclusions associated with local enrichment of plagioclase in anorthite and Sr, and local augite to diopside re-equilibration. These features record the interaction of gabbro with seawater-derived fluid at temperature up to about 600°C. The high-salinity inclusions and reducing hydrothermal reactions in the gabbro indicate that the fluid phase characteristics may have been acquired through a preceding lower-temperature (<500°C) interaction of seawater with mantle peridotite (serpentinization) followed by infiltration of the modified aqueous solution into the higher-temperature (about 600°C) gabbroic zone in a geodynamic environment of a slow-spreading ridge segment end. Compositional features of the hydrothermal fluid were: salinity 20-22 wt % (NaCl eq.), Ca/(Ca+Na) ≤ 0.12, and log fO2 = -19.6 to -18.8.
2015
- Stable isotope and in situ trace element analyses on human bone tissue (Roccapelago, 16th-18th cent.): preliminary inferences on diachronic change in eating habits and trace element reliability
[Abstract in Atti di Convegno]
Lugli, Federico; Brunelli, Daniele; Cipriani, Anna; Bosi, Giovanna; Gruppioni, G.
abstract
We measured trace elements and stable isotopes (C and N on collagen) on 19 samples, taken from different anatomical area of 7 individuals from the medieval site of Roccapelago (Modena): our attempt is to reconstruct the diet of these individuals and discuss the role of trace elements in palaeodiet. The good preservation of these bodies represents a unique chance to work on likely diagenesis-free archaeological human remains, to test the trustworthiness of trace element analyses. In fact, in the last decades, trace element reliability was questioned several times. We particularly focus our attention on magnesium, strontium and zinc. Our data set shows different eating habits for the studied individuals. While collagen of the samples dated at 16th century yields typical values of a C3-plant based diet, collagen of samples dated at 18th cent yields higher values of both δ13C and δ15N, probably linked to an higher trophic level and to a shift toward a C4-environment. Similarly, Sr and Mg show the same increment in individuals of 18th cent, while Zn does not show any significant variation. The latter is quite discussed in the scientific literature and has been commonly used as a marker for a protein-rich diet. Our lack of correlation between Zn and stable isotopes (especially N) confirms the uselessness of this element in palaeodiet reconstruction. Geochemical data are also corroborated by the botanical evidence of maize presence (C4 plant) and by historical sources that attest the presence of maize in Emilia-Romagna during 18th century.
2015
- The Red Sea: Birth of an Ocean
[Capitolo/Saggio]
Bonatti, Enrico; Cipriani, Anna; Lupi, Luca
abstract
Nowhere on the present-day Earth can the transition from a continental to an oceanic rift be observed and studied better than in the Red Sea region, where three rifts in different stages of evolution meet in a triple point located in the Afar region. A thermal and/or compositional mantle plume may have risen from the upper mantle below Afar already at ~30 Ma, and may have triggered, at least in part, the rifting process. The axial area of the rifts is marked by intense seismicity. While the East African is a fully continental rift, the Gulf of Aden rift experienced oceanic crust accretion between Arabia and Somalia starting already at 17 Ma with a progressive westward propagation that impacted against Africa in the Afar Triangle starting at <1 Ma. The axial zone of oceanic crustal accretion in the Gulf of Aden is segmented by several small (<30 km) offsets, including two major transform-fracture zones, the Socotra (offset ~50 km) and the Alula-Fartak (offset 180 km). Spreading is asymmetric, faster in the northern (Arabia) side (11–13 mm/a) than in the southern (Somalia) side (8 mm/a). The Afar Triangle is a topographically depressed region, located between the continental blocks of Nubia, Somalia, and the Danakil Alps, that separate it from the southern Red Sea. It is an area of thin crust, seismicity related to extension, and intense intrusive and extrusive, mostly basaltic, magmatism. Intrusive basaltic magmatism appears to be important in triggering the rifting process in Afar. Northern Afar displays basaltic ranges oriented parallel to the axis of the Red Sea, such as the Erta Ale, with a crestal permanent lava lake. These ranges represent an incipient oceanic accretionary plate boundary separating Africa from Arabia. At the northern tip of Afar, the plate boundary is displaced to the axial zone of the southern Red Sea, an elongated basin oriented ~N30°W. Its southern part is characterized by an axial rift valley floored by oceanic basalt and accompanied by parallel Vine-Matthews magnetic anomalies, suggesting initial oceanic crust accretion at ~5 Ma, although alternative interpretations suggest that the entire width of the southern Red Sea is underlain by oceanic crust. Moving still farther north, the axial valley becomes discontinuous and the initial accretion of oceanic crust appears to take place in discrete cells that become younger northward. Propagation from these initial nuclei will result in a continuous axial zone of oceanic accretion. Some of these axial “deeps” are the locus of intense hydrothermal activity and metallogenesis. Moving north, the oceanic rift impacts against the Zabargad fracture zone, a major topographic-structural feature that crosses the Red Sea in a NNE direction, offsetting its axis by nearly 100 km. Zabargad island, located at the SSW end of the fracture zone, exposes a sliver of sub-Red Sea lithosphere, including mantle peridotite bodies, Pan-African granitic gneisses criss-crossed by basaltic dykes, gabbro intrusions, and a sedimentary sequence starting with pre-rift Cretaceous deposits. North of the Zabargad Fracture zone, the Red Sea lacks an axial rift valley; it probably consists of extended thinned and faulted continental crust injected by gabbros and basaltic dykes. The activation of the NNE-trending Aqaba-Dead Sea fault at about 14 Ma has deactivated rifting in the Gulf of Suez. Basalt chemistry suggests that the degree of melting of the Red Sea subaxial mantle decreases from south to north, in parallel with a decreasing spreading rate and a lesser influence of the Afar plume.
2014
- Chemical and isotopic heterogeneity in meter-scale pyroxenite-peridotite mantle sequences from Northern Apennine ophiolites (Italy)
[Abstract in Atti di Convegno]
Borghini, G; Rampone, E; Zanetti, A; Class, C; Cipriani, Anna; Hofmann, A. W.; Goldstein, S. L.; Godard, M.
abstract
Pyroxenites embedded in peridotite are often invoked as a major cause of short-length scale isotopic heterogeneities in the upper mantle, but there has been little direct evidence. We report spatially controlled chemical and Sr-Nd isotopic compositions of pyroxenites and their host peridotites from an ophiolitic mantle sequence in the Northern Apennines, Italy, with depleted mantle compositions, representing a surface exposure of veined upper mantle, a potential source for mid-oceanic-ridge basalts (MORB). Interaction between pyroxenites and adjacent mantle rocks results in centimeter-scale chemical modifications in the host peridotites, systematically lowering their Sm/Nd ratios. Over time, this interaction causes the host peridotite at >0.1 m scale to acquire an isotopic heterogeneity larger than the range defined by the peridotite and pyroxenite end-members. Moreover, the Nd-143/Nd-144 variation of a single outcrop covers most of the global Nd isotopic variability documented in abyssal peridotites. Such pyroxenite-peridotite veined mantle domains may represent the enriched component rarely found in abyssal peridotites, but often invoked to account for the low end of Nd-143/Nd-144 variations in MORB.
2014
- Melting of Plume Residue beneath the Afar: Implications for Axial Basalts Geochemistry
[Abstract in Rivista]
Barbieri, Emiliano; Brunelli, Daniele; Cipriani, Anna; Mazzucchelli, Maurizio
abstract
The Afar is the place to investigate both the evolution of the lithosphere from continental break up to incipient seafloor spreading and the interaction between rifting processes and a mantle plume. The plume has been evoked as one of the main factors involved in the development of the Afar, but its persistence beneath the depression is still a matter of debate. Recent studies have shown the lack of a well developed plume structure beneath the Afar (Hammond et al., 2013), thus suggesting its partial exhaustion. Geophysical investigations hint at an uppermost mantle dominated by broad asthenospheric upwelling (Rychert et al., 2012; Hammond et al., 2013) affected by decompression melting, feeding the magma chambers stored within both the crust and mantle, and the Afar plume magmatism. However, modern basalts erupted along the northern Afar show a strong enrichment in incompatible and trace elements that partially disagree with a shallow depleted mantle reservoir. Recent geochemical analyses indicate that part of the mantle melting process, still occurs at greater depths (> 80 km) (Ferguson et al., 2013) and several authors suggest the presence of focused diapiric upwelling (Hammond et al., 2013), which probably enhances the melting at greater depths. EMPA and LA-ICP-MS were used to investigate the composition of modern lavas sampled from the Erta Ale Chain and the Asal region in 2011 and 2013. The plume markers are recognizable but with less intensity compared to the Oligocene High Ti lavas, according to the lower activity of the Afar hot spot. Our results suggest a hybrid source characterized by two main reservoirs: an enriched mantle melting in the grt field and a shallow depleted mantle. We elaborated a numerical model that predicts the composition of the axial basalts through the mixing of melts obtained by melting of these theoretical reservoirs. We propose for the Afar region the presence of isolated volumes of enriched material genetically related to the remains of the plume. These bodies generate enriched melts that pollute the liquids obtained by the surrounding asthenosphere before they reach the surface. Isotopic investigations are in progress and will help to better define the involvement of each reservoir.
Ferguson D.J., Maclennan J., Bastow I.D., Pyle D.M., Jones S.M., Keir D., Blundy J.D., Plank T. & Yirgu G. 2013. Melting during Late-Stage Rifting in Afar Is Hot and Deep. Nature 499 (7456) (July 4), 70–3.
Rychert C.A., Hammond J.O.S., Harmon N., Kendall J.M., Keir D., Ebinger C.J., Bastow I. D., Ayele A., Belachew M., & Stuart G. 2012. Volcanism in the Afar Rift Sustained by Decompression Melting with Minimal Plume Influence. Nature Geoscience 5 (6), 406–409.
Hammond J.O.S., Kendall J.M., Stuart G.W., Ebinger C.J., Bastow I.D., Keir D., Ayele A., Belachew M., Goitom B., Ogubazghi G. & Wright T.J. 2013. Mantle Upwelling and Initiation of Rift Segmentation beneath the Afar Depression. Geology 41(6), 635–638.
2014
- Occurrence of Phlogopite in the Finero Mafic Layered Complex
[Articolo su rivista]
Giovanardi, Tommaso; Mazzucchelli, Maurizio; A., Zanetti; A., Langone; M., Tiepolo; Cipriani, Anna
abstract
Phlogopite-bearing lithologies are the main constituent of the Phlogopite-Peridotite unit of the Finero sequence and the result of pervasive migration of metasomatizing melts/fluids. Conversely, the presence of phlogopite within the associated Finero Mafic Complex, a mafic-ultramafic pluton intruded into the metamorphic basement of the Adria plate, is mentioned in literature as rare. Recent detailed fieldwork has evidenced the presence of two distinct phlogopite-rich ultramafic lithologies within the Amphibole-Peridotite unit of the Finero Mafic Complex, where phlogopite is always associated with amphibole. Field and petrographic features of these occurrences, as well as major- and trace-element mineral chemistry, are here presented to i) place constraints on the nature of the parent melt from which they have been generated and ii) to address their relationship with the other lithologies of the Finero Complex. We find that these rocks were formed by late melt migrations along shear zones under high-T conditions. The geochemical affinity of these lithologies is different to the tholeiitic-transitional affinity reported in literature for the Finero Mafic Complex. The enrichment in LREE, Th, U and Sr of the associated amphibole possibly suggests that these phlogopite-bearing lithologies are genetically related to the metasomatic events that have affected the Finero mantle massif.
2014
- Stratigraphy and facies analisys of the Langhian Dağpazarı reef complex (Mut Basin, Southern Turkey)
[Abstract in Atti di Convegno]
Vescogni, Alessandro; Bosellini, Francesca; Cipriani, Anna; Gürler, Gonca; Ilgar, Ayhan; Paganelli, Emanuele; Chiossi, Irene .
abstract
During the Early/Middle Miocene, the eastern part of the Mediterranean region registered the narrowing, and the ultimate interruption of the connections with the Indian Ocean. This event represented one of the most important episodes in the Cenozoic evolution of the Mediterranean marine biota. For this reason, the study of Middle Miocene reefal communities from this area can offer an important contribution for the reconstruction of the palaeogeography and palaeoecological settings of the Mediterranean shallow-water, carbonate-producers. The primary aim of the present study is to provide a small-scale, detailed reconstruction of the stratigraphy and facies associations of a Langhian reef complex from the Mut Formation (Mut Basin, Southern Turkey). This study has been based on field observation and microfacies analysis, with a particular emphasis on the characterization of calcareous algae associations (both corallines and green codiacean) and coral fauna. The Dağpazarı reef represents a portion of a small, isolated carbonate platform located 12 Km north from the town of Mut. Its early Langhian age has been determined by 87Sr/86Sr isotope analyses performed on several well preserved oyster samples. Dağpazarı reef is represented by two main stratigraphic sequences separated by a major erosion surface. Only a few meters of lowermost sequences are exposed, while the upper one measures about 72 meters in thickness and is characterized by the superimposition of four different cycles. During the first cycle, the amplitude of the sea transgression allowed the growth of a massive coral framestone on the shelf-edge, associated to well developed slope deposits toward the basin. In particular, concentrations of small rhodoliths with large nuclei and laminar/columnar structure characterize the shallower part of the slope, while in the middle slope the presence of Halimeda bioherms indicates a palaeodepth of about 30/50 meters. The two subsequent cycles show the superimposition, on the shelf-edge, of two similar shallowing-upward sequences, each of them related to a small-scale, transgressive phase. In particular, each sequence exhibits at the base a coralline red algae bindstone, typical of low hydrodynamic conditions, made of thin, laminar/foliose crusts associated to discoidal/irregular rhodoliths. This facies is followed by Halimeda bioherms and biocalcarenite deposits, the latters characterized by the presence of abundant “hooked” and foliose coralline algae crusts associated to gastropods concentrations. The coexistence of the latter features within biocalcarenite deposits is considered a reliable marker of the presence of seagrass beds. Both sequences terminate with the occurrence of shallow-water, massive coral framestone on the top. The fourth Dağpazarı reef cycle developed on the shelf-edge and started with a coralline red algae bindstone, but in this case, corallines colonizations were followed by a fine-grained, mud-supported biocalcarenite whose stratification dips landward. The top of the succession is characterized by coarser biocalcarenite deposits containing small, coral patches. Due to its stratigraphic setting and composition, this last sequence has been interpreted as a back-reef facies association, related to the progradation of a reef framework (now eroded) as a consequence of a final highstand phase of the sea-level. This work provides new information on some important shallow-water carbonate producers, for example Dağpazarı Halimeda bioherms represent so far the oldest recorded examples of this kind of structures; at the same time it offers a detailed frame for further, specific studies on Middle Miocene reef-building associations.
2014
- The Dağpazarı carbonate platform (Mut Basin, Southern Turkey): facies and environmental reconstruction of a coral reef system during the Middle Miocene Climatic Optimum.
[Articolo su rivista]
Vescogni, Alessandro; Bosellini, Francesca; Cipriani, Anna; G., Gurler; A., Ilgar; E., Paganelli
abstract
Plate tectonics and climate change have deeply influenced the evolution of coral reef systems of the Mediterranean during the Miocene. Most of this information is based on studies of coral reefs from the western and central sectors of th eMediterranean. This study reports facies analyses, Sr isotope stratigraphy and environmental reconstructions of the Dagpazarı coral reef system, located within the Mut Basin in Southern Turkey. Stratigraphic correlations and Sr isotope ratios on several oyster shells date the Dağpazarı reef to the early Langhian. Ten different facies have been recognized and their arrangement has led to the identification of two main depositional units. Interpretation of the biotic associations indicates that the Dağpazarı depositional system developed constantly within the euphotic zone. The reef framework was mainly built by massive faviid and poritid zooxanthellate corals, whereas loose-grain sediments were essentially produced by Halimeda, coralline red algae, or influenced by the presence of seagrass colonizations. This study highlights for the first time the great importance of Halimeda as sediment producer in the eastern Mediterranean coral reef systems. This role is related to the common occurrence of Halimeda plates within almost all the reef facies, but especially to the presence of large in situ bioherms dominated by the algal
segments. Dağpazarı Langhian Halimeda bioherms also represent the oldest of these structures so far recorded in the fossil record. The development of the Dağpazarı platform was mainly controlled by eustatic
fluctuations of the sea-level and by the morphology of the antecedent substrate. In particular, the occurrence of a pre-existent
topographic high promoted the constant presence of shallow-water environments throughout the depositional history of the reef system, with the production of euphotic carbonates both landward and basinward and the consequent formation of a small, elliptical platform. 87Sr/86Sr ages place the Dağpazarı reef system exactly within the Middle Miocene Climatic Optimum phase, the most recent warm phase of the Earth. This suggests that zooxanthellate corals were able to exert their reef-building capacity in shallow-water settings even during periods of global warming, thus being not exclusively an adaptation to cooling climates as proposed in the recent debates.
2013
- Ancient and modern oceanic islands: a classification
[Abstract in Atti di Convegno]
Palmiotto, C.; Corda, L.; Cipriani, Anna; Dick, H. J. B.; Douville, E.; Gasperini, L.; Ligi, M.; Montagna, P.; Thil, F.; Bonatti, E.
abstract
Most oceanic islands are due to excess volcanism caused by thermal and/or compositional mantle melting anomalies. We call attention here to another class of oceanic islands, due not to volcanism but to vertical motions of blocks of oceanic lithosphere related to transform tectonics. Sunken tectonic islands capped by carbonate platforms have been previously identified along the Vema and Romanche transforms in the equatorial Atlantic. We reprocessed seismic reflection lines, did new facies analyses and 87Sr/86Sr dating of carbonate samples from the carbonate platforms. A 50 km long narrow paleoisland flanking the Vema transform, underwent subsidence, erosion, and truncation at sea level; it was then capped by a 500 m thick carbonate platform dated by 87Sr/86Sr at ∼11–10 Ma. Three former islands on the crest of the Romanche transverse ridge are now at ∼900 m bsl; they show horizontal truncated surfaces of oceanic crust capped by ∼300 m thick carbonate platforms, with 10–6 Ma Sr isotopic ages. These sunken islands formed due to vertical tectonics related to transtension/transpression along long-offset slow-slip transforms. Another tectonic sunken island is Atlantis Bank, an uplifted gabbroic block along the Atlantis II transform (SW Indian Ridge) ∼700 m bsl. A modern tectonic island is St. Peter and St. Paul Rocks, a rising slab of upper mantle located at the St. Paul transform (equatorial Atlantic). “Cold” tectonic islands contrast with “hot” volcanic islands related to mantle thermal and/or compositional anomalies along accretionary boundaries and within oceanic plates, or to supra-subduction mantle melting that gives rise to islands arcs.
2013
- Downgrading Recent Estimates of Land Available for Biofuel Production
[Articolo su rivista]
Steffen, Fritz; Linda, See; Marijn van der, Velde; Rachel A., Nalepa; Christoph, Perger; Christian, Schill; Ian, Mccallum; Dmitry, Schepaschenko; Florian, Kraxner; Ximing, Cai; Xiao, Zhang; Simone, Ortner; Rubul, Hazarika; Cipriani, Anna; Carlos Di, Bella; Ahmed H., Rabia; Alfredo, Garcia; Mar’Yana, Vakolyuk; Kuleswar, Singha; Maria E., Beget; Stefan, Erasmi; Franziska, Albrecht; Brian, Shaw; Michael, Obersteiner
abstract
Recent estimates of additional land available for bioenergy production range from 320 to 1411 million ha. These estimates were generated from four scenarios regarding the types of land suitable for bioenergy production using coarse-resolution inputs of soil productivity, slope, climate, and land cover. In this paper, these maps of land availability were assessed using high-resolution satellite imagery. Samples from these maps were selected and crowdsourcing of Google Earth images was used to determine the type of land cover and the degree of human impact. Based on this sample, a set of rules was formulated to downward adjust the original estimates for each of the four scenarios that were previously used to generate the maps of land availability for bioenergy production. The adjusted land availability estimates range from 56 to 1035 ha depending upon the scenario and the ruleset used when the sample is corrected for bias. Large forest areas not intended for biofuel production purposes were present in all scenarios. However, these numbers should not be considered as definitive estimates but should be used to highlight the uncertainty in attempting to quantify land availability for biofuel production when using coarse-resolution inputs with implications for further policy development.
2013
- High-Salinity Seawater-Derived Fluids and Lower-Crust Hydrothermal Mineralization at the Vema Lithospheric Section, Central Atlantic
[Relazione in Atti di Convegno]
Alexey, Pertsev; Leonid, Aranovich; Vsevolod, Prokofiev; Nikolay, Bortnikov; Cipriani, Anna
abstract
We reconstructed a magmatic-hydrothermal transition in gabbros spatially associated with mantle peridotites from the Vema Lithospheric Section. The presence of titanian pargasite suggests the reaction of an early augite-plagioclase assemblage with a highly evolved residual melt and/or high-temperature magmatic fluid. The overprinting hydrothermal event occurs as fracture patterns with cracks filled by Cl-rich ferropargasite and olivine (Fe(0.96)Mg(1.0)4SiO(4)) locally formed by reaction between igneous orthopyroxene and magnetite. Calculations based on the olivine-forming reaction and fluid inclusions suggest cooling of the lower-crust basic bodies down to 580-610 degrees C and the ingress of fluids with salinity of 20-22% (NaCl eq.) under lithostatic pressure. The reducing nature of the fluids (logfO(2) = -19.6 to -18.8) results from relatively low-temperature (< 315 degrees C) interaction of the fluids with peridotites prior to being heated up to about 600 degrees C in the gabbro zone.
2013
- Intrusion of Oceanic-type Basaltic Melts Precedes Continental Break up
in the Red Sea Rift
[Abstract in Atti di Convegno]
Bonatti, Enrico; Ligi, Marco; Ronca, Sara; Seyler, Monique; Bosworth, William; Cipriani, Anna
abstract
The role of magmatism in continental rifting and break up and in the birth of a new ocean are not well understood.
Continental break up can take place with intense and voluminous volcanism, as in the Southern Red Sea/Afar Rift,
or in a relatively amagmatic mode, as in the Mesozoic Iberian Atlantic rift. Studies of gabbros from the Brothers
and Zabargad islands suggest that continental break up in the northern Red Sea, a relatively non-volcanic rift, is
preceded by intrusion of oceanic-type basaltic melts that crystallize at progressively shallower crustal depths as
rifting progresses towards continental break-up. A seismic reflection profile running across the central part of the
southern Thetis basin, shows a ∼5 km wide reflector ∼1.25 s below the axial neovolcanic zone. We interpret it
as marking the roof of a magma chamber or melt lens, similar to those identified below several mid-ocean ridges.
Assuming a 4.5 km/s acoustic velocity for the upper oceanic crust at Thetis, this reflector is ∼3.5 km below
the seafloor. The presence of a few kilometers deep subrift magma chamber soon after the initiation of oceanic
spreading implies the crystallization of lower oceanic crust intrusives as a last step in a sequence of basaltic melt
intrusion from pre-oceanic continental rifting to oceanic spreading. Thus, oceanic crust accretion in the Red Sea rift
starts at depth before continental break up, emplacement of oceanic basalt at the sea floor, and development of Vine-
Matthews magnetic anomalies, pointing to a rift model, where the lower continental lithosphere has been replaced
by upwelling asthenosphere before continental rupturing. This model would imply depth-dependent extension due
to decoupling between the upper and lower lithosphere with mantle-lithosphere-necking breakup before crustalnecking
breakup. This mode of initial oceanic crust accretion may have been common in Mesozoic Atlantic-type
rifts, in addition to wider, amagmatic, Iberian-type continent-ocean zones of transition.
2013
- Melting of an Hybrid Source Below the Danakil Region
[Abstract in Rivista]
Barbieri, Emiliano; Cipriani, Anna; Brunelli, Daniele; Paganelli, Emanuele
abstract
The Danakil region is a modern example of rifting located
atop a mantle plume. Along the rift system, a large number of
shield volcanoes erupted large volumes of tholeiitic magmas
with a wide compositional range, generally enriched in
incompatible and trace elements, reflecting the source
heterogeneity and the variability of melting processes that
contributed to their generation. The Danakil lavas represent
the combined product of continental rifting and ascending
mantle plume processes.
Major and trace elements were analyzed in modern lavas
sampled from the Erta Ale Chain and the Asal region and
compared to literature data. Although highly enriched in trace
elements, our lavas are significantly different when compared
to the Oligocene main lava suites generated in the earliest
stages of mantle plume activity. Based on La/Sm, Rb/Sr and
Zr/Nb ratios and REE abundances they are intermediate
between the high-Ti primitive lavas and the low-Ti tholeiitic
basalts erupted 30 Ma ago due to the arrival of the plumehead.
Trace elements abundances and geochemical modelling
indicate that our lavas derive from a “hybrid” source
characterized by a great complexity, possibly a metasomatized
sublitospheric-mantle component that includes hydrous phases
and melting at depths lower than those that generated the
Oligocene lavas.
The wide compositional range of the Afar lavas suggests
that those modern lavas erupted along the rift are not simply
the product of melting of a deep mantle plume but derive from
a composite source resulting from the interaction between the
plume tail and the surrounding sublithospheric mantle
previously metasomatized by the plume activity. As a
consequence, this very complex and heterogeneous source
undergoes extremely variable melting processes as testified
by the characteristic chemistry of each volcanic complex.
Further geochemical and isotopic investigations will help
to better constrain the signature and contribution of each of the
reservoirs and to what extent the mantle is metasomatized by
hydrous phases below the Afar region.
2013
- Meter-Scale Chemical Interaction between Pyroxenite-Derived Melts and Mantle Peridotites in the Northern Apennine Ophiolites (Italy)
[Abstract in Rivista]
Borghini, G; Rampone, E; Zanetti, A; Class, C; Cipriani, Anna; Hofmann, A; Goldstein, S; Godard, M.
abstract
Mantle peridotites from the Northern Apennine ophiolites
are characterized by the occurrence of cm-thick pyroxenite
layers originated by rather deep segregation of MORB-type
melts. Our recent work documents that during the pyroxenite
emplacement portions of the country peridotite have been
significantly modified in their modal, chemical and isotopic
compositions by reaction with melts percolating from
pyroxenite veins [1]. Here we report the results of detailed
bulk and mineral major and trace element profiles carried out
through pyroxenite-peridotite boundaries to investigate the
physico-chemical parameters governing the melt-rock reaction
process. Relative to the peridotites far (> 2 m) from the
pyroxenite veins, wall-rock peridotites show i) modal
orthopyroxene enrichment at the expense of olivine, ii) higher
Al, Ca, Si contents and slightly lower Mg# iii) Al-richer spinel
and lower-Mg# pyroxenes. Moreover, clinopyroxenes in the
wall-rock peridotites have LREE-depleted patterns and initial
%Nd(430 Ma) = +4.7-+7.6, pointing to a reaction with an
enriched tholeiitic silica-saturated melt. Along the pyroxenite peridotite
traverses, clinopyroxenes record a trace element
gradient: at the pyroxenite-peridotite contact they have the
lowest MREE-HREE abundances, with lower Sm/Nd ratios
than the distal pyroxenite-free peridotites. The overall REE
abundances progressively increase away from the pyroxenite peridotite
boundary up to about 20 cm as a result of
percolative reactive flow at decreasing melt mass. Beyond 20
cm from the contact, the HREE content decreases with
distance from the pyroxenite, while the LREEs remain at
nearly constant level, pointing to a more efficient chemical
buffering of the host peridotite on the HREE composition of
the percolating melt through ion exchange chromatographic type
processes.
2013
- Meter-scale Nd isotopic heterogeneity in pyroxenite-bearing Ligurian peridotites encompasses global-scale upper mantle variability
[Articolo su rivista]
G., Borghini; E., Rampone; A., Zanetti; C., Class; Cipriani, Anna; A. W., Hofmann; S. L., Goldstein
abstract
Pyroxenites embedded in peridotite are often invoked as a major cause of short-length
scale isotopic heterogeneities in the upper mantle, but there has been little direct evidence.
We report spatially controlled chemical and Sr-Nd isotopic compositions of pyroxenites and
their host peridotites from an ophiolitic mantle sequence in the Northern Apennines, Italy,
with depleted mantle compositions, representing a surface exposure of veined upper mantle, a
potential source for mid-oceanic-ridge basalts (MORB). Interaction between pyroxenites and
adjacent mantle rocks results in centimeter-scale chemical modifi cations in the host peridotites,
systematically lowering their Sm/Nd ratios. Over time, this interaction causes the host
peridotite at >0.1 m scale to acquire an isotopic heterogeneity larger than the range defi ned
by the peridotite and pyroxenite end-members. Moreover, the 143Nd/144Nd variation of a single
outcrop covers most of the global Nd isotopic variability documented in abyssal peridotites.
Such pyroxenite-peridotite veined mantle domains may represent the enriched component
rarely found in abyssal peridotites, but often invoked to account for the low end of 143Nd/144Nd
variations in MORB.
2013
- Nonvolcanic tectonic islands in ancient and modern oceans
[Articolo su rivista]
Palmiotto, Camilla; Corda, Laura; Ligi, Marco; Cipriani, Anna; Dick, Henry J. B.; Douville, Eric; Gasperini, Luca; Montagna, Paolo; Thil, François; Borsetti, Anna Maria; Balestra, Barbara; Bonatti, Enrico
abstract
Most oceanic islands are due to excess volcanism caused by thermal and/or compositional mantle
melting anomalies. We call attention here to another class of oceanic islands, due not to volcanism but to
vertical motions of blocks of oceanic lithosphere related to transform tectonics. Sunken tectonic islands
capped by carbonate platforms have been previously identified along the Vema and Romanche transforms
in the equatorial Atlantic. We reprocessed seismic reflection lines, did new facies analyses and 87Sr/86Sr
dating of carbonate samples from the carbonate platforms. A 50 km long narrow paleoisland flanking the
Vema transform, underwent subsidence, erosion, and truncation at sea level; it was then capped by a 500
m thick carbonate platform dated by 87Sr/86Sr at 11–10 Ma. Three former islands on the crest of the
Romanche transverse ridge are now at 900 m bsl; they show horizontal truncated surfaces of oceanic
crust capped by 300 m thick carbonate platforms, with 10–6 Ma Sr isotopic ages. These sunken islands
formed due to vertical tectonics related to transtension/transpression along long-offset slow-slip
transforms. Another tectonic sunken island is Atlantis Bank, an uplifted gabbroic block along the Atlantis
II transform (SW Indian Ridge) 700 m bsl. A modern tectonic island is St. Peter and St. Paul Rocks, a
rising slab of upper mantle located at the St. Paul transform (equatorial Atlantic). ‘‘Cold’’ tectonic islands
contrast with ‘‘hot’’ volcanic islands related to mantle thermal and/or compositional anomalies along
accretionary boundaries and within oceanic plates, or to supra-subduction mantle melting that gives rise
to islands arcs.
2013
- Serpentinization of mantle peridotites along an uplifted lithospheric section, Mid Atlantic Ridge at 11° N
[Articolo su rivista]
Chiara, Boschi; Enrico, Bonatti; Marco, Ligi; Brunelli, Daniele; Cipriani, Anna; Luigi, Dallai; Massimo, D'Orazio; Gretchen L., Früh Green; Sonia, Tonarini; Jaime D., Barnes; Rosa M., Bedini
abstract
Abstract Mantle peridotites from an exposed lithospheric section (Vema Lithospheric Section, VLS), generated during ~ 26 Ma at a ~ 80 km long Mid Atlantic Ridge segment (11° N), have been sampled and studied to understand the evolution of the serpentinization process. The VLS was uplifted due to a 10 Ma transtensional event along the Vema transform. Before the uplift residual mantle rocks were lying beneath a 0.8–1.3 km thick basaltic crustal layer. The major and trace element compositions of the serpentinites, as well as their H, O, Sr, Cl and B isotopic compositions were interpreted based on thermal models of lithospheric spreading from ridge axis. The results suggest that serpentinization occurred mostly near the ridge axis. Serpentinization temperatures, estimated from stable isotopes, are consistent with resetting of the closure temperatures during the tectonic uplift of the lithospheric sliver, reflected by decreasing δ18O and increasing δ11B values. Modeling shows that the thermal influence of the transtensional event affected mainly the region close to the RTI (ridge–transform intersection). Petrological, elemental and isotopic data suggest that, when the ultramafic basal unit of the VLS was uplifted and exposed on the ocean floor, serpentinization became superseded by low temperature water–rock reactions, with Fe–Mn crust formation, which is still progressing, as recorded by δD. Ultramafic mylonites, prevalent in a short stretch of the VLS, show only a partial serpentinization process, together with pervasive contamination by low-temperature Fe–Mn crust.
2012
- Birth of an ocean in the Red Sea: Initial pangs
[Articolo su rivista]
Marco, Ligi; Enrico, Bonatti; Giovanni, Bortoluzzi; Cipriani, Anna; Luca, Cocchi; Fabio Caratori, Tontini; Eugenio, Carminati; Luisa, Ottolini; Antonio, Schettino
abstract
We obtained areal variations of crustal thickness, magnetic intensity, and degree of melting of the sub-axial upwelling mantle at Thetis and Nereus Deeps, the two northernmost axial segments of initial oceanic crustal accretion in the Red Sea, where Arabia is separating from Africa. The initial emplacement of oceanic crust occurred at South Thetis and Central Nereus roughly ∼2.2 and ∼2 Ma, respectively, and is taking place today in the northern Thetis and southern Nereus tips. Basaltic glasses major and trace element composition suggests a rift-to-drift transition marked by magmatic activity with typical MORB signature, with no contamination by continental lithosphere, but with slight differences in mantle source composition and/or potential temperature between Thetis and Nereus. Eruption rate, spreading rate, magnetic intensity, crustal thickness and degree of mantle melting were highest at both Thetis and Nereus in the very initial phases of oceanic crust accretion, immediately after continental breakup, probably due to fast mantle upwelling enhanced by an initially strong horizontal thermal gradient. This is consistent with a rift model where the lower continental lithosphere has been replaced by upwelling asthenosphere before continental rupturing, implying depth-dependent extension due to decoupling between the upper and lower lithosphere with mantle-lithosphere-necking breakup before crustal-necking breakup. Independent along-axis centers of upwelling form at the rifting stage just before oceanic crust accretion, with buoyancy-driven convection within a hot, low viscosity asthenosphere. Each initial axial cell taps a different asthenospheric source and serves as nucleus for axial propagation of oceanic accretion, resulting in linear segments of spreading.
2012
- Reducing reactions of hydrothermal front in lower-crustal magmatically active zone: an example from the Vema lithospheric section, central Atlantic
[Abstract in Atti di Convegno]
Pertsev, A.; Cipriani, Anna; Aranovich, L.; Prokofiev, V.
abstract
In this work we have attempted to reconstruct hornblende-forming mineral reactions in
oceanic lower-crust gabbro to trace the magmatic/hydrothermal transition and to constrain
temperature, pressure, oxygen fugacity, and fluid composition for the reaction zone. The
results are based on mineral chemistry including trace elements, study of fluid inclusions and
thermodynamic calculations.
2011
- Deep versus shallow melt stagnation in an ultra-slow / ultra-cold ridge segment: the Andrew Bain southern RTI (SWIR)
[Poster]
Paganelli, Emanuele; Brunelli, Daniele; Seyler, M.; Bonatti, E.; Cipriani, Anna; Ligi, M.
abstract
The Andrew Bain Fracture Zone (ABFZ) represents one of the largest transform faults in the ridge system spanning 750 km in length with a characteristic lens-shape structure. The southern Ridge-Transform Intersection represents the deepest sector of the whole South West Indian Ridge system. During the Italian-Russian expedition S23-AB06, the seafloor in the Southern Ridge Transform Intersection (RTI) has been sampled recovering only ultramafic material in the majority of the dredging sites. The sampled spinel and plagioclase peridotites show hybrid textures, characterized either by deep spinel-field impregnation assemblages (sp+cpx±opx±ol) or by plagioclase-field equilibrated patches and mineral trails (pl+cpx±ol) marked by both crystallization of newly formed plagioclase-field equilibrated trails and formation of plagioclase coronas around spinel. The ones collected from ridge axis show also late gabbroic pockets and veins, variably enriched in clinopyroxene. Overall textures account for important melt percolation/stagnation events occurred in the plagioclase and spinel field. Major and trace element distribution in pyroxenes and spinels from spinel-bearing peridotites overall follow a general melting trend accompanied by a progressive re-equilibration to lower P/T facies at all scales. However, only few samples can be linked to near fractional melting, while the majority of them shows REE pattern and trace element concentrations that cannot be reproduced by fractional melting process. Open-system melting (OSM) better reproduces measured REE patterns. Modeling melting in an open system scenario requires high residual porosity to be accounted for along with generally enriched melts to influx the melting parcel at depth. Melting at high residual porosity suggests a near-batch regime in which enriched melts stagnate in the spinel field. Inhibition of melt segregation during melt/rock interaction asks for a permeability barrier to develop in the region where the mantle potential temperature is suggested to still be high enough to allow partial melting. Energy consumption during garnet breakdown and porosity decrease due to reaction with silica-saturated melt could play a key role in the formation of short scale permeability barriers beneath ABFZ. Alternatively an anomalously thick conductive layer can be responsible of deep inhibition of melting and melt accumulation at depth.
2011
- Foramol facies in equatorial carbonates: insight from Miocene Atlantic platforms
[Abstract in Atti di Convegno]
Bonatti, E.; Cipriani, Anna; Corda, Laura; Montagna, Paolo; Palmiotto, Camilla
abstract
Foramol facies in equatorial carbonates: insight from Miocene Atlantic platforms
2011
- Initial burst of oceanic crust accretion in the Red Sea due to edge-driven mantle convection
[Articolo su rivista]
M., Ligi; E., Bonatti; F. C., Tontini; Cipriani, Anna; L., Cocchi; A., Schettino; G., Bortoluzzi; V., Ferrante; S., Khalil; N. C., Mitchell; N., Rasul
abstract
The 500 m.y. cycle whereby continents assemble in a single supercontinent and then fragment and disperse again involves the rupturing of a continent and the birth of a new ocean, with the formation of passive plate margins. This process is well displayed today in the Red Sea, where Arabia is separating from Africa. We carried out geophysical surveys and bottom rock sampling in the two Red Sea northernmost axial segments of initial oceanic crust accretion, Thetis and Nereus. Areal variations of crustal thickness, magnetic intensity, and degree of melting of the subaxial upwelling mantle reveal an initial burst of active oceanic crust generation and rapid seafl oor spreading below each cell, occurring as soon as the lid of continental lithosphere breaks. This initial pulse may be caused by edge-driven subrift mantle convection, triggered by a strong horizontal thermal gradient between the cold continental lithosphere and the hot ascending asthenosphere. The thermal gradient weakens as the oceanic rift widens; therefore the initial active pulse fades into steady, more passive crustal accretion, with slower spreading and along axis rift propagation.
2011
- Nonchondritic 142Nd in suboceanic mantle peridotites
[Articolo su rivista]
Cipriani, Anna; Enrico, Bonatti; Richard W., Carlson
abstract
The discovery that several solid Earth reservoirs have a superchondritic 142Nd/144Nd ratio led to the hypothesis that either the bulk silicate Earth is not chondritic or that a subchondritic reservoir lies hidden somewhere within the Earth’s interior. One important reservoir, i.e., mid‐ocean ridge peridotites representing the main component of the upper oceanic mantle and the source of mid‐ocean ridge basalt, has never been tested for 142Nd/144Nd. We determined the 142Nd/144Nd ratio in clinopyroxene separated from two peridotites and a pyroxenite from the SW Indian Ridge and one peridotite from the northern Mid‐Atlantic Ridge. All samples analyzed have superchondritic 142Nd/144Nd ratios in line with mantle‐derived material measured to date, except for some ancient cratonic rocks.
2011
- Pyroxenites in peridotites from External Liguride ophiolites (Italy): Insights on small scale heterogeneities in MORB mantle
[Abstract in Rivista]
Borghini, G; Rampone, E; Zanetti, A; Class, C; Cipriani, Anna; Hofmann, A. W.; Goldstein, S. L.
abstract
The occurrence of mafic layers in peridotites constitutes
an important compositional heterogeneity in the mantle, and
their role in mantle melting and basalt generation is currently
debated. We present field, chemical and isotopic data on
pyroxenites and host peridotites from the western peridotite
massifs of the External Liguride ophiolitic Units (Northern
Apennines, Italy). Pyroxenites (mostly spinel-websterites)
occur as cm-thick bands (up to 12 cm) parallel to the tectonite
mantle foliation, and ,together with the peridotites, they are
partially recrystallized at plagioclase-facies conditions.
Whole-rock and mineral compositions are extremely
heterogeneous, covering almost the entire compositional range
of worldwide lithospheric pyroxenites (Mg# = 74-88, Al2O3 =
10-17 wt%, CaO = 7-20 wt%). The pyroxenite chemistry
reflects high-pressure magma segregation of tholeiitic melts
dominated by clinopyroxene crystallization. A multi-step,
sequential leaching procedure on clinopyroxene separates
enables us to remove partial contamination and provides
reliable Sr isotope data. The Sr and Nd compositions of
clinopyroxenes from pyroxenites and peridotites fall in the
typical range of normal MORB (87Sr/86Sr =0.7023-0.7029;
143Nd/144Nd =0.5134-0.5128). Internal Sm-Nd isochrons on
plagioclase-clinopyroxene pairs from two pyroxenites yield
ages of 183±14 Ma and 177±12 Ma for the low-P mantle
exhumation. On a slightly larger spatial scale, chemical and
isotopic profiles through the pyroxenite-peridotite boundaries
indicate cm-scale modification of the wall-rock peridotite,
presumably related to emplacement of the pyroxenites. This
suggests that deep melt intrusion can locally modify the host
peridotites and introduce small scale compositional
heterogeneity in a MORB mantle.
2011
- REE pattern rotation in an open system melting: case studies from slow and ultraslow spreading ridges
[Abstract in Rivista]
Cipriani, Anna; Brunelli, Daniele; Seyler, Monique; Paganelli, Emanuele; Barbieri, Emiliano
abstract
The REE compositional space provides a reliable means to recognize the degree of depletion and melt rock reactional events undergone by a parcel of mantle. We model residual clinopyroxene compositions from slow (MAR) and ultraslow (SWIR) sectors of the Mid Ocean Ridges. REE ratios (e.g. SmN/YbN vs. YbN) show compositional trends crosscutting the expected partial melting trends at the typical kilometer length scale. In the REE compositional space they appear as pattern rotations around a mid-point. Open-system melting modeling reveals the intensity of the rotation and the position of the pivot element, depending mainly on the ratio between input/output melt flux and on the enrichment of the percolating melt with respect to the depleted screen. Variations of the residual porosity of the system (Ø) with respect to the degree of melting F result in variations of the nature of the melting process. At low Ø/F the process behaves as near-fractional while at high Ø/F the process behaves as near batch. In an open melting system scenario the effect of an enriched melt fluxing a melting portion can be strongly enhanced by melt stagnation i.e. approaching a near-batch process with low melt output. Model trends present strong enrichment of SmN/YbN at decreasing YbN values. At high Ø/F even YbN increases along with SmN/YbN. These trends well fit measured countertrends at the km lengthscale, i.e. a typical dredge lengthscale. Our observations suggest that in some portions of the melting region the vertical porosity profile can vary resulting in a variability of the nature of the melting process from near-fractional (when extraction prevails) to near batch (when stagnation prevails). Percolation of enriched melts through a melting mantle parcel results in REE pattern rotation whose intensity and midpoint depends on Ø/F, mixing factors and obviously on the composition of the melt itself. Our preliminary results suggest that, first, melt batches generated deep in the mantle are transported out of equilibrium to shallower portions of the melting region and redistributed to the rock porosity. Second, that porosity barriers are present at depth resulting in melt accumulation and stagnation in the spinel facies of the melting region.
2011
- Small scale heterogeneities in MORB mantle: Insights on pyroxenite-peridotite association from External Liguride ophiolites (Italy)
[Abstract in Rivista]
Borghini, G; Rampone, Zanetti; Cipriani, Anna; E, ; Aw, A. W.; Class, C; Hofmann, ; Goldstein, S. L.
abstract
The occurrence of mafic layers in peridotites constitutes an important
compositional heterogeneity in the mantle, and their role in mantle
melting and basalt generation is currently debated (e.g. Hirschmann &Stolper, 1996; Salters & Dick, 2002). Pyroxene-rich lithologies are
commonly documented in subcontinental lithospheric mantle, from both
tectonically-emplaced ultramafic massifs and mantle xenoliths (e.g.
Downes, 2007), and rarely sampled in abyssal peridotites (e.g. Warren et
al., 2009). They are mostly interpreted as high-pressure magmatic
products and rarely as remnants of recycled oceanic crust. However, the
origin and composition of such lithologies, and their potential role in
creating small-scale heterogeneities in the MORB mantle remain still
poorly constrained. In this study, we present field, chemical and isotopic
data on pyroxenites and host peridotites from some peridotite massifs of
the External Liguride ophiolitic Units (Northern Apennines, Italy) with the
aim to widen the knowledge on the origin of pyroxenites in MORB-type
settings and discuss the occurrence and extent of chemical and isotopic
heterogeneities in the MORB mantle related to the pyroxenitic component.
At this latter purpose, pyroxenites and host peridotites have been
accurately sampled from single dm-scale profiles, in order to test whether
the existence of lithologic heterogeneities in the mantle in turn reflects the
occurrence of isotopic contrasts at the small scale. Pyroxenites occur as
cm-thick bands (up to 12 cm) parallel to the tectonite mantle foliation and
vary from spinel-bearing websterite to clinopyroxenite. As the host
peridotites, they are partially recrystallized at plagioclase-facies
conditions. The occurrence of orthopyroxene-rich rim between pyroxenite
and peridotite and large poikilitic orthopyroxene in the wall-rock
peridotites indicate that host peridotites have interacted with melts related
to pyroxenite intrusion. These latters display very heterogeneous
whole-rock chemistry, almost covering the entire compositional range
defined by worldwide lithospheric pyroxenites (XMg = 74-88, Al2O3 = 10-17
wt%, CaO = 7-20 wt%). The pyroxenite chemistry reflects high-pressure
magma segregation of tholeiitic melts dominated by clinopyroxene
crystallization. Both mineral and bulk-rock compositions from
peridotite-pyroxenite traverses reveal that the host peridotites have been
significantly modified in terms of major (e.g. XMg, Al2O3, CaO) and trace
element (e.g. the LREE) composition by the interaction with pyroxenite
component. A multi-step, sequential leaching procedure on clinopyroxene
separates enables us to remove partial contamination and provides
reliable Sr isotope data. The Sr and Nd compositions of clinopyroxenes
from pyroxenites and peridotites fall in the typical range of normal MORB (
87Sr/86Sr = 0.7023-0.7029; 143Nd/144Nd = 0.5134-0.5128). Internal Sm-Nd
isochrons based on plagioclase, clinopyroxene and whole-rock from
several pyroxenite samples yield ages ranging from 174 to 183 Ma (with
errors between ±11-25) for the low-P mantle exhumation. On a slightly
larger spatial scale, isotopic profiles through the pyroxenite-peridotite
boundaries indicate cm-scale modification of the wall-rock peridotite,
presumably related to emplacement of the pyroxenites. This suggests that
deep melt intrusion can locally modify the host peridotites and introduce
small scale compositional heterogeneity in a MORB mantle.
References: Downes, H. (2007): Lithos, 99, 1-24; Hirschmann, M.M. &
Stolper, E.M. (1996): Contrib, Min. Pet., 124, 185-208; Salters, V.J.M. &
Dick. H.J.M. (2002): Nature, 418, 68-72; Warren, J., Shimizu, N.,
Sakaguchi, C., Dick, H.J.M. & Nakamura, E. (2009): J. Geophys. Res.,
114, B12203.
2011
- Upper mantle isotopic heterogeneities - global overview with new results from Alpine-Apennine ophiolites
[Abstract in Rivista]
Rampone, E; Borghini, G; Hofmann, A. W.; Class, C; Cipriani, Anna; Zanetti, A; Goldstein, S. L.
abstract
Studies on modern oceanic lithosphere and ophiolites show that the petrogenesis of the oceanic mantle is complex. Its chemistry does not reflect simple trace element depletion by partial melting, and this complexity is highlighted by chemical and isotopic heterogeneities in the mantle, and by isotopic contrasts between mantle and crust. We present an overview of the present knowledge on isotopic heterogeneities of Sr, Nd and Os in present-day oceanic peridotites and Alpine-Apennine ophiolites. Compared to modern oceanic lithosphere, these ophiolites represent a fossil analogue of ocean-continent transitions and slow spreading settings. Previous studies show that mantle peridotites record significant isotopic heterogeneity, detectable on a wide range of length scales, much larger than observed in associated MORB. This reflects two major aspects. First, the MORB mantle source region is larger than peridotite sampling scales, and MORB represent aggregated melts that smooth and average mantle source heterogeneities, as supported by melt extraction models (Stracke and Bourdon, 2009). Second, isotopic heterogeneities in oceanic peridotites may result from a combination of processes, reflecting a long-lived history: i) old depletion events, ii) pyroxenite components in the mantle source, iii) recent pre- and/or post-melting metasomatism. In this context, we focus on two major issues: 1) What is the significance of extremely depleted isotopic signature found in oceanic peridotites - do they reflect a subcontinental origin, or preserved isotopic heterogeneities in the asthenospheric MORB source, inherited from old (1-2 Ga) depletion events, not sufficiently stirred by convection; 2) What is the length scale, amplitude and distribution of isotopic heterogeneities in the oceanic mantle, and their relation to lithologic heterogeneities like pyroxenites? Specifically, the effect of a pyroxenite component in creating small-scale chemical and isotopic heterogeneities in the mantle has often been advocated but not adequately investigated. New isotope studies of pyroxenite bands (clinopyroxenites and spinel websterites) and host peridotites from the External Liguride ophiolites (Northern Apennines, Italy) show that pyroxenites define a large Nd isotope range (143Nd/144Nd =0.512936-0.513401). Chemical and isotopic profiles through the pyroxenite-peridotite boundaries indicate that the interaction of the pyroxenites with the peridotite wall rock creates Nd isotopic variations resulting in an overall Nd isotopic range in the host mantle (143Nd/144Nd=0.512799-0.513544, initial EpsilonNd=3-16) that covers nearly the entire abyssal peridotite field. This suggests that pyroxenite components can induce extreme small scale isotopic changes, and strongly calls for detailed field-based studies in spatially-controlled settings in order to unravel the size and distribution of upper mantle isotopic heterogeneity. Stracke A., and Bourdon, B. (2009). GCA 73, 218-238.
2011
- Water in Mid Ocean Ridge Basalts: Some Like it Hot, Some Like it Cold
[Monografia/Trattato scientifico]
Ligi, Marco; Bonatti, Enrico; Brunelli, Daniele; Cipriani, Anna; Ottolini, Luisa
abstract
The presence in the Earth’s mantle of even small amounts of water and other volatiles has major effects: first, it lowers drastically mantle’s viscosity, thereby facilitating convection and plate tectonics; second, it lowers the melting temperature of the rising mantle affecting the formation of the oceanic crust. H2O concentration in oceanic basalts stays below 0.2 wt% except for basalts sampled near “hot spots” that contain significantly more H2O than normal MORB, implying that their mantle plume sources are unusually H2O-rich. Basalts sampled in the Equatorial Atlantic close to the Romanche transform, a thermal minimum in the Ridge system, have a H2O content that increases as the ridge is cooled approaching the transform offset. These basalts are Na-rich, being generated by low degrees of melting of the mantle, and contain unusually high ratios of light versus heavy rare earth elements implying the presence of garnet in the melting region. H2O enrichment is due not to an unusually H2O-rich mantle source, but to a low extent of melting of the upwelling mantle, confined to a deep wet melting region. Numerical models predict that this wet melting process takes place mostly in the mantle zone of stability of garnet. This prediction is verified by the geochemistry of our basalts showing that garnet must indeed have been present in their mantle source. Thus, oceanic basalts are H2O-rich not only near “hot spots”, but also at “cold spots”.
2010
- Heterogeneous melting and refertilization of a mantle parcel in a cold spot: Andrew Bain fracure zone (SWIR)
[Poster]
Paganelli, Emanuele; Brunelli, Daniele; M., Seyler; E., Bonatti; Cipriani, Anna; M., Ligi
abstract
abstract
2010
- Nd, Sr and Pb isotopic composition of metasomatised xenoliths from the backarc Patagonian MantleWedge: Insights into the origin of the uprising melts
[Abstract in Rivista]
Zanetti, A.; Mazzucchelli, Maurizio; Hémond, C.; Cipriani, Anna; Bertotto, G. W.; Cingolani, C. A.; Vannucci, R.
abstract
Information about the geochemical composition of metasomatic melts migrating through the Patagonian mantle wedge is provided by the ultramafic xenoliths occurrence of Tres Lagos (TL; lat. 49.13°S, long. 71.18°W), Argentina.Such a locality is placed at the eastern border of the Meseta de la Muerte backarc basaltic plateau, wherea post-plateau volcanic diatreme contains mantle xenoliths in both pyroclastites and lavas. Its latitude corresponds with the Northern limit of the Austral Volcanic Arc (AVZ), which is separated from the Southern Volcanic Zone (SVZ) by a gap in the arc magmatism ranging between 49° and 46°300 latitude S. The analysed xenoliths have been distinguished into two groups (Group 1 & 2). Group 1 consists of lherzolites and harzburgites, whereas Group 2 is formed by harzburgites. The texture of the Group 1 lherzolites varies from protogranular to granoblastic to porphyroblastic, whereas Group 1 harzburgites have always granoblastic texture. Group 2 harzburgites have granular texture, which may change to porphyroblastic owing to the random concentration of large olivine and orthopyroxene crystals. The clinopyroxenes (Cpx) from Group 1 lherzolites have PM-normalised REE patterns ranging from LREEdepleted (LaN/SmN= 0.24-0.37), to LREE-enriched (LaN/YbN up to 4.08) and spoon-shaped: the latter have minimum at Pr and Pr-Yb concentrations similar to those shown by the LREE-depleted Cpx.The Cpx from Group 1 harzburgites have lower REE concentrations with respect to the lherzolite ones and their REE patterns vary from HREE-enriched, steadily fractionated, (LaN/YbN = 0.21–0.35, Ybn 1-2) to spoonshaped (LaN/SmN = 2.81; SmN/YbN = 0.89; YbN 3. The Cpx from the Group 2 harzburgites have convex-upward (LaN/SmN = 0.31; SmN/YbN = 1.50) to LREE enriched (LaN/YbN = 2.94) patterns.The Sr, Nd and Pb isotopic compositions of the Group 1 clinopyroxenes form arrays spanning from DM to thefield delimited by the TL basaltic lavas, pointing to EMI end-member. Conversely, Group 2 Cpx have much moreradiogenic Sr and less radiogenic Nd values, approaching more closely the EMI and EMII end-members: these features are associated to unradiogenic lead isotopic compositions (206Pb/204Pb = 17.4-18.1; 207Pb/204Pb = 15.55-15.60; 208Pb/204Pb = 37.3-38.5). The combination of petrographic, trace element and isotopic features indicate that TL harzburgites are likely residua after melt-assisted partial melting triggered by melt/fluid migration in the hottest, and perhaps deeper, parts of the pristine DM lithosphere. The interpretation of the Pb, Sr and Ndisotope composition of Group 2 Cpx is not trivial. In analogy with the interpretation proposed for SWIR, it could unravel the occurrence of mantle sources which incorporated ancient crust and failed to homogenise with the DM mantle. Alternatively, it could be the evidence for ancient continental crust of the South America plate dragged down into the mantle by slab motion.
2009
- 26 Million Years of Mantle Upwelling Below a Segment of the Mid Atlantic Ridge: the Vema Lithospheric Section Revisited
[Articolo su rivista]
Cipriani, Anna; E., Bonatti; Brunelli, Daniele; M., Ligi
abstract
Temporal variations of temperature and composition of the mantle upwelling below a 80-km long segment of the Mid Atlantic Ridge were reconstructed from 20 to 4 Ma ago from peridotites sampled along a > 300-km long section of oceanic lithosphere (Vema Lithospheric Section or VLS) exposed south of the Vema transform at 11° N [Bonatti, E., Ligi, M., Brunelli, D., Cipriani, A., Fabretti, P., Ferrante, V., Gasperini, L., Ottolini, L., 2003. Mantle thermal pulses below the Mid-Atlantic Ridge and temporal variation in the formation of oceanic lithosphere, Nature, 423, 499–505]. We extended this time interval from 26 to 2 Ma by sampling mantle ultramafics at 18 new sites along the VLS. Peridotite orthopyroxene, clinopyroxene and spinel chemistry suggest a weak trend of decreasing extent of melting of the mantle from 26 to 18.5 Ma ago with superimposed short-wavelength (~ 4 Ma) oscillations followed by a steady increase of degree of melting from 18.5 to 2 Ma ago, with superimposed 3–4 Ma oscillations. Temporal variations of crustal thickness inferred from the Residual Mantle Bouguer Anomaly calculated from gravity data reveal similar trends. The older (26 to 18.5 Ma) and the younger (18.5 to 2 Ma) mantle suites differ in cpx Na2O content and CaO/Al2O3 ratio, suggesting that not only the thermal regime, but also the composition of the mantle source might have been different in the two suites. The two trends are separated by a ~ 1.4 Ma-long stretch (from 18.2 to 16.8 Ma) where deformed ultramafic mylonites prevail, indicating probably an interval of nearly a-magmatic lithospheric emplacement at ridge axis, corresponding to a thermal minimum. Spatially offset correlation along the VLS of crustal thickness (i.e., quantity of basaltic melt released by the mantle) and mantle peridotite degree of melting led to an estimate of ~ 16.1 mm/a for the solid mantle average velocity of upwelling, a value close to the average half spreading rate for the 26 Ma interval covered by the VLS. However, peridotite clinopyroxene geothermometry shows oscillations superimposed on a decreasing trend of calculated equilibration temperature from 26 to 18.5 Ma ago, followed by a steady increase from 16 to 4 Ma ago, suggesting that the solid mantle upwelling velocity varied through time. These results hint at the existence of ~ 10–20 Ma cycles in the activity of the northern Mid Atlantic Ridge.
2009
- A 19 to 17 Ma amagmatic extension event at the Mid-Atlantic Ridge: ultramafic mylonites from the Vema Lithospheric Section
[Articolo su rivista]
Cipriani, Anna; E., Bonatti; M., Seyler; H., Brueckner; Brunelli, Daniele; L., Dallai; S., Hemming; M., Ligi; L., Ottolini; B., Turrin
abstract
A >300 km long lithospheric section (Vema Lithospheric Section or VLS) is exposed south of the Vematransform at 11N in the Atlantic. It is oriented along a seafloor spreading flow line and represents 26 Maof accretion at a single 80 km long segment (EMAR) of the Mid-Atlantic Ridge. The basal part of the VLSexposes a mantle unit made mostly of relatively undeformed coarse-grained/porphyroclastic peridotitesthat were sampled at close intervals. Strongly deformed mylonitic peridotites were found at 14 contiguoussites within a 80 km stretch (4.7 Ma interval); they are dominant in a time interval of 1.4 Ma, fromcrustal ages of 16.8 to 18.2 Ma (mylonitic stretch). Some of the mylonites are ‘‘dry,’’ showing anhydroushigh-T deformation, but most contain amphibole. The mylonitic peridotites tend to be less depleted thanthe porphyroclastic peridotites on the basis of mineral major and trace elements composition, suggestingthat the mylonites parent was a subridge mantle that underwent a relatively low degree of melting. The Sr,Nd, and O isotopic composition of the amphiboles is MORB-like and suggests either that seawater did notcontribute to their isotopic signature or that their isotopic ratios re-equilibrated during fluid circulation inthe upper mantle. Four 40Ar/39Ar ages, on three amphiboles separated from the peridotites, are close tocrustal ages predicted from magnetic anomalies, confirming that the amphiboles formed close to ridge axis.We propose that crustal accretion at the EMAR segment has been mostly symmetrical for the 26 Ma of itsrecorded history, except for the 1.4 Ma interval of prevalent ultramafic mylonites (mylonitic stretch) thatmay record a period of quasi-amagmatic asymmetric accretion of oceanic lithosphere close to the ridge–Vema transform intersection, possibly with development of detachment faults. This interval maycorrespond to a thermal minimum of the subridge upwelling mantle, marking the transition from a periodof decreasing to one of increasing mantle melting below the EMAR segment.
2009
- Evidence for ultra-depleted Pb isotopic component in the backarc Patagonian mantle wedge.
[Abstract in Rivista]
Rivalenti, Giorgio; Mazzucchelli, Maurizio; Zanetti, A.; Hémond, C.; Cipriani, Anna
abstract
Inferences on melt and fluid migration trough the Patagonin mantle wedge are provided by the ultramafic xenoliths occurrence of Tres Lagos (TL; lat. 49.13°S, long. 71.18°W). It is placed at the eastern border of the Meseta de la Muerte backarc basaltic plateau, where a post-plateau volcanic diatreme contains mantle xenoliths in both pyroclastites and lavas. Its latitude corresponds with the Northern limit of the Austral Volcanic Arc (AVZ), which is separated from the Southern Volcanic Zone (SVZ) by a gap in the arc magmatism between 49° and 46°30′ latitude S. The selected xenoliths have been distinguished into two groups (Group 1 & 2). Group 1 consists of lherzolites and harzburgites, whereas Group 2 is constituted only by harzburgites. The Sr, Nd and Pb isotopic compositions of the Group I clinopyroxenes (Cpx) form arrays from DM to the TL basaltic lavas, according to the presence of EM1 component. Group 2 Cpx have much more radiogenic Sr and less radiogenic Nd values, approaching those of EM1 and EM2 end-members: these features are associated to very unradiogenic lead isotopic compositions (206Pb/204Pb = 17.4-18.1; 207Pb/204Pb = 15.55-15.60; 208Pb/204Pb = 37.3-38.5). The combination of petrographic, trace element and isotopic fetures indicate that TL harzburgites are residua after melt-assisted partial melting triggered by melt/fluid migration in the hottest, and perhaps deeper, parts of the pristine DM lithosphere. The interpretation of the Pb isotope composition of Group 2 Cpx is not trivial. In analogy with the interpretation proposed for SWIR, it could unravel the occurrence of mantle sources which incorporated ancient crust and failed to homogenise with the DM mantle. Alternatively, it could be the evidence for ancient continental crust of the South America plate dragged down into the mantle by slab motion.
2009
- Evidence for ultra-depleted Pb isotopic metasomatic liquid in the backarc Patagonian Mantle Wedge
[Abstract in Rivista]
Rivalenti, Giorgio; Mazzucchelli, Maurizio; Zanetti, A; Hémond, C; Cipriani, Anna; Bertotto, Gw; Cingolani, Ca
abstract
Insights into the geochemical composition of melts and fluids migrating trough the Patagonian mantle wedge are provided by the ultramafic xenoliths occurrence of Tres Lagos (TL; lat. 49.13°S, long. 71.18°W). This locality is placed at the eastern border of the Meseta de la Muerte backarc basaltic plateau, where a post-plateau volcanic diatreme contains mantle xenoliths in both pyroclastites and lavas. Its latitude corresponds with the Northern limit of the Austral Volcanic Arc (AVZ), which is separated from the Southern Volcanic Zone (SVZ) by a gap in the arc magmatism ranging between 49° and 46°30′ latitude S. The selected xenoliths have been distinguished into two groups (Group 1 & 2). Group 1 consists of lherzolites and harzburgites, whereas Group 2 is only formed by harzburgites.The texture of the Group 1 lherzolites is protogranular to granoblastic and porphyroblastic, whereas Group 1 harzburgites have always granoblastic texture. Group 2 harzburgites have granular texture, which may fade into porphyroblastic owing to the presence of large olivine and orthopyroxene crystals.The clinopyroxenes (Cpx) from Group 1 lherzolites have PM-normalised REE patterns varying from LREE-depleted (Lan/Smn= 0.24-0.37), to LREE-enriched (Lan/Ybn up to 4.08) and spoon-shaped: the latter have minimum at Pr and Pr-Yb concentrations similar to those shown by the LREE-depleted Cpx.The Cpx from Group 1 harzburgites have lower REE concentrations with respect to the lherzolite ones and their REE patterns vary from HREE-enriched, steadily fractionated, (Lan/Ybn = 0.21–0.35, Ybn ~ 1-2) to spoon-shaped (Lan/Smn = 2.81; Smn/Ybn = 0.89; Ybn ~ 3).The Cpx from the Group 2 harzburgites have convex-upward (Lan/Smn = 0.31; Smn/Ybn = 1.50) to LREE-enriched (Lan/Ybn = 2.94) patterns.The Sr, Nd and Pb isotopic compositions of the Group 1 clinopyroxenes form an array from DM to the TL basaltic lavas, according to the presence of EM1 component. Group 2 Cpx have much more radiogenic Sr and less radiogenic Nd values, approaching those of EM1 and EM2 end-members: these features are associated to very unradiogenic lead isotopic compositions (206Pb/204Pb = 17.4-18.1; 207Pb/204Pb = 15.55-15.60; 208Pb/204Pb = 37.3-38.5). The combination of petrographic, trace element and isotopic fetures indicate that TL harzburgites are residua after melt-assisted partial melting triggered by melt/fluid migration in the hottest, and perhaps deeper, parts of the pristine DM lithosphere. The interpretation of the Pb isotope composition of Group 2 Cpx is not trivial. In analogy with the interpretation proposed for SWIR, it could unravel the occurrence of mantle sources which incorporated ancient crust and failed to homogenise with the DM mantle. Alternatively, it could be the evidence for ancient continental crust of the South America plate dragged down into the mantle by slab motion.
2009
- Invited talk: Scale and nature of the mantle heterogeneities at the Vema Lithospheric Section (Mid Atlantic Ridge 11°N)
[Abstract in Rivista]
Brunelli, Daniele; E., Bonatti; Cipriani, Anna; M., Ligi; M., Seyler; L., Ottolini
abstract
A 26 Ma-long mantle stretch has been sampled at the Vema Lithospheric Section (VLS) (11° N along the MAR), providing a unique opportunity to analyze inside the mantle heterogeneities and unravel their effect on the melting regime looking at correlations between rock geochemistry and the amount of melt produced (crustal thickness). The geochemistry of mantle residua sampled at the base of the VLS reveals an overall positive correlation with the magmatic crustal thickness, in that suggesting a thermal/compositional control of the melting process. However short (sample-) scale heterogeneities appear when considering the difference between the degree of melting inferred from crustal thickness (integrated extracted melt) and the actual degree of melting calculated per each sample on the base of major and trace elements. Accordingly, the isotopic systematics of the peridotites show a sample scale strong variability, averaging close to the MORB value at the Ma scale. The observed discrepancy reveals that some samples are more depleted than the expected average degree of melting, suggesting the presence of mantle parcels that have undergone an ancient depletion event prior the upwelling and incorporation into the subridge melting region. Less depleted parcels are also present. These blobs are possibly the result of spinel-field refertilization at the end of the melting region. However, an intriguing inverse correlation between isotopic and major element systematics suggests that even such heterogeneities could have formed beneath the melting region possibly by local metasomatism that heterogeneously affected the deep mantle. Pyroxenite-derived melts may have reacted and refertilized some mantle portions then driving the subsequent melting process in the main melting region. This process can explain the paradox that the isotopically most depleted samples (those less metasomatised) are also those that record the lowest degree of melting beneath the ridge axis. A major, first-order, heterogeneity appears in the composition of the residual phases allowing to recognize a source discontinuity that cannot be related to the subridge melting event. Mantle samples older than 18.5 Ma have higher cpx Na and Al and lower Ca for a given Mg value than younger samples. Both domains are characterized by a normal mantle depletion trend correlating overall with the produced magmatic crust.
2009
- Present day versus Temporal Heterogeneity of the Subridge Mantle in the Central Atlantic
[Abstract in Rivista]
M., Ligi; E., Bonatti; Brunelli, Daniele; Cipriani, Anna
abstract
Studies of MORB and of MORP (Mid Ocean Ridge Peridotite) show that the oceanic upper mantle is heterogeneous. Long and short wavelength chemical variability has been reported from the Mid Atlantic Ridge. The subridge mantle degree of melting, estimated from MORP mineral chemistry of mantle equilibrated spinel, opx and cpx, as well as from MORB glasses, decreases from the Azores swell at ~40ο N to the equator, in parallel to the decrease of crustal thickness inferred from the near zero-age Mantle Bouguer anomaly. The temporal evolution of this portion of a slow-spreading mid ocean ridge can be studied along seafloor spreading flowlines normal to ridge segments. A lithospheric section exposed between 10ο and 11ο N, south of the Vema Fracture Zone is giving us the opportunity to study how generation of lithosphere at a 80-km long ridge segment evolved since 25 Ma. Gravity data, and MORP-MORB chemistry correlations suggest a steady increase in crustal thickness and in mantle degree of melting from 20 Ma to Present, with superimposed 3-4 Ma oscillations. Variations of degree of melting, peridotite temperature of equilibration and crustal thickness are not proportional to spreading rate, suggesting variations in mantle source composition and a non-purely passive lithosphere formation at ridge axis. The combination of the zero-age axial ridge trend with the 20 Ma to Present trend could be explained by a subaxial hot/fertile mantle flow from the Azores swell toward an equatorial “cold” belt. The equatorial belt, characterized by long offset transforms, is magma starved and nearly free of basaltic crust. Small quantities of basalt, generated mostly in the garnet stability region by low degrees of partial melting, could not be expelled from the mantle, and froze to form a “constipated”, crust free lithosphere. Numerical calculations show a strong decrease of crustal production as a ridge approaches a transform, proportional to slip rate and offset length. When the amount of melt produced is small, the capability of melt to aggregate and to mix on the way to the surface is low; therefore, the chemical and isotopic signatures of preaggregated melts can be detected. Therefore, long-offset RTI's are potential areas to detect short-scale mantle heterogeneities through the study of MORB. Accordingly, basalts sampled in the equatorial Atlantic close to the Romanche transform, show an increase in trace element variability within a single dredge haul approaching the RTI, with wavelengths comparable to those observed in suites of melt inclusions. The correlation between MORB trace elem
2009
- Scale and nature of the mantle heterogeneities at the Vema Lithospheric Section (Mid Atlantic Ridge 11°N)
[Abstract in Rivista]
Brunelli, Daniele; E., Bonatti; Cipriani, Anna; M., Ligi; M., Seyler; L., Ottolini
abstract
A 26 Ma-long mantle stretch has been sampled at the Vema Lithospheric Section (VLS) (11° N along the MAR), providing a unique opportunity to analyze inside the mantle heterogeneities and unravel their effect on the melting regime looking at correlations between rock geochemistry and the amount of melt produced (crustal thickness). The geochemistry of mantle residua sampled at the base of the VLS reveals an overall positive correlation with the magmatic crustal thickness, in that suggesting a thermal/compositional control of the melting process. However short (sample-) scale heterogeneities appear when considering the difference between the degree of melting inferred from crustal thickness (integrated extracted melt) and the actual degree of melting calculated per each sample on the base of major and trace elements. Accordingly, the isotopic systematics of the peridotites show a sample scale strong variability, averaging close to the MORB value at the Ma scale. The observed discrepancy reveals that some samples are more depleted than the expected average degree of melting, suggesting the presence of mantle parcels that have undergone an ancient depletion event prior the upwelling and incorporation into the subridge melting region. Less depleted parcels are also present. These blobs are possibly the result of spinel-field refertilization at the end of the melting region. However, an intriguing inverse correlation between isotopic and major element systematics suggests that even such heterogeneities could have formed beneath the melting region possibly by local metasomatism that heterogeneously affected the deep mantle. Pyroxenite-derived melts may have reacted and refertilized some mantle portions then driving the subsequent melting process in the main melting region. This process can explain the paradox that the isotopically most depleted samples (those less metasomatised) are also those that record the lowest degree of melting beneath the ridge axis. A major, first-order, heterogeneity appears in the composition of the residual phases allowing to recognize a source discontinuity that cannot be related to the subridge melting event. Mantle samples older than 18.5 Ma have higher cpx Na and Al and lower Ca for a given Mg value than younger samples. Both domains are characterized by a normal mantle depletion trend correlating overall with the produced magmatic crust.
2008
- Multi-stage impregnation of the lithospheric mantle at the Andrew Bain FZ (SWIR)
[Poster]
Paganelli, Emanuele; Brunelli, Daniele; Bonatti, E.; Cipriani, Anna; Ligi, M.
abstract
The Southern ridge-transform intersection of Andrew Bain Fracture Zone (ABFZ) is interpreted as a "cold spot" in the mid-ocean ridge system being characterized by a negative thermal anomaly in the oceanic upper mantle. The negative thermal anomaly is associated to the cold-edge effect due to the great age contrast of the active ridge segments. During the oceanic expedition AB06-S23, in 2006, (organized by ISMAR-CNR, Bologna, Italy, and co-financed by PRNA, Italy) with the russian R/V N. Strakhov, several samples of abyssal peridotites have been collected. Textures and modal distribution of the samples have been investigated revealing a multistage impregnation history. Deep spinel-field impregnation assemblages (sp+cpx‚±opx‚±ol) are followed by plagioclase-field patches and mineral trails (pl+cpx‚±ol) and late shallow gabbroic pockets and veins. The major elements mineral chemistry reveals compositional trends of low-P/T subsolidus partial- to-complete re-equilibration undergone by the upper mantle during the upwelling beneath the ridge. These samples have experienced variable degrees of melting and reacted with percolating melts of possible different composition. In particular, samples showing the lowest degrees of melting have interacted with MORB-like melts and pyroxenitic-derived melts in the spinel and plagioclase stability fields. The presence of these two kinds of melts might prove the presence of enriched portions scattered in a normal depleted mantle beneath ocean ridges. MELTS-based runs provide constraints to variable extents of pyroxenitic-derived melt interaction with the mantle source and crystallization at variable depth of the products of such an interaction. Supported by MIUR-PRIN Cofin project 2007
2008
- Sea-floor spreading initiation: constraints from geophysical data of the Thetis Deep, northern Red Sea
[Abstract in Rivista]
Ligi, M.; Bonatti, E.; Bortoluzzi, G.; Brunelli, Daniele; Caratori Tontini, F.; Cipriani, Anna; Cocchi, L.; Cuffaro, M.; Ferrante, V.; Khalil, S.; Mitchell, N. C.; Rasul, N.; Schettino, A.
abstract
A major step in the "Wilson Cycle" is the splitting of a continent and the birth of a new ocean, with the consequent formation of passive plate margins. The transition from a continental to an oceanic rift can be observed today nowhere better than in the Red Sea/Gulf of Aden system. We have carried out during several years a number of expeditions in the axial portion of the Northern Red Sea, in the region where the northernmost nuclei of axial emplacement of oceanic crust can be observed. High resolution multibeam, magnetics, gravity and multichannel seismic reflection surveys from the Thetis Deep revealed rates and modes of initial pulses of sea floor spreading, velocity of S to N axial propagation of the oceanic rift, evolution of initial MORB-type crust and nature of the mantle thermal anomaly that caused the transition from a continental to an oceanic rift. The Thetis deep is made of three en echelon fault-bounded axial basins that are joined together with axial volcanic ridges and a large number of scattered small central volcanoes. The southern basin shows a strong linear magnetic anomaly corresponding to the axial neo-volcanic zone. Two negative symmetric anomalies identified as Matuyama are present in the southernmost part of this basin, suggesting that the emplacement of oceanic crust at this site started roughly 2.5 Ma, with an average half spreading rate of 6 mm/yr. The central sub-basin is also characterized by a strongly magnetic linear neo- volcanic zone that, however, is flanked only by a small, "vanishing" symmetrical negative anomaly suggesting emplacement of oceanic crust not earlier than about 1 Ma. The northern sub-basin does not show a clearly defined linear neo-volcanic zone although it displays a strong central magnetization suggesting initial emplacement of oceanic crust < 0.7 Ma. This pattern implies a south to north time progression of the initial emplacement of oceanic crust within the Thetis system, with a propagation rate of about 20 mm/yr. Gravity data inversions constrained by seismic data reveal that the oceanic crust extends from the axial neo-volcanic ridges toward the master faults of the axial depression with crustal thickness ranging from 4 to 6 km. The increasing thickness of basaltic crust toward the edges of the basin together with higher degree of melting, inferred by the geochemistry of the basaltic glasses, and higher central magnetization of the northernmost and youngest basin suggest a pulse of faster spreading rate at the onset of sea-floor spreading.
2007
- Accretion at a Mid Atlantic Ridge Segment: a 25 million years long story
[Abstract in Rivista]
Ligi, Marco; Bonatti, Enrico; Brunelli, Daniele; Cipriani, Anna
abstract
abs
2007
- Crust-Poor Lithosphere at Cold Spots in the Mid Atlantic and SW Indian Ridges
[Abstract in Rivista]
Brunelli, Daniele; Bonatti, E; Cipriani, Anna; Grindlay N., R; Ligi, M; Paganelli, Emanuele; Sclater, J.
abstract
The Equatorial portion of the Mid Atlantic Ridge is thought to reflect a thermal minimum in the subridge structure, with deeper than normal axial topography underlain by high upper mantle seismic velocities revealed by tomography. This stretch of Ridge is intersected by a number of long offset transforms, the longest being the Romanche (offset ~950 km corresponding to ~50 Myr). As the Mid Atlantic Ridge axis approaches the Romanche transform from the south, it gradually deepens; its rift valley disappears, and, starting roughly 50 km from the transform, the basaltic crust becomes patchy and then disappears, leaving mantle ultramafics outcropping on the sea floor. Modelling the "cold edge" effect of the transform on the axial Ridge segment shows that partial melting of the subridge mantle decreases as the transform is approached. Crust-free lithosphere outcrops continuously for several hundred kilometers in a ~30 km wide belt south of the Romanche, indicating that the present-day lack of crustal production has been prevailing for at least 30 million years. The mantle derived serpentinized peridotites are of two types. The majority of the samples show evidence of strong impregnation by basaltic melts. The mineral chemistry of the samples that are free of impregnation suggests that they have undergone a very low degree of melting. These results suggest a quasi-crust-free lithosphere, produce by a mantle that has undergone little or no partial melting, unable to expel the small quantities of melt it generates. The small quantities of basalt produced in this area tend to have alkali affinity and are strongly enriched in H2O. Their REE content show a strong garnet signature, suggesting that they were generated mostly in the garnet peridotite mantle zone (> 20 kbar). This quasi-crust-free impregnated lithosphere probably prevails at cold spots along mid ocean ridges. Peridotites obtained recently from the SW end of the Andrew Bain transform, that offsets the SW Indian Ridge by ~750 km (~50 Myr), are strongly impregnated by basaltic melt, in a situation very similar to that observed near the Romanche. In contrast, peridotites from the NE end of the Andrew Bain transform are not impregnated, and are residual of a significant degree of melting, probably due to the influence of the Marion plume located a few hundred km away.
2007
- Investigation of the Andrew Bain transform fault zone (African-Antartctic Region)
[Articolo su rivista]
Peyve, A. A.; Skolotnev, S. G.; Ligi, M.; Turko, N. N.; Bonatti, E.; Kolodyazhnyi, S. Y.; Chamov, N. P.; Tsukanov, N. V.; Baramyokov, Y. E.; Eskin, A. E.; Grindlay, N.; Sclater, J. G.; Brunelli, Daniele; Pertsev, A. N.; Cipriani, Anna; Bortoluzzi, G.; Mercuri, R.; Paganelli, Emanuele; Muccini, F.; Takeuchi, C.; Zaffagnini, F.; Dobrolyubova, K. O.
abstract
The Andrew Bain FZ is among the longest oceanicfaults with the active part extending over about 750 km.Since this mid-oceanic ridge (MOR) region is characterizedby very low spreading rates (16 mm/yr), itsactive part is one of the oldest in the whole MOR system. The study of the fault is of great importance forunderstanding the geodynamics and evolution of Circum-Antarctic regions of the World Ocean. Theresults of previous bathymetric and magnetic investigationsand the spatial distribution of earthquakes showedthat the Andrew Bain FZ includes numerous differentsecond-order structures. This feature is typical of continentalstrike-slip fault zones. Such megatransform fault zones can emerge in slowspreading ridges at a relative displacement of the lithosphere, which is thicker and colder than in most transformfaults. The aim of the present work was to substantiatethis suggestion with factual material.
2007
- Leg 209 Summary: Processes in a 20-km-Thick Conductive Boundary Layer beneath the Mid-Atlantic Ridge, 14°-16°NProceedings of the Ocean Drilling Program, 209 Scientific Results
[Capitolo/Saggio]
Kelemen, P. B.; Kikawa, E.; Miller D., J; Abe, N.; Bach, W.; Carlson, R. L.; Casey, J. F.; Chambers, L. M.; Cheadle, M.; Cipriani, Anna; Dick, H. J. B.; Faul, U.; Garces, M.; Garrido, C.; Gee, J. S.; Godard, M. M.; Graham, D. W.; Griffin, D. W.; Harvey, J.; Ildefonse, B.; Iturrino, G. J.; Josef, J.; Meurer, W. P.; Mrozewski, S.; Paulick, H.; Rosner, M.; Schroeder, T.; Seyler, M.; Takazawa,
abstract
This paper provides a summary of postcruise scientific results from Ocean Drilling Program (ODP) Leg 209 available to date, building upon shipboard observations and syntheses summarized in the Leg 209 Initial Results volume. During Leg 209, 19 holes were drilled at 8 sites along the Mid-Atlantic Ridge from 14°43´ to 15°44´N, mainly in residual mantle peridotite intruded by gabbroic rocks, in order to understand the tectonic and structural processes responsible for formation of oceanic lithosphere with abundant residual peridotite exposed on the seafloor coupled with a relatively low proportion of volcanic rocks.Based on proportions of recovered lithologies, the entire area may be underlain by mantle peridotite with ~20%–40% gabbroic intrusions and impregnations. Impregnated peridotites with olivine + two pyroxenes + plagioclase + spinel that apparently formed in equilibrium probably record crystallization from primitive mid-ocean-ridge basalt at pressures of 0.5–0.6 GPa. Metamorphic equilibria record isobaric cooling to ~1100°C at this pressure. Thus, the conductively cooled thermal boundary layer beneath the Mid-Atlantic Ridge in this region is >15 km thick.Combined crystallization and reaction with residual peridotite formed a series of impregnated peridotites recording increasing Na content at nearly constant Mg#; this process could explain some of the variation in fractionation-corrected Na (e.g., Na = 8.0) observed in mid-ocean-ridge basalts. Clinopyroxene textures and compositions record such impregnation processes, and they are particularly well documented for Site 1274. Other Leg 209 gabbroic rocks formed from extensive crystallization of highly evolved melts, indicating that a substantial proportion of melt entering the thermal boundary layer crystallizes entirely beneath the seafloor, with no volcanic equivalent.Alteration of peridotites occurred over a range of temperatures and is the result of three distinct processes: rock-dominated serpentinization with formation of brucite in olivine-rich lithologies, fluid-dominated serpentinization with formation of magnetite and no brucite, and fluid-dominated talc alteration with addition of SiO2 as well as H2O and oxygen. The latter two processes also exhibit detectable trace element metasomatism that is distinct in its character from the igneous impregnation described in the previous paragraph.Microstructures show that most residual peridotites were not ductilely deformed at temperatures less than ~1200°C. Structural and paleomagnetic data require tectonic rotations of relatively undeformed blocks; some rotations probably exceeded 60° around nearly horizontal axes parallel to the rift axis. Rotations occurred along several generations of high-temperature mylonitic shear zones extending deeper than 15 km depth and numerous faults at lower temperature. Early formed shear zones and faults were passively rotated around later features; such a process could have produced low-angle fault surfaces without slip on low-angle faults. This region provides end-member examples of processes that are common at many or most slow-spreading ridges.Osmium isotope ratios indicate an ancient history of depletion for residual peridotites from the 14°–16°N region along the Mid-Atlantic Ridge. Though depleted Os isotope ratios in peridotite have been reported elsewhere along the global ridge system, the values from this region are among the most depleted. In general, Os isotope ratios from mid-ocean-ridge basalts are systematically more radiogenic than Os isotope ratios from ridge peridotite samples, suggesting a polygenetic heterogeneous source for mid-ocean-ridge basalts.Geochemical studies of zircons from Leg 209 gabbroic rocks and impregnated peridotites, together with other ridge and arc-related zircons, indicate that ridge zircons have systematically lower fractionation-corrected U and Th concentrations compared to arc zircons. This observati
2007
- Solid mantle upwelling rate beneath the Mid Atlantic Ridge
[Abstract in Rivista]
Cipriani, Anna; Ligi, M; Bonatti, E; Brunelli, Daniele
abstract
The upwelling velocity of the solid mantle beneath mid ocean ridges affects processes of melting and generation of the oceanic crust, and constrains models of spreading of oceanic plates. Models of passive flow require that the solid mantle rises beneath a ridge at a speed similar to the half spreading rate of the plates. However, increased buoyancy due to melt depletion and melt retention may cause the sub-ridge mantle to rise at a speed much faster than the half spreading rate. In order to constrain these models it is important to estimate the sub- ridge mantle up-welling rate. Such estimates have been attempted in a few cases by measuring in zero-age basalt disequilibria in short lived isotopes produced by the U-decay series. Melt upward migration from the sub-ridge melting zone to the crust is much faster than its parent solid mantle upward flow; therefore, a time lag is created between melt emplacement as basalt in upper lithosphere and emplacement of the parent residual peridotite in the lower lithosphere. We were able to estimate this time lag along a lithospheric sliver, generated at a 80 km long segment (EMAR) of the Mid Atlantic Ridge located between 10° N and 11°N, just south of the Vema transform. The northern edge of this lithospheric sliver exposes crustal and upper mantle units along a 320 km long spreading flowline equivalent to a 26 Myr long time interval. Comparing temporal variations of crustal thickness, inferred from the Residual Mantle Bouguer Anomaly along a flowline starting from the centre of the EMAR segment, to temporal variations of mantle degree of melting, estimated from mineral chemistry of peridotites exposed along the Vema lithospheric section, allowed us to estimate an average solid mantle rising rate of 16.5 mm/yr below the EMAR segment for a time interval from 26 to 2 Ma. This rate is slightly higher than the average half spreading rate of 15.6 mm/yr for the same period. The similarity between average up-welling rate and spreading rate at 11° N on the Mid Atlantic ridge is in line with up-welling estimates obtained by U-series disequilibria, supporting in general a mostly passive mantle flow model. However, temporal variations of spreading rate at 11° N for the last 26 Myr are decoupled from mantle degree of melting and geothermometry estimates, suggesting variations of mantle upwelling rates due to an active component.
2006
- 26 Million Years of mantle upwelling below a segment of the Mid Atlantic Ridge: the Vema Lithosperic Section revisited
[Abstract in Rivista]
Cipriani, Anna; Bonatti, E.; Brunelli, Daniele; Ligi, M.
abstract
An uplifted, relatively undeformed sliver of oceanic lithospheric (Vema Lithospheric Section or VLS), exposing a >26 Myr record of lithosphere generation at a segment of the Mid Atlantic Ridge (EMAR segment, 10°-11°N, central Atlantic), provides the ideal setting to tackle the problem of temporal variations in the processes of creation of oceanic lithosphere at a slow-spreading ridge. A first study, that combined the temporal variations of the mineral chemistry of mantle peridotites sampled along the VLS and gravity measured along a flow line starting from the center of the EMAR segment, detected a steady increase of crustal thickness and of mantle degree of melting from ~20 Ma to 4 Ma before present. Additional sampling was carried out in 2005 along the VLS, extending the coverage of mantle peridotites from a lithospheric age of 26 Ma to 2 Ma. The 26 Ma to 18.5 Ma interval shows short wavelength (~4 Myr) variations of the mantle degree of melting, superimposed on a weak trend of decreasing degree of melting. In the 18.5 to 2 Ma interval a steady increase of degree of melting was observed, with superimposed 3-4 Myr oscillations. Temporal variations of RMBA and crustal thickness inferred from gravity data reveal similar trends. The older (26 to 18.5 Ma) and the younger (18.5 to 2Ma) peridotite suites differ in clinopyroxene CaO/Al2O3 ratio, suggesting that not only the thermal regime, but also the composition of the mantle source might be different in the two suites. Peridotite two-pyroxene geothermometry shows a decreasing trend of the calculated equilibration temperature from 26 Ma to 18.5 Ma ago, followed by a steady increase from 16 Ma to 2 Ma ago, suggesting that the solid mantle upwelling speed varied through time. A ~2 Myr long interval with strongly deformed ultramafic mylonites as the dominant rock type lies between the two opposite trends, as if marking a change in mantle thermal regime. It may reflect a thermal minimum in the subridge upwelling mantle, with nearly a-magmatic emplacement of the lithosphere resulting in strong deformation of the mantle rocks. When upwelling of hot and/or fertile mantle resumes a new cycle starts with injection of igneous crust.
2006
- ANDREW BAIN TRANSFORM: MULTIPLE CONTINENTAL-TYPE TRANSFORM BOUNDARIES AT MID-OCEAN RIDGE
[Poster]
M., Ligi; E., Bonatti; N. R., Grindlay; J., Sclater; S., Skolotnev; A., Peyve; G., Bortoluzzi; Brunelli, Daniele; Cipriani, Anna; R., Mercuri; F., Muccini; Paganelli, Emanuele; F., Zaffagnini; C., Takeuki; Y., Baramykov; N., Chamov; S., Erofeev; A., Eskin; S., Kolodyazhnyy; A., Pertsev; V., Semenov; V., Rastorgyev; N., Tsukanov; N., Turko; V., Yefimov; L., Zotov
abstract
abstract
2006
- Discontinuous melt extraction and weak refertilization of mantle peridotites at the Vema Lithospheric Section (Mid Atlantic Ridge)
[Articolo su rivista]
Brunelli, Daniele; Seyler, M; Cipriani, Anna; Bonatti, E. AND OTTOLINI L.
abstract
Melting processes beneath the Mid-Atlantic Ridge were studiedin residual mantle peridotites sampled from a lithospheric sectionexposed near the Vema Fracture Zone at 11N along the Mid-Atlantic Ridge. Fractional and dynamic melting models were testedbased on clinopyroxene rare earth element and high field strengthelement data. Pure fractional melting (non-modal) cannot accountfor the observed trends, whereas dynamic melting with critical mass porosity <001 fits better the measured values. Observed microtextures suggest weak refertilization with 01–1% quasi-instantaneous or partially aggregated melts trapped during percolation. The composition of the melts is evaluated, together with their provenance, with respect to the garnet–spinel transition. Partial melts appear to be aggregated over short but variable intervals of the melting column.Deep melts (generated within the garnet stability field at the base of the melting column) escape detection, being separated from theresidues by transport inside conduits or fractures. The temporalevolution of the melting process along the exposed section shows a steady increase of mantle temperature from 20 Ma to present.
2006
- From magma-engorged to magma starved “constipated” lithosphere: The Mid Atlantic Ridge from 40°N to the Equator
[Abstract in Atti di Convegno]
Cipriani, Anna; Brunelli, Daniele; M., Ligi; E., Bonatti
abstract
abstract
2006
- Initial emplacement of Oceanic Lithosphere in the northern Red Sea
[Abstract in Rivista]
Ligi, M.; Bonatti, E.; Bortoluzzi, G.; Brunelli, Daniele; Carminati, E.; Cipriani, Anna; Ferrante, V.; Redini, F.; Barbino, G.
abstract
Multibeam, magnetometric and seismic reflection surveys were carried out in 2005 at the Thetis and Nereus axial deeps in the Northern Red Sea, together with bottom rock sampling. The Thetis Deep includes three en- echelon rift valleys that have joint together. Axial neovolcanic zones were observed in each of these rift valleys, together with large number of diffuse small volcanic cones. Both are made of fresh MORB type rocks. The walls of the rift valleys are formed by normal faulting with superimposed salt tectonics. Complex deformation patterns, partly also caused by salt tectonics, were observed at the transfer zone between Thetis and Nereus Deep to the north. We will present some results of this work, and their bearing on ideas on the initial emplacement of the oceanic lithosphere in the Northern Red Sea.
2006
- Snapshots fo the magma plumbing system from melt inclusions and residual peridotites of the Vema Lithospheric Section (MAR 11°N)
[Abstract in Atti di Convegno]
Brunelli, Daniele; R., Clocchiatti; Cipriani, Anna; M., Ligi; E., Paganelli; L., Ottolini; E., Bonatti
abstract
abstract
2006
- TRANSITION FROM A CONTINENTAL TO AN OCEANIC RIFT IN THE NORTHERN RED SEA
[Poster]
E., Bonatti; G., Bortoluzzi; Brunelli, Daniele; V., Ferrante; M., Ligi; M., Lopez Correa; F., Redini; Cipriani, Anna; G., Barbino; E., Carminati; A., Calafato; N. C., Mitchell; B., Sichler; M., Schmidt; N., Rasul; S. N., Al Nomani; F., Bahreth; R. K., Farawati; S. M., Samir; A., Shawky; Y. M., Al Hazmi
abstract
abstract
2005
- Flexural uplift of a lithospheric slab near the Vema Transform (Central Atlantic): timing and mechanisms
[Articolo su rivista]
E., Bonatti; Brunelli, Daniele; W. R., Buck; Cipriani, Anna; P., Fabretti; V., Ferrante; L. GASPERINI AND M., Ligi
abstract
The Vema Transverse Ridge (VTR) is a prominent, long and narrow topographic anomaly that runs for over 300 km along a sea floor spreading flow line south of the Vema transform at 118 N in the Atlantic. It rises abruptly about 140 km from the axis of theMid-Atlantic Ridge (MAR) in ~10 Myr old crust and runs continuously up to ~25 Myr old crust. It reaches over 3 km above the predicted lithospheric thermal contraction level. It is absent in crust younger than 10 Myr; thus, the uplift of the VTR must haveended roughly 10 Ma. The VTR is interpreted as the exposed edge of a flexured and uplifted slab of oceanic lithosphere that wasgenerated at an 80 km long MAR segment. Based on satellite gravimetry imagery this MAR segment was born roughly 50 Ma andincreased its length at an average rate of 1.6 mm/yr. Multibeam data show that the MAR-parallel sea floor fabric south of the VTRshifts its orientation by 58 to 108 clockwise in ~11–12 Myr old crust, indicating a change at that time of the orientation of the MARaxis and of the position of the Euler rotation pole. This change caused extension normal to the transform, followed between 12 and 10 Ma by flexure of the edge of the lithospheric slab, uplift of the VTR at a rate of 2 to 4 mm/yr, and exposure of a lithosphericsection (Vema Lithospheric Section or VLS) at the northern edge of the slab, parallel to the Vema transform. Ages of pelagiccarbonates encrusting ultramafic rocks sampled at the base of the VLS at different distances from the MAR axis suggest that theentire VTR rose vertically as a single block within the active transform offset. A 50 km long portion of the crest of the VTR roseabove sea level, subsided, was truncated at sea level and covered by a carbonate platform. Subaerial and submarine erosion hasgradually removed material from the top of the VTR and has modified its slopes. Spreading half rate of the crust south of thetransform decreased from 17.2 mm/yr between 26 and 19 Ma to ~16.9 mm/yr between 19 and ~10 Ma, to ~13.6 mm/yr from 10 Ma to present. The slowing down of spreading occurred close in time to the change in ridge/transform geometry, suggesting that the two events are related. A numerical model relates lithospheric flexure to extension normal to the transform, suggesting that theextent of the uplift depends on the thickness of the brittle layer, consistent with the observed greater uplift of the older lithospherealong the VTR.
2005
- Water-rich basalts at mid-ocean-ridge cold spots
[Articolo su rivista]
Marco, Ligi; Enrico, Bonatti; Cipriani, Anna; Luisa, Ottolini
abstract
Although water is only present in trace amounts in the suboceanic upper mantle, it is thought to play a significant role inaffecting mantle viscosity, melting and the generation of crust atmid-ocean ridges. The concentration of water in oceanic basaltshas been observed to stay below 0.2wt%, except for water-richbasalts sampled near hotspots and generated by ‘wet’ mantle plumes. Here, however, we report unusually high water contentin basaltic glasses from a cold region of the mid-ocean-ridgesystem in the equatorial Atlantic Ocean. These basalts aresodium-rich, having been generated by low degrees of meltingof the mantle, and contain unusually high ratios of light versusheavy rare-earth elements, implying the presence of garnet in the melting region. We infer that water-rich basalts from suchregions of thermal minima derive from low degrees of ‘wet’melting greater than 60 km deep in the mantle, with minor dilution by melts produced by shallower ‘dry’ melting—a viewsupported by numerical modelling. We therefore conclude thatoceanic basalts are water-rich not only near hotspots, but also at‘cold spots’.
2005
- Weak residual mantle refertilization by partial melts beneath the Mid Atlantic Ridge
[Abstract in Rivista]
Brunelli, Daniele; M., Seyler; Cipriani, Anna; L., Ottolini; E., Bonatti
abstract
abstract
2004
- Discontinuous/episodic partial melt extraction from the melting region beneath the Mid Atlantic Ridge
[Abstract in Rivista]
Brunelli, Daniele; M., Seyler; Cipriani, Anna; L., Ottolini; E., Bonatti
abstract
abstract
2004
- Flexural uplift of a lithospheric slab near the Vema transform (Central Atlantic): timing and mechanism
[Abstract in Rivista]
Ligi, M.; Bonatti, E.; Brunelli, Daniele; Buck, R. W.; Cipriani, Anna
abstract
The Vema Transverse Ridge (VTR) is a prominent, long and narrow topographic anomaly that runs for over 300 km along a sea floor spreading flow line south of the Vema transform at 11ø N in the Atlantic. It rises abruptly about 137 km from the axis of the Mid Atlantic Ridge (MAR) in ~10 My old crust and runs continuously up to ~ 25 My old crust. It reaches over 3 km above the predicted lithospheric thermal contraction level. It is absent in crust younger than 10 My; thus, the uplift of the VTR must have ended roughly 10 My. The VTR is interpreted as the exposed edge of a flexured and uplifted slab of oceanic lithosphere. Multibeam data show that the MAR-parallel seafloor fabric south of the VTR shifts its orientation by 5ø to 10ø clockwise in ~ 11-12 My old crust, indicating a change at that time of the orientation of the MAR axis and of the position of the Euler rotation pole. This change caused extension normal to the transform, followed between 12 and 10 My ago by flexure of the edge of the lithospheric slab, uplift of the VTR at a rate of 2 to 4 mm/yr, and exposure of a lithospheric section (Vema Lithospheric Section or VLS) at the northern edge of the slab, parallel to the Vema transform. Ages of pelagic carbonates encrusting ultramafic rocks sampled at the base of the VLS at different distances from the MAR axis suggest that the entire VTR rose vertically as a single block within the active transform offset. Erosion has gradually removed material from the top of the VTR and has modified its slopes. A numerical model relates lithospheric flexure to extension normal to the transform, suggesting that the extent of the uplift depends on the thickness of the brittle layer, consistent with the observed topography of the VTR. Spreading half rate of the crust south of the transform decreased from 17.2 mm/yr between 26 and 19 My ago to ~16.9 mm/yr between 19 and ~10 My ago, to ~13.6 mm/yr from 10 My ago to present. The slowing down of spreading occurred close in time to the change in ridge/transfo
2004
- ODP Leg 209 drills into mantle peridotite along the mid-Atlantic ridge from 14°N to 16°N
[Articolo su rivista]
Kelemen, P.; Kikawa, E.; Miller, D. J.; Natsue, Abe; Wolfgang, Bach; Richard L., Carlson; John F., Casey; Lynne M., Chambers; Michael, Cheadle; Cipriani, Anna; Henry J. B., Dick; Ulrich, Faul; Miguel, Garces; Carlos, Garrido; Jeffrey S., Gee; Marguerite M., Godard; David W., Graham; Dale W., Griffin; Jason, Harvey; Benoit, Ildefonse; Gerardo J., Iturrino; Jennifer, Josef; William P., Meurer; Stefan, Mrozewski; Holger, Paulick; Martin, Rosner; Timothy, Schroeder; Monique, Seyler; Eiichi, Takazawa
abstract
not available
2004
- Oceanic crust generated by elusive parents: Sr/Nd isotopes in basalt-peridotite pairs from the Mid-Atlantic Ridge
[Articolo su rivista]
Cipriani, Anna; Bruekner, H; Bonatti, E; Brunelli, Daniele
abstract
Given that oceanic basalts form by partial melting of mantle peridotites that rise below mid-ocean ridges, peridotite and basalt should have identical Sr and Nd isotope ratios.We tested this concept on parallel sets of peridotites and basalts sampled from an exposed section of lithosphere representing 20 m.y. of accretion at the Mid-Atlantic Ridge. The 143Nd/144Nd ratios of the basaltic glasses stay constant, whereas those of the peridotitic clinopyroxenes extend both higher and lower than the basalt ratios, suggesting that the constant isotopic composition of the basalts results from mixing of melts released by peridotitesfrom a broad region of the subridge mantle. The degree of melting undergone by the peridotites correlates inversely with their 143Nd/144Nd ratios. Small-scale isotopic heterogeneity of the peridotites may result from variable premelting metasomatism in the mantle, mostly during periodic, dynamic, subridge upwelling, possibly superimposed upon time-integrated radioactive decay of ancient heterogeneities.
2004
- Proceedings of the Ocean Drilling Program, Initial Reports, Volume 209, Drilling mantle peridotite along the Mid-Atlantic Ridge from 14 degrees to 16 degrees N, Sites 1269-1275
[Monografia/Trattato scientifico]
Kelemen, P. B.; Kikawa, E.; Miller D., J; Abe, N.; Bach, W.; Carlson, R. L.; Casey, J. F.; Chambers, L. M.; Cheadle, M.; Cipriani, Anna; Dick, H. J. B.; Faul, U.; Garces, M.; Garrido, C.; Gee, J. S.; Godard, M. M.; Graham, D. W.; Griffin, D. W.; Harvey, J.; Ildefonse, B.; Iturrino, G. J.; Josef, J.; Meurer, W. P.; Mrozewski, S.; Paulick, H.; Rosner, M.; Schroeder, T.; Seyler, M.; Takazawa, E.
abstract
Leg 209 was devoted to drilling mantle peridotites and associatedgabbroic rocks along the Mid-Atlantic Ridge from 14° to 16°N. This area was identified at the 1996 Workshop on Oceanic Lithosphere and Scientific Drilling into the 21st Century (OL Workshop) as the ideal region for drilling of a strike line of short holes to sample the upper mantle in a “magma-starved” portion of a slow-spreading ridge (spreading rate = ~25 km/m.y.). In this area, igneous crust is locally absent and the structureand composition of the mantle can be determined at sites morethan ~100 km apart along strike.A central paradigm of Ridge Interdisciplinary Global Experiments(RIDGE) studies is the hypothesis that mantle flow, or melt extraction, or both, are focused in three dimensions toward the centers of magmatic ridge segments, at least at slow-spreading ridges such as the Mid- Atlantic Ridge. This hypothesis has essentially reached the status of accepted theory, but it has never been subject to a direct test. A strike line of oriented mantle peridotite samples extending for a significant distancewithin magmatic segments offers the possibility of directly testingthis hypothesis. Continued dredging and submersible studies cannot provide the spatial information required to make such a test.The primary aim of drilling was to characterize the spatial variation of mantle deformation patterns, residual peridotite composition, melt migration features, plutonic rocks, and hydrothermal alteration along axis. Hypotheses for focused solid or liquid upwelling beneath ridge segments make specific predictions regarding the spatial variation of mantle lineation or the distribution of melt migration features. These predictions were directly tested by drilling. We discovered that penetrativemantle deformation fabrics are weak at every site where mantle peridotite was sampled from 14°43′N to 15°39′N. Instead, at all of these sites, deformation was localized along high-temperature shear zones and later brittle faults. Intact blocks of peridotite with high-temperature, protogranular fabrics were preserved between these zones of localized deformation and underwent substantial tectonic rotation, perhaps as much as 90° around horizontal, ridge-parallel rotation axes in some places.At most sites, drilling recovered substantial proportions of gabbroic rocks intrusive into mantle peridotite. Some of these rocks have mineral assemblages that are probably indicative of crystallization at depths of 12–20 km beneath the Mid-Atlantic Ridge. Localized deformation at several of these sites occurred preferentially within contact zones between peridotite and these gabbroic intrusions. Abundant gabbroic intrusions were found close to the 15°20' Fracture Zone, at Site 1271, and far from the fracture zone at Sites 1270, 1268, and 1275. Conversely, some holes intersected very little gabbroic material; these were at Site 1272, very close to the fracture zone, and Site 1274, far from the fracture zone. Thus, there is little evidence from the results of this leg for focusing of melt distribution away from the fracture zone and toward the centers of volcanically active ridge segments.
2004
- Small scale mantle heterogeneities sampled through oceanic basalts from ridge-transform intersections
[Abstract in Rivista]
Cipriani, Anna; Bonatti, E.; Brunelli, Daniele; Ligi, M.; Ottolini, L.
abstract
Studies of MORB have shown that the oceanic upper mantle is heterogeneuos. The nature, distribution and scale of these heterogeneities are still a matter of debate. Short-wavelength chemical variability has been observed along mid-ocean ridges. Melt inclusions show isotopic and chemical variabilty within a single basalt sample and even within a single olivine grain. The distance along axis affected by the ridge-transform intersection (RTI) cold edge effect is proportional to slip rate and offset length. Numerical calculations show a strong decrease of crustal production as a ridge approaches a transform. When the amount of melt produced is small, the capability of melt to aggregate and to mix in magma chambers on the way to the surface is low; therefore, the chemical and isotopic signatures of preaggregated melts can be detected. These predictions make long-offset RTI's potential areas to detect chemical variability in the mantle through the study of MORB. Basalts sampled in the equatorial Atlantic along a ridge segment south of the Romanche RTI (ERRS), show an increase in trace element variability within a single dredge haul, with wavelengths comparable to that observed in suites of melt inclusions. This variability implies that melt transport beneath the ERRS is inefficient at mixing melts and suggests melt transport in channelized systems that limit interaction between melt and solid. The correlation between trace element and isotopic enrichement suggests that most of the chemical variability is probably due to source heterogeneity. Melt transport preserves correlations present in the source, suggesting channels nucleation in the deepest part of the molten region just within melting heterogeneities. Correlations will be probably destroyed if channel networks cross source heterogeneities. Volatile-rich low degree partial melts, generated at depth from enriched peridotite or from pyroxenite lumps, react with and metasomatize
2003
- Mantle peridotites from the Bouvet Triple Junction Region, South Atlantic
[Articolo su rivista]
Brunelli, Daniele; Bonatti, E; Cipriani, Anna; Ottolini, L.
abstract
The Bouvet Triple Junction (BTJ) region in the South Atlantic,where the African, South American and Antarctica plates meet,is affected by several topographic ⁄ melting anomalies. Causesof these anomalies were investigated through a study ofmantle-derived serpentinized peridotites sampled from threesites in the BTJ region: (1) the Inner Corner High at theintersection of the America Antarctic Ridge (AAR) with theConrad transform; (2) the south wall of the Bouvet transform(South West Indian Ridge, SWIR); and (3) the eastern BouvetSWIR Transform Intersection. The degree of melting undergone by these rocks was estimated from relic mineral major- and trace-element composition. Geochemical profiles from residual peridotites and associated basalts show a > 1000-km-wide melting anomaly centred on the Bouvet and Spiess topographic anomalies.
2003
- Mantle thermal pulses below the Mid-Atlantic Ridge and temporal variations in the formation of oceanic lithosphere
[Articolo su rivista]
Bonatti, E; Ligi, M; Brunelli, Daniele; Cipriani, Anna; Fabretti, P; Ferrante, V; Gasperini, L; Ottolini, L.
abstract
A 20-Myr record of creation of oceanic lithosphere at a segment of the central Mid-Atlantic-Ridge is exposed along an upliftedsliver of lithosphere. The degree of melting of the mantle that is upwelling below the ridge, estimated from the chemistry ofthe exposed mantle rocks, as well as crustal thickness inferred from gravity measurements, show oscillations of ,3–4 Myrsuperimposed on a longer-term steady increase with time. The time lag between oscillations of mantle melting and crustalthickness indicates that the solid mantle is upwelling at an average rate of ,25mmyr21, but this appears to vary through time.Slow-spreading lithosphere seems to form through dynamic pulses of mantle upwelling and melting, leading not only to along-axissegmentation but also to across-axis structural variability. Also, the central Mid-Atlantic Ridge appears to have become steadilyhotter over the past 20 Myr, possibly owing to north–south mantle flow.The oceanic lithosphere covers two-thirds of our planet: understanding how it forms and evolves is a major challenge in the Earth sciences. It is generally agreed that the oceanic lithosphere forms along mid-ocean ridges, where mantle material upwells and undergoes decompression and partial melting. The melt rises rapidly and freezes, producing the crust, while the peridotitic residue forms the lithospheric mantle. Mid-ocean-ridge topography, structure and composition indicate that near zero age processes of lithosphere formation vary along ridge axis1–3. Less is known, however, of how these processes vary through time, a question important for our understanding of how ocean basins evolve. Variations through time of the thermal regime and/or composition of a mid-ocean ridge should be recorded in lithosphere lying at increasing distances from the ridge axis along sea-floor spreading flow lines. However, older lithosphere is normally covered by sediment and not easily accessibleto high-resolution observation and sampling.An uplifted sliver of oceanic lithosphere (Fig. 1), exposing in thecentral Atlantic an ,20-Myr-long record of creation of lithosphereat a segment of the Mid-Atlantic Ridge (MAR), gave us theopportunity to investigate the temporal variability in the formationof lithosphere, to estimate the upwelling velocity of the mantlebelow the ridge, and to determine whether passive or dynamicmodels of creation of oceanic lithosphere prevail at slow-spreadingridges. A sliver of exposed oceanic lithosphere A major topographic anomaly, the Vema transverse ridge, runs onthe southern side of the Vema transform, which offsets the MAR by 310 km at ,118N (Fig. 1). Its exposed northern scarp (that is, the southern wall of the transform valley) reaches in height up to 4 km above the valley floor (Fig. 2). Submersible4, multibeam5 and seismic reflection data, and bottom samples (Fig. 1) revealed that the northern side of the Vema transverse ridge exposes a ,3–4-km thick, relatively complete and tectonically undeformed upperlithospheric
2002
- Is the Mid-Atlantic Ridge becoming hotter with time?
[Poster]
Bonatti, E.; Ligi, M.; Brunelli, Daniele; Cipriani, Anna; Gasperini, L.
abstract
More than 20 million years of oceanic lithosphere accretion history at a segment of the Mid-Atlantic Ridge are recorded in the Vema Lithospheric Section (VLS), a 300 km long flexured and uplifted sliver of lithosphere exposed near the Vema Fracture Zone in the Central Atlantic. Systematic sampling of the basal mantle ultramafic unit and of crustal basalts along the VLS together with geophysical surveys gave us the opportunity to study temporal changes in the processes of generation of the oceanic lithosphere at a ridge axis. The degree of melting of the mantle upwelling below the ridge axis, estimated from the chemistry of mantle-equilibrated mineral phases in the peridotites, as well as crustal thickness, inferred from shipboard and satellite gravity data, both show ~3-4 my long oscillations superimposed on long-range steady increases with time. Based on basaltic glasses elemental and isotopic chemistry, we assume the composition of the source stayed nearly constant. The steady increase with time of mantle degree of melting and of crustal thickness suggests that the mantle rising beneath the MAR became gradually hotter during the last 20 million years, even though the spreading half rate slowed significantly during this time. We offer two explanations for the increase in mantle temperature with time at the Mid-Atlantic Ridge. A first possibility, of local significance, calls for gradual lengthening of the eastern MAR segment where the VLS was created, leading to an increasing degree of melting below center of the segment as it lengthens, due to the a decreasing influence of the "cold edge effect" from the Vema transform. The second, of broader significance, calls for a gradual increase of mantle potential temperature along a significant portion of the northern MAR during the last 20 million years, resulting in an increase of melt production despite decreasing spreading rates. This second hypothesis is supported by an increase of crustal thickness towards ridge axis observed at several other locations in the northern MAR. The chemistry of basaltic glasses, collected along the VLS above the peridotites, suggests that no deep plume source is involved in the steady heating of the Ridge.
2001
- Structure peculiarities of the Sierra Leone fracture zone (central Atlantic)
[Articolo su rivista]
A. A., Peyve; K. O., Dobrolhybova; V. N., Efimov; Cipriani, Anna; Marco, Ligi; A. O., Mazarovich; A. S., Perfil'Ev; Raznitsyn, Y. u. N.; G. N., Savel'Eva; V. A., Simonov; S. G., Skolotnev
abstract
in russian
2001
- Temporal variations in the mantle source of MORB near the Vema fracture zone (Central Atlantic): Nd and Sr isotopes in peridotite and basaltic glasses
[Poster]
Cipriani, Anna; Brunelli, Daniele; Brueckner, H. K.; Bonatti, E.
abstract
Sr-Nd-Pb isotopic ratios of zero age basalts sampled along Mid-Ocean Ridges (MOR) have demonstrated that the mantle is heterogeneous at a regional scale. However, how the mantle evolves through time below a single segment of MOR it is still matter of debate. Peridotites and basaltic glasses were collected along a lithospheric section uplifted and exposed on the southern side of the Vema transform (10$^{\circ}$ North, Atlantic Ocean) along a seafloor spreading flow line for a stretch of almost 200 km (corresponding to roughly 10 my). This set of samples offers a unique opportunity to detect changes through time of the mantle signature in a segment of Mid Atlantic Ridge, by analyzing radiogenic isotopes in the clinopyroxenes (cpx) from peridotites and glasses from the overlying basalts. Work is in progress; initial Sr and Nd measurements from cpxs within peridotites indicate several things. First, the cpxs display "depleted" mantle signatures. Second, there is a considerable variation of the isotopic ratios along the exposed section ($^{143}$Nd/$^{144}$Nd varies from 0.51293 to 0.51345, $^{87}$Sr/$^{86}$Sr varies from 0.70228 to 0.70422) and these variations occur over a short time scale (some occur within an interval of one million year). Next, the Sr and Nd ratios are inversely correlated and fall along the mantle array. Finally, cpx Nd ratios are inversely correlated with the Cr/Al ratio of the spinel and ortopyroxene (opx) from the peridotites while Sr ratios are positively correlated. Thus, the chemically most depleted peridotite with high Cr/Al ratios show the most enriched isotopic signatures, a pattern that has also been observed in alpine-type peridotites and peridotite nodules and that is generally interpreted as metasomatism by enriched fluids affecting depleted peridotite more extensively than less depleted peridotite. This may indicate that the temporal variations in the extent of melting detected by Cr/Al ratio in spinel and opx (Bonatti et al., Variations with age of mantle ultramafic composition near the Vema Fracture Zone, Central Atlantic. EOS, Vol.79, No.45, F919) are related to rapid changes in the degree of depletion of the upwelling mantle sources and that the degree of depletion of these mantle sources is an inherited feature from earlier processes rather than the result of melting at the MOR.
1999
- La struttura termica del mantello oceanico e la creazione della litosfera oceanica nell’Atlantico centrale e meridionale
[Abstract in Rivista]
Bonatti, E.; Gasperini, L.; Ligi, M.; Brunelli, Daniele; Cipriani, Anna; Fabretti, P.
abstract
abstract
1999
- Spatial and temporal heterogeneity of the oceanic mantle in the Central Atlantic
[Relazione in Atti di Convegno]
Bonatti, E.; Brunelli, Daniele; Cipriani, Anna; Ottolini, L.; Seyler, Monique
abstract
Studies of Mid Ocean Ridge Peridotites (MORP) sampled from the Kane (24°N) to the Chain (2°S) transforms in the Central Atlantic reveal upper mantle domains with different composition and subjected to different thermal conditions and degrees of melting along this stretch of mid ocean ridge. These different domains include thermal minima (“cold spots”), such as observed in the equatorial area, and thermal maxima (mini-“hot spots”). Zero-age topography, gravimetry and seismic tomography support the concept of along axis mantle thermal and/or compositional heterogeneity. Close spaced sampling profiles of mantle-derived peridotites were obtained along seafloor spreading flow lines at two Latitude (0° and 11°N). These profiles indicate significant temporal variations in the composition and thermal structure of the oceanic mantle, and of processes of lithosphere creation at ridge axis.
1999
- The Bouvet melt anomaly in the South Atlantic: geochemistry and influence on the Triple Junction Geometry
[Abstract in Rivista]
Brunelli, Daniele; Cipriani, Anna; Ottolini, L.; Vaggelli, G.; Santo, A. P.; Bonatti, E.
abstract
abstract
1999
- Time constraints on the emplacement of an uplifted sliver of oceanic lithosphere at the Vema transverse ridge (Central Atlantic)
[Abstract in Rivista]
Gasperini, L.; Bonatti, E.; Borsetti, A. M.; Brunelli, Daniele; Capotondi, L.; Carrara, G.; Cipriani, Anna; Fabretti, P.; Ligi, M.; Kastens, K.
abstract
The Vema fracture zone is the northernmost of a set of major transform faults which displace the Mid Atlantic Ridge (MAR) at 10°50' N by over 320 km. It is paralleled on its southern flank by a prominent transverse ridge, the summit of which shoals up to 450 m below the sea level near the western ridge transform intersection. The north facing wall of the Vema transverse ridge exposes a relatively complete and undisturbed sliver of upper oceanic lithosphere. Consolidated pelagic limestones locally encrust the exposed igneous rocks, while shallow water carbonate platforms, up to 600 m thick, cap the summit of the transverse ridge. The Vema transverse ridge originated by vertical movements that have uplifted a flexured sliver of oceanic lithosphere. Multichannel seismic reflection profiles taken across the transverse ridge and the transform valley give evidence of recent transpression in the valley, and of extension across the transverse ridge and in the area south of it. Vertical movements might be due to these transpressive and transtensional stresses, related to small changes in spreading direction. Pelagic, as well as shallow water limestones recovered from the transverse ridge, will provide age constraints on the emplacement history of the lithospheric sliver exposed on the transverse ridge.
1999
- Vema Fracture Zone (Central Atlantic): Temporal variations of mantle composition and of accretion processes at ridge axis
[Abstract in Rivista]
Brunelli, Daniele; Cipriani, Anna; Ottolini, L.; Bonatti, E.
abstract
The Vema Fracture Zone in the Central Atlantic offers a unique opportunity for studying how the processes of formation of oceanic lithosphere vary with time. An uplifted, relatively complete and undisturbed section of oceanic upper lithosphere is exposed on the southern wall of the transform valley along a seafloor spreading flow line for a distance of about 300 km corresponding to almost 20 m.y. (if we assume an average spreading half-rate of 15 mm/y). Close spaced sampling (at 6-8 km horizontal intervals) of the basal portion of this exposed lithospheric section, for a stretch of almost 200 km, produced a set of mantle-derived peridotites serpentinized to various degrees. These samples preserve relicts of mantle-equilibrated "primary" phases such as olivine, opx, cpx and spinel and give us the opportunity of studying temporal variations of the composition of the mantle for a ~10 m.y.-long interval of time. The peridotites are mostly protogranular or porphyroclastic harzburgites and lherzolites. In a portion of the lithospheric sliver, corresponding to a 2-m.y. time interval, the ultramafic rocks are strongly deformed with amphibole-bearing mylonites prevailing. Preliminary electron and ion probe data on major and trace element chemistry of the mantle-equilibrated minerals in porphyroclastic peridotites, show significant compositional variations with age. For example, the Cr/Al ratio of spinel and the Al2O3 content of opx vary systematically with distance from ridge axis, suggesting both long- (several m.y.) and short- (< 1 m.y.) wavelength systematic variations in the composition and degree of melting of the upwelling mantle. These variations probably relate to systematic temporal changes of the thermal structure of the mantle below the Mid-Atlantic Ridge. Stretches of the lithospheric sliver where amphibole-bearing ultramafic mylonites are dominant may correspond to intervals of prevalent a-magmatic extension at ridge axis.
1998
- Contrasting Ultra-Slow Ridges near the Bouvet Triple Junction in the South Atlantic
[Abstract in Rivista]
Ligi, M.; Bonatti, E.; Brueckner, H. K.; Brunelli, Daniele; Cipriani, Anna; Fabretti, P.; Ottolini, L.
abstract
Two ultraslow mid ocean ridges, i.e., the westernmost portion of the Southwest Indian Ridge (SWIR) and the easternmost portion of the American-Antarctic Ridge (AAR), meet the southernmost portion of the Mid Atlantic Ridge (MAR) at the Bouvet Triple Junction. Although both the SWIR and the AAR have very slow spreading rates, i.e., 7.5 mm/y and 10 mm/y, respectively, they display strongly contrasting morphostructural and petrological characteristics. The AAR axial zone is deeper than normal (>4000m); some of its segments are oblique, being oriented roughly 45 degrees from the direction of spreading; basalt and peridotite chemistry suggests a relatively low degree of melting of the mantle below the AAR. In contrast, the SWIR axial zone is shallower than normal ($<$2500m); the last segment (Spiess Ridge) is particularly anomalous, reaching ~400 m below sea level. Basalt and peridotite chemistry of this portion of SWIR suggests high extents of melting of the upper mantle. The H2O content of the SWIR basaltic glasses ranges between 0.6% and 1.0% and is significantly higher than in normal MORB. The high extent of melting at the SWIR segments is probably related not only to a mantle thermal anomaly, but also to its high volatiles content. Mantle thermal structure and composition, rather than spreading rate, are the main factors determing the structure of these ridges.
1998
- First results of cruise S19 (PRIMAR project): Petrological and structural investigations of the Vema transverse ridge (equatorial Atlantic)
[Articolo su rivista]
Paola, Fabretti; Enrico, Bonatti; Alexander, Peyve; Brunelli, Daniele; Cipriani, Anna; Xsenia, Dobrolubova; V., Efimov; S., Erofeev; Luca, Gasperini; J., Hanley; Marco, Ligi; A., Perfiliev; V., Rastorguyev; Y., Raznitsin; Galina, Savelieva; V., Semjenov; V., Simonov; S., Sokolov; S., Skolotnev; S., Susini; I., Vikentyev
abstract
We carried out in January-March 1998 a geological-geophysical cruise to the Vema fracture zone that offsets by 320 km the Mid Atlantic Ridge in the central Atlantic. This expedition (S19) was part of PRIMAR (Russian-Italian Mid Atlantic Ridge Project). The field work aimed at obtaining geophysical and petrological data from a prominent transverse ridge that runs on the southern side of the transform valley and constitutes a major topographic anomaly relative to the depth/square root of age relationship. Previous work had shown that a relatively undisturbed section of oceanic lithosphere is exposed on the northern side of the transverse ridge for roughly 270 km along a seafloor spreading flow line. Given an average spreading half rate of 16 mm/y, this length corresponds to over 16 My. One of the objectives of our expedition was to sample at close-spaced (~5 km) horizontal intervals the mantle ultramafic basal unit, in order to detect temporal variations of mantle composition and of accretion processes at ridge axis. Preliminary observations on ultramafic rock samples obtained at 35 sites suggest strong temporal variations of mantle structure and composition. Multichannel seismic reflection profiles were carried out in order to understand the processes that uplifted the transverse ridge and exposed the sliver of oceanic lithosphere. Magnetometric profiles were made to better constrain spreading rates.
1998
- Variations with age of ultramafic composition near the Vema fracture zone, Central Atlantic
[Abstract in Rivista]
Bonatti, E.; Brunelli, Daniele; Cipriani, Anna; Fabretti, P.; Gasperini, L.; Ligi, M.; Peyve, A.; Savelieva, G.; Skolotnev, S.; Susini, S.
abstract
A relatively undisturbed sliver of oceanic lithosphere is exposed on the sea floor for a distance of about 300km along a sea floor spreading flow line near the Vema Fracture Zone in the Central Atlantic. Assuming a spreading half-rate of 15mm/y, the exposed lithospheric sliver represents an almost 20 m.y. time interval of accretion at the axis of the Mid-Atlantic Ridge. The basal, mantle ultramafic unit of this lithospheric section was sampled at close-spaced (~6-8 km) intervals for a stretch of almost 200 km, corresponding to roughly 13 m.y. of accretion. A study of these samples, which is in progress, will give us information on temporal variation of the thermal structure and composition of the upper mantle below a segment of the Mid-Atlantic Ridge. The first results, involving the major and trace element composition of mantle-equilibrated minerals; olivine, orthopyroxene, clinopyroxene and spinel in porphyroclastic peridotites suggest both long (several m.y.) and short ($<$ 1m.y.) wavelength systematic variations that reflect temporal variations in the composition and extent of melting of the mantle below the Mid-Atlantic Ridge. Anphibole-bearing ultramafic mylonites are dominant in a stretch of the section roughly corresponding to a 2 m.y. time interval, that may correspond to a period of prevalent a-magmatic extension at ridge axis.
1997
- Death and transfiguration of a triple junction in the south Atlantic
[Poster]
Ligi, M.; Bonatti, E.; Bortoluzzi, G.; Carrara, G.; Fabretti, P.; Penitenti, D.; Terenzoni, M.; Brunelli, Daniele; Cipriani, Anna; Gilod, D.; Peyve, A. A.; Skolotnev, S.; Turko, N.
abstract
abstract
1997
- Morphostructural analysis of the western intersection of the mid Atlantic ridge with the Romanche transform (equatorial Atlantic)
[Poster]
Bonatti, E.; Gasperini, L.; Ligi, M.; Carrara, G.; Chierici, F.; Fabretti, P.; Susini, S.; Tartarotti, P.; Brunelli, Daniele; Cipriani, Anna; Gilod, D.; Peyve, A. A.; Skolotnev, S.; Turko, N.
abstract
abstract
1997
- New data on the geology of the Romanche F.Z., equatorial Atlantic: PRIMAR-96 cruise report
[Articolo su rivista]
Luca, Gasperini; Enrico, Bonatti; Brunelli, Daniele; Gabriela, Carrara; Cipriani, Anna; Paola, Fabretti; Dolores, Gilod; Marco, Ligi; Alexander, Peyve; Sergey, Skolotnev; Sara, Susini; Paola, Tartarotti; Natasha, Turko
abstract
An oceanographic expedition was carried out in May and June 1996 with the R/V Gelendzhik to the Romanche Fracture Zone (F.Z.), in the frame of an Italian-Russian joint program for the geological study of the equatorial Atlantic (PRIMAR). We present here a cruise report, with some preliminary data and scientific results. The choice of the ship was determined mostly by the availability of a new, state of the art oceanic multibeam system (SIMRAD EM-120-S). The '96 expedition focused on the Romanche F.Z. western ridge/transform intersection (RTI) and complemented a 1994 expedition that covered the eastern RTI. Multichannel seismic reflection, gravimetric and magnetometric profiles were collected, as well as bottom rock samples. Moreover, we acquired over 10,000 nautical miles of high resolution multibeam bathymetry. With these new data the entire active part of the Romanche transform (> 900 km) has been covered by multibeam morphobathymetry.
1997
- The Bouvet Triple Junction Region (south Atlantic): A report on two geological expeditions
[Articolo su rivista]
Gabriela, Carrara; Giovanni, Bortoluzzi; Nevio, Zitellini; Enrico, Bonatti; Brunelli, Daniele; Cipriani, Anna; Paola, Fabretti; Luca, Gasperini; Marco, Ligi; Daniela, Penitenti; P. F., Sciuto; A., Mazarovich; A., Peyve; N., Turko; S., Skolotnev; D., Gilod
abstract
The Bouvet Triple Junction is located where the Antarctic, south American and African plates meet in the south Atlantic. Two oceanographic expeditions were carried out in this region in 1994 and 1996 by the Institute of Marine Geology, CNR (Bologna), and the Geology Institute of the Russian Academy of Science (Moscow) under the sponsorship of the Italian Antarctic Research Program (PNRA). The main objectives of these expeditions were to define the structural, morphological and petrographical differences of the three divergent margins that meet in the Bouvet region, and to clarify the evolution in space and time of the geometry of the Triple Junction. Single and multichannel seismic reflection, gravimetric and magnetometric profiles were obtained during the first cruise, with the R/V Akademik Strakhov, in addition to medium resolution multibeam bathymetry of the Bouvet island area and in the southern portion of the Mid Atlantic Ridge. The second cruise, carried out with the R/V Gelendzhik, completed the bathymetric survey of the entire Triple Junction region using an high resolution multibeam system. Seafloor sampling was carried out by dredging in both cruises. Some of the data obtained during these two expeditions are reported in this paper.