Foto personale

Anna CIPRIANI

Department of Chemical and Geological Sciences

Ligi, Marco; Bonatti, Enrico; Bosworth, William; Cai, Yue; Cipriani, Anna; Palmiotto, Camilla; Ronca, Sara; Seyler, Monique ( 2018 ) - Birth of an ocean in the Red Sea: Oceanic-type basaltic melt intrusions precede continental rupture - GONDWANA RESEARCH - n. volume 54 - pp. da 150 a 160 ISSN: 1342-937X [Articolo in rivista (262) - Articolo su rivista]
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.

Argentino, Claudio; Lugli, Federico; Cipriani, Anna; Conti, Stefano; Fioroni, Chiara; Fontana, Daniela ( 2018 ) - Constraining the fluid source of Miocene seep carbonates using radiogenic Sr isotopes (Corella outcrop, northern Apennines, Italy) - Geophysical Research Abstracts - n. volume 20 [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
Abstract

Analisi isotopiche e biostratigrafiche su corpi carbonatici metanoderivati dell'Appennino settentrionale

Giovanardi, Tommaso; Mazzucchelli, Maurizio; Lugli, Federico; Girardi, Vicente A. V.; Correia, Ciro T.; Tassinari, Colombo C. G.; Cipriani, Anna ( 2018 ) - Isotopic constraints on contamination processes in the Tonian Goiás Stratiform Complex - LITHOS - n. volume 310-311 - pp. da 136 a 152 ISSN: 0024-4937 [Articolo in rivista (262) - Articolo su rivista]
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.

Brunelli, Daniele; Cipriani, Anna; Bonatti, Enrico ( 2018 ) - Thermal effects of pyroxenites on mantle melting below mid-ocean ridges - NATURE GEOSCIENCE - pp. da 1 a 6 ISSN: 1752-0908 [Articolo in rivista (262) - Articolo su rivista]
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.

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 ( 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 - PLOS ONE - n. volume 13 - pp. da 1 a 25 ISSN: 1932-6203 [Articolo in rivista (262) - Articolo su rivista]
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.

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. ( 2017 ) - A global reference database of crowdsourced cropland data collected using the Geo-Wiki platform - SCIENTIFIC DATA - n. volume 4 - pp. da 1 a 10 ISSN: 2052-4463 [Articolo in rivista (262) - Articolo su rivista]
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.

Weber, Michael; Lugli, Federico; Jochum, Klaus Peter; Cipriani, Anna; Scholz, Denis ( 2017 ) - Calcium Carbonate and Phosphate Reference Materials for Monitoring Bulk and Microanalytical Determination of Sr Isotopes - GEOSTANDARDS AND GEOANALYTICAL RESEARCH - pp. da 77 a 89 ISSN: 1639-4488 [Articolo in rivista (262) - Articolo su rivista]
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.

Lugli, Federico; Cipriani, Anna ( 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 - MICROCHEMICAL JOURNAL - n. volume 133 - pp. da 67 a 69 ISSN: 0026-265X [Articolo in rivista (262) - Articolo su rivista]
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.

Lugli, Federico; Brunelli, Daniele; Cipriani, Anna; Bosi, Giovanna ( 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) - ARCHAEOMETRY - pp. da 1119 a 1134 ISSN: 0003-813X [Articolo in rivista (262) - Articolo su rivista]
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.

Lugli, Federico; Cipriani, Anna; Peretto, Carlo; Mazzucchelli, Maurizio; Brunelli, Daniele ( 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 - INTERNATIONAL JOURNAL OF MASS SPECTROMETRY - n. volume 412 - pp. da 38 a 48 ISSN: 1387-3806 [Articolo in rivista (262) - Articolo su rivista]
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.

Cipriani, Anna; Brunelli, Daniele ( 2017 ) - Mantle-Crust Isotopic Relationships along Mid Ocean Ridges: Constraints from the Analysis of Time Series - Goldschmidt Abstracts [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Giovanardi, Tommaso; Cipriani, Anna; Lugli, Federico; Morishita, Tomoaki; Zanetti, Alberto; Mazzucchelli, Maurizio ( 2017 ) - Melt-Rock Interaction at Mantle Conditions: Evidences from Finero Gabbroic Dykes - Goldschmidt Abstracts [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Vescogni, Alessandro; Bosellini, Francesca Romana; Vertino, Agostina; Harzhauser, Mathias; Mandic, Oleg; Cipriani, Anna; Conti, Stefano; Remitti, Francesca ( 2017 ) - Miocene phosphatic hardgrounds of the Mediterranean and their biotic assemblage: new insights from the "Aturia level" of the Salento Peninsula (S. Italy) - Volume dei Riassunti - pp. da 70 a 71 ISSN: - [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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

Giovanardi, Tommaso; Girardi, Vicente A.V.; Correia, Ciro T.; Tassinari, Colombo C.G.; Sato, Kei; Cipriani, Anna; Mazzucchelli, Maurizio ( 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 - LITHOS - n. volume 282-283 - pp. da 339 a 357 ISSN: 0024-4937 [Articolo in rivista (262) - Articolo su rivista]
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.

Brunelli, Daniele; Cipriani, Anna ( 2017 ) - Pyroxenites sow discord between parent mantle and daughter MORB - Goldschmidt Abstracts [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Lugli, Federico; Cipriani, Anna; Tavaglione, Valentina; Traversari, Mirko; Benazzi, Stefano ( 2017 ) - Strontium Isotope MC-ICP-MS Analysis of Hair Strands from Human Mummies: Transhumance Pastoralism of Early-Modern Individuals between Northern and Central Italy - Goldschmidt Abstracts [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Lugli, Federico; Cipriani, Anna; Arnaud, Julie; Arzarello, Marta; Peretto, Carlo; Benazzi, Stefano ( 2017 ) - Suspected limited mobility of a Middle Pleistocene woman from Southern Italy: strontium isotopes of a human deciduous tooth - SCIENTIFIC REPORTS - n. volume 7 - pp. da 1 a 8 ISSN: 2045-2322 [Articolo in rivista (262) - Articolo su rivista]
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.

Gasperini, Luca; Bonatti, Enrico; Borsetti, Anna Maria; Capotondi, Lucilla; Cipriani, Anna; Negri, Alessandra ( 2017 ) - Timing of transverse ridge uplift along the Vema transform (Central Atlantic) - MARINE GEOLOGY - n. volume 385 - pp. da 228 a 232 ISSN: 0025-3227 [Articolo in rivista (262) - Articolo su rivista]
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.

Lugli, F.; Cipriani, A.; Mazzucchelli, M.; Sforna, M.C.; Brunelli, D. ( 2016 ) - In situ 87Sr/86Sr LA-MC-ICPMS on biogenic apatites: a matrix-matched standard correction approach - Goldschmidt Conference Abstracts - pp. da 1904 a 1904 ISSN: - [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Mazzucchelli, Maurizio; Cipriani, Anna; Hémond, Christophe; Zanetti, Alberto; Bertotto, Gustavo Walter; Alberto, Cingolani. Carlos ( 2016 ) - Origin of the DUPAL anomaly in mantle xenoliths of Patagonia (Argentina) and geodynamic consequences - LITHOS - n. volume 248-251 - pp. da 257 a 271 ISSN: 0024-4937 [Articolo in rivista (262) - Articolo su rivista]
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.

Lugli, F.; Giovanardi, T; Girardi, V.A.V.; Correla, C.T.; Tassinari, C.C.G.; Sinigoi, S.; Cipriani, A.; Mazzucchelli, M. ( 2016 ) - PRELIMINARY U-Pb LA-ICPMS ZIRCON ANALYSES FROM THE GOIAS COMPLEXES: SHRIMP COMPARISON AND INTRUSION AGE - PLINIUS - n. volume 42 - pp. da 764 a 764 ISSN: 1972-1366 [Abstract in rivista (266) - Abstract in Rivista]
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.

Borghini, Giulio; Rampone, Elisabetta; Zanetti, Alberto; Class, Cornelia; Cipriani, Anna; Hofmann, Albrecht W.; Goldstein, Steven L. ( 2016 ) - Pyroxenite Layers in the Northern Apennines’ Upper Mantle (Italy)—Generation by Pyroxenite Melting and Melt Infiltration - JOURNAL OF PETROLOGY - pp. da 1 a 29 ISSN: 0022-3530 [Articolo in rivista (262) - Articolo su rivista]
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.

Giovanardi, T.; Lugli, F.; Girardi, V.A.V.; Correla, C.T.; Tassinari, C.C.G.; Sinigoi, S.; Cipriani, A.; Mazzucchelli, M. ( 2016 ) - THE LARGE LAYERED GOIAS COMPLEXES: NEW U-Pb ANO PRELIMINARY Lu-Hf IN SITU ZIRCON ANALYSES FROM BARRO ALTO AND CANA BRAVA - PLINIUS - n. volume 42 - pp. da 756 a 756 ISSN: 1972-1366 [Abstract in rivista (266) - Abstract in Rivista]
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.

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 ( 2015 ) - Building a hybrid land cover maps with crowdsourcing and geographically weighted regression - ISPRS JOURNAL OF PHOTOGRAMMETRY AND REMOTE SENSING - n. volume 103 - pp. da 48 a 56 ISSN: 0924-2716 [Articolo in rivista (262) - Articolo su rivista]
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).

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. ( 2015 ) - Discovering Past Gut Microbiomes Through Ngs Analysis: The Mummies Of Roccapelago (MO) - Abstract eBook of Evoluzione2015 - EDISES ) [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Lugli, Federico; Cipriani, Anna; Reghizzi, Matteo; Brunelli, Daniele; Benazzi, Stefano ( 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 - XXI Congress of the Italian Anthropological Association [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Federico, Lugli; Anna, Cipriani; Daniele, Brunelli; Giorgio, Gruppioni; Maurizio, Mazzucchelli ( 2015 ) - In situ trace element analysis of human hard tissues by Laser Ablation ICP–MS - TRACE ELEMENTS BETWEEN DEFICIENCY AND TOXICITY: UPDATE AND PERSPECTIVES - pp. 39 ISSN: - [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

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 ( 2015 ) - Mapping global cropland and field size - GLOBAL CHANGE BIOLOGY - n. volume 21 - pp. da 1980 a 1992 ISSN: 1365-2486 [Articolo in rivista (262) - Articolo su rivista]
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.

Ligi, Marco; Bonatti, Enrico; Bosworth, William; Cai, Yue; Cipriani, Anna; Palmiotto, Camilla; Rasul, Najeeb; Ronca, Sara; Sanfilippo, Alessio; Seyler, Monique; Nomani, S.; Alqutub, A.. ( 2015 ) - Oceanization starts from below during continental rupturing in the northern Red Sea - EOS Trans. AGU - AGU Washington USA ) [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Ligi, M.; Bonatti, E.; Bosworth, W; Cai, Y.; Cipriani, Anna; Palmiotto, P.; Ronca, S.; Sanfilippo, A.; Seyler, M. ( 2015 ) - Oceanization starts from below during continental rupturing in the Red Sea - Rendiconti Online della Societa' Geologica Italiana - n. volume 35 - pp. 47 ISSN: - [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
Abstract

Oceanization starts from below during continental rupturing in the Red Sea

Pertsev, Alexey N.; Aranovich, Leonid Y.; Prokofiev, Vsevolod Y.; Bortnikov, Nikolay S.; Cipriani, Anna; Simakin, Sergey S.; Borisovskiy, Sergey E. ( 2015 ) - Signatures of residual melts, magmatic and seawater-derived fluids in oceanic lower-crust gabbro from the vema lithospheric section, central Atlantic - JOURNAL OF PETROLOGY - n. volume 56 - pp. da 1069 a 1088 ISSN: 0022-3530 [Articolo in rivista (262) - Articolo su rivista]
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.

Lugli, F.; Brunelli, D.; Cipriani, A.; Bosi, G.; Gruppioni, G. ( 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 - XXI Congresso AAI (Associazione Antropologica Italiana) - Università di Bologna Bologna ITA) - pp. da 107 a 107 ISSN: - [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Bonatti, Enrico; Cipriani, Anna; Lupi, Luca ( 2015 ) - The Red Sea: Birth of an Ocean - The Red Sea: The Formation, Morphology, Oceanography and Environment of a Young Ocean Basin - Springer-Verlag Berlin Heidelberg DEU) - pp. da 29 a 44 ISBN: 9783662452011 ISSN: 2197-9596 [Contributo in volume (Capitolo o Saggio) (268) - Capitolo/Saggio]
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.

Borghini, G; Rampone, E; Zanetti, A; Class, C; Cipriani, Anna; Hofmann, A.W.; Goldstein, S.L.; Godard, M ( 2014 ) - Chemical and isotopic heterogeneity in meter-scale pyroxenite-peridotite mantle sequences from Northern Apennine ophiolites (Italy) - Abstract book - RENDICONTI ONLINE DELLA SOCIETÀ GEOLOGICA ITALIANA - n. volume 31, Suppl. 1 [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

E. Barbieri; D. Brunelli; A. Cipriani; M. Mazzucchelli ( 2014 ) - Melting of Plume Residue beneath the Afar: Implications for Axial Basalts Geochemistry - Abstract book - Socià Geolgica Italiana Roma ITA) - RENDICONTI ONLINE DELLA SOCIETÀ GEOLOGICA ITALIANA - n. volume 31, Suppl. 1 - pp. da 489 a 489 ISSN: 2035-8008 [Abstract in rivista (266) - Abstract in Rivista]
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.

Vescogni, Alessandro; Bosellini, Francesca; Cipriani, Anna; Gürler, Gonca; Ilgar, Ayhan; Paganelli, Emanuele; Chiossi, Irene . ( 2014 ) - Stratigraphy and facies analisys of the Langhian Dağpazarı reef complex (Mut Basin, Southern Turkey) - Book of Abstract of the RCMNS 2013 - Istanbul Technical University Istanbul TUR) - n. volume - - pp. da 111 a 111 ISBN: 978-975-561-438-0 ISSN: - [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

A. Vescogni; F.R. Bosellini; A. Cipriani; G. Gurler; A.Ilgar; E. Paganelli ( 2014 ) - The Dağpazarı carbonate platform (Mut Basin, Southern Turkey): facies and environmental reconstruction of a coral reef system during the Middle Miocene Climatic Optimum. - PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY - n. volume 410 - pp. da 213 a 232 ISSN: 0031-0182 [Articolo in rivista (262) - Articolo su rivista]
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.

Palmiotto, C.; Corda, L.; Cipriani, Anna; Dick, H.J.B.; Douville, E.; Gasperini, L.; Ligi, M.; Montagna, P.; Thil, F.; Bonatti, E. ( 2013 ) - Ancient and modern oceanic islands: a classification - Abstract book [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Barbieri, Emiliano; Cipriani, Anna; Brunelli, Daniele; Paganelli, Emanuele ( 2013 ) - Barbieri E, Cipriani A, Brunelli D & Paganelli E (2013) Mineralogical Magazine, 77(5) 655 - MINERALOGICAL MAGAZINE - n. volume 77(5) - pp. da 655 a 655 ISSN: 1471-8022 [Abstract in rivista (266) - Abstract in Rivista]
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.

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;Anna Cipriani;Carlos Di Bella;Ahmed H. Rabia;Alfredo Garcia;Mar’yana Vakolyuk;Kuleswar Singha;Maria E. Beget;Stefan Erasmi;Franziska Albrecht;Brian Shaw;Michael Obersteiner ( 2013 ) - Downgrading Recent Estimates of Land Available for Biofuel Production - ENVIRONMENTAL SCIENCE & TECHNOLOGY - n. volume 47 - pp. da 1688 a 1694 ISSN: 0013-936X [Articolo in rivista (262) - Articolo su rivista]
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.

Alexey Pertsev;Leonid Aranovich;Vsevolod Prokofiev;Nikolay Bortnikov;Anna Cipriani ( 2013 ) - High-Salinity Seawater-Derived Fluids and Lower-Crust Hydrothermal Mineralization at the Vema Lithospheric Section, Central Atlantic - PROCEDIA EARTH AND PLANETARY SCIENCE - n. volume 7 - pp. da 677 a 680 ISSN: 1878-5220 [Articolo in rivista (262) - Articolo su rivista]
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.

Bonatti, Enrico; Ligi, Marco; Ronca, Sara; Seyler, Monique; Bosworth, William; Cipriani, Anna ( 2013 ) - Intrusion of Oceanic-type Basaltic Melts Precedes Continental Break up in the Red Sea Rift - EGU General Assembly 2013 - EGU MUNICH DEU) - n. volume 15 - pp. da 1 a 1 ISBN: 1607-7962 ISSN: - [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Borghini, G; Rampone, E; Zanetti, A; Class, C; Cipriani, Anna; Hofmann, A; Goldstein, S; Godard, M ( 2013 ) - Meter-Scale Chemical Interaction between Pyroxenite-Derived Melts and Mantle Peridotites in the Northern Apennine Ophiolites (Italy) - MINERALOGICAL MAGAZINE - n. volume 77(5) - pp. 740 ISSN: 1471-8022 [Abstract in rivista (266) - Abstract in Rivista]
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.

G. Borghini;E. Rampone;A. Zanetti;C. Class;A. Cipriani;A. W. Hofmann;S. L. Goldstein ( 2013 ) - Meter-scale Nd isotopic heterogeneity in pyroxenite-bearing Ligurian peridotites encompasses global-scale upper mantle variability - GEOLOGY - n. volume 41 - pp. da 1055 a 1058 ISSN: 0091-7613 [Articolo in rivista (262) - Articolo su rivista]
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.

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 ( 2013 ) - Nonvolcanic tectonic islands in ancient and modern oceans - GEOCHEMISTRY, GEOPHYSICS, GEOSYSTEMS - n. volume 14 - pp. da 4698 a 4717 ISSN: 1525-2027 [Articolo in rivista (262) - Articolo su rivista]
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.

Chiara Boschi;Enrico Bonatti;Marco Ligi;Daniele Brunelli;Anna Cipriani;Luigi Dallai;Massimo D'Orazio;Gretchen L. Früh-Green;Sonia Tonarini;Jaime D. Barnes;Rosa M. Bedini ( 2013 ) - Serpentinization of mantle peridotites along an uplifted lithospheric section, Mid Atlantic Ridge at 11° N - LITHOS - n. volume 178 - pp. da 3 a 23 ISSN: 0024-4937 [Articolo in rivista (262) - Articolo su rivista]
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.

Marco Ligi; Enrico Bonatti; Giovanni Bortoluzzi; Anna Cipriani; Luca Cocchi; Fabio Caratori Tontini; Eugenio Carminati; Luisa Ottolini; Antonio Schettino ( 2012 ) - Birth of an ocean in the Red Sea: Initial pangs - GEOCHEMISTRY, GEOPHYSICS, GEOSYSTEMS - n. volume 13-8 - pp. da 1 a 29 ISSN: 1525-2027 [Articolo in rivista (262) - Articolo su rivista]
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.

Pertsev, A.; Cipriani, Anna; Aranovich, L.; Prokofiev, V. ( 2012 ) - Reducing reactions of hydrothermal front in lower-crustal magmatically active zone: an example from the Vema lithospheric section, central Atlantic - Proceedings of the 34th International Geological Congress 2012 - pp. 1401 ISSN: - [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Paganelli E.; Brunelli D.; Seyler M.; Bonatti E.; Cipriani A.; Ligi M. ( 2011 ) - Deep versus shallow melt stagnation in an ultra-slow / ultra-cold ridge segment: the Andrew Bain southern RTI (SWIR) - 2011 AGU Fall Meeting - EOS [Poster (275) - Poster]
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.

Bonatti, E.; Cipriani, Anna.; Corda, Laura; Montagna, Paolo; Palmiotto, Camilla ( 2011 ) - Foramol facies in equatorial carbonates: insight from Miocene Atlantic platforms - Abstract book [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
Abstract

Foramol facies in equatorial carbonates: insight from Miocene Atlantic platforms

M. Ligi;E. Bonatti;F. C. Tontini;A. Cipriani;L. Cocchi;A. Schettino;G. Bortoluzzi;V. Ferrante;S. Khalil;N. C. Mitchell;N. Rasul ( 2011 ) - Initial burst of oceanic crust accretion in the Red Sea due to edge-driven mantle convection - GEOLOGY - n. volume 39 - pp. da 1019 a 1022 ISSN: 0091-7613 [Articolo in rivista (262) - Articolo su rivista]
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.

Anna Cipriani; Enrico Bonatti; Richard W. Carlson ( 2011 ) - Nonchondritic 142Nd in suboceanic mantle peridotites - Geochemistry Geophysics Geosystems - GEOCHEMISTRY, GEOPHYSICS, GEOSYSTEMS - n. volume 12 - pp. da 1 a 8 ISSN: 1525-2027 [Articolo in rivista (262) - Articolo su rivista]
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.

Borghini, G; Rampone, E; Zanetti, A; Class, C; Cipriani, Anna; Hofmann, A.W.; Goldstein, S.L. ( 2011 ) - Pyroxenites in peridotites from External Liguride ophiolites (Italy): Insights on small scale heterogeneities in MORB mantle - MINERALOGICAL MAGAZINE - n. volume Vol. 75 (3) - pp. da 555 a 555 ISSN: 1471-8022 [Abstract in rivista (266) - Abstract in Rivista]
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.

Cipriani, A.; Brunelli, D.; Seyler, M.; Paganelli, E.; Barbieri, E. ( 2011 ) - REE pattern rotation in an open system melting: case studies from slow and ultraslow spreading ridges - EOS - n. volume EOS, Trans. AGU, Fall Meet. Suppl., [Abstract in rivista (266) - Abstract in Rivista]
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.

Borghini, G; Rampone, Zanetti; Cipriani, Anna; E, ; Aw, A.W.; Class, C; Hofmann, ; Goldstein, S.L. ( 2011 ) - Small scale heterogeneities in MORB mantle: Insights on pyroxenite-peridotite association from External Liguride ophiolites (Italy) - EPITOME - n. volume vol.4 - pp. da 324 a 325 ISSN: 1972-1552 [Abstract in rivista (266) - Abstract in Rivista]
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.

Rampone, E; Borghini, G; Hofmann, A.W.; Class, C; Cipriani, Anna; Zanetti, A; Goldstein, S.L. ( 2011 ) - Upper mantle isotopic heterogeneities - global overview with new results from Alpine-Apennine ophiolites - EOS - n. volume EOS, Trans. AGU, Fall Meet. Suppl., [Abstract in rivista (266) - Abstract in Rivista]
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.

Ligi, Marco; Bonatti, Enrico; Brunelli, Daniele; Cipriani, Anna; Ottolini, Luisa ( 2011 ) - Water in Mid Ocean Ridge Basalts: Some Like it Hot, Some Like it Cold [Monografia o trattato scientifico (276) - Monografia/Trattato scientifico]
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”.

E. Paganelli; D. Brunelli; M. Seyler; E. Bonatti; A. Cipriani; M. Ligi ( 2010 ) - Heterogeneous melting and refertilization of a mantle parcel in a cold spot: Andrew Bain fracure zone (SWIR) - 89th SIMP Journal of Abstracts [Poster (275) - Poster]
Abstract

abstract

Zanetti A.; Mazzucchelli M.; Hémond C.; Cipriani A.; Bertotto G.W.; Cingolani C.A.; Vannucci R. ( 2010 ) - Nd, Sr and Pb isotopic composition of metasomatised xenoliths from the backarc Patagonian MantleWedge: Insights into the origin of the uprising melts - GEOPHYSICAL RESEARCH ABSTRACTS - n. volume 12 - pp. da 13170 a 13170 ISSN: 1607-7962 [Abstract in rivista (266) - Abstract in Rivista]
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.

A. Cipriani; E. Bonatti; M. Seyler; H. Brueckner; D. Brunelli; L. Dallai; S. Hemming; M. Ligi; L. Ottolini; B. Turrin ( 2009 ) - A 19 to 17 Ma amagmatic extension event at the Mid-Atlantic Ridge: ultramafic mylonites from the Vema Lithospheric Section - GEOCHEMISTRY, GEOPHYSICS, GEOSYSTEMS - n. volume 10 - pp. da 1 a 53 ISSN: 1525-2027 [Articolo in rivista (262) - Articolo su rivista]
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.

RIVALENTI G.; MAZZUCCHELLI M.; ZANETTI A.; HÉMOND C.; CIPRIANI A. ( 2009 ) - Evidence for ultra-depleted Pb isotopic component in the backarc Patagonian mantle wedge. - GEOCHIMICA ET COSMOCHIMICA ACTA - n. volume 73, 13S [Abstract in rivista (266) - Abstract in Rivista]
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.

RIVALENTI G; MAZZUCCHELLI M; ZANETTI A; HÉMOND C; CIPRIANI A; BERTOTTO GW; CINGOLANI CA ( 2009 ) - Evidence for ultra-depleted Pb isotopic metasomatic liquid in the backarc Patagonian Mantle Wedge - EPITOME - n. volume 3 - pp. da 208 a 208 ISSN: 1972-1552 [Abstract in rivista (266) - Abstract in Rivista]
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.

D. Brunelli; E. Bonatti; A. Cipriani; M. Ligi; M. Seyler; L. Ottolini ( 2009 ) - Invited talk: Scale and nature of the mantle heterogeneities at the Vema Lithospheric Section (Mid Atlantic Ridge 11°N) - EOS Trans. AGU - AGU Washington USA) - EOS - n. volume 90(52) [Abstract in rivista (266) - Abstract in Rivista]
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.

M. Ligi; E. Bonatti; D. Brunelli; A. Cipriani ( 2009 ) - Present day versus Temporal Heterogeneity of the Subridge Mantle in the Central Atlantic - EOS - n. volume 90 - pp. da 1 a 1 ISSN: 0096-3941 [Abstract in rivista (266) - Abstract in Rivista]
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

D. Brunelli; E. Bonatti; A. Cipriani; M. Ligi; M. Seyler; L. Ottolini ( 2009 ) - Scale and nature of the mantle heterogeneities at the Vema Lithospheric Section (Mid Atlantic Ridge 11°N) - EOS - n. volume 90 - pp. da 1 a 1 ISSN: 0096-3941 [Abstract in rivista (266) - Abstract in Rivista]
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.

A. Cipriani; E. Bonatti; D. Brunelli; M. Ligi ( 2009 ) - 26 Million Years of Mantle Upwelling Below a Segment of the Mid Atlantic Ridge: the Vema Lithospheric Section Revisited - EARTH AND PLANETARY SCIENCE LETTERS - n. volume 285 - pp. da 87 a 95 ISSN: 0012-821X [Articolo in rivista (262) - Articolo su rivista]
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.

Paganelli E.; Brunelli D.; Bonatti E.; Cipriani A.; Ligi M. ( 2008 ) - Multi-stage impregnation of the lithospheric mantle at the Andrew Bain FZ (SWIR) - 2008 AGU Fall Meeting - EOS - n. volume 89(53) [Poster (275) - Poster]
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

Ligi M.; Bonatti E.; Bortoluzzi G.; Brunelli D.; Caratori Tontini F.; Cipriani A.; Cocchi L.; Cuffaro M.; Ferrante V.; Khalil S.; Mitchell N C.; Rasul N.; Schettino A. ( 2008 ) - Sea-floor spreading initiation: constraints from geophysical data of the Thetis Deep, northern Red Sea - EOS Trans. AGU - AGU Washington USA) - EOS - n. volume 89 (53) [Abstract in rivista (266) - Abstract in Rivista]
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.

Ligi Marco; Bonatti Enrico; Brunelli Daniele; Cipriani Anna ( 2007 ) - Accretion at a Mid Atlantic Ridge Segment: a 25 million years long story - VI Forum - FIST Udine ITA) - EPITOME - n. volume 2 [Abstract in rivista (266) - Abstract in Rivista]
Abstract

abs

Brunelli D; Bonatti E; Cipriani A; Grindlay N R; Ligi M; Paganelli E; Sclater J ( 2007 ) - Crust-Poor Lithosphere at Cold Spots in the Mid Atlantic and SW Indian Ridges - EOS Trans. AGU - AGU Washington USA) - EOS - n. volume 88 (52) [Abstract in rivista (266) - Abstract in Rivista]
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.

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 D.; PERTSEV A.N.; CIPRIANI A.; BORTOLUZZI G.; MERCURI R.; PAGANELLI E.; MUCCINI F.; TAKEUCHI C.; ZAFFAGNINI F.; DOBROLYUBOVA K.O.; ( 2007 ) - Investigation of the Andrew Bain transform fault zone (African-Antartctic Region) - DOKLADY EARTH SCIENCES - n. volume 416 - pp. da 991 a 998 ISSN: 1028-334X [Articolo in rivista (262) - Articolo su rivista]
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.

Kelemen P.B.; Kikawa E.; Miller D.J; Abe N.; Bach W.; Carlson R.L.; Casey J.F.; Chambers L.M.; Cheadle M.; Cipriani A.; 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; ( 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 - Proceedings of the Ocean Drilling ProgramProceedings of the Ocean Drilling Program, 209 Scientific Results - Kelemen, P.B., Kikawa, E., and Miller, D.J. (Eds.) College Station, TX USA) - n. volume 209 - pp. da 1 a 33 ISBN: 9780008845896 ISSN: - [Contributo in volume (Capitolo o Saggio) (268) - Capitolo/Saggio]
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

Cipriani A.; Ligi M; Bonatti E; Brunelli D ( 2007 ) - Solid mantle upwelling rate beneath the Mid Atlantic Ridge - EOS Trans. AGU - AGU Washington USA) - EOS - n. volume 88 (52) [Abstract in rivista (266) - Abstract in Rivista]
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.

M. Ligi; E. Bonatti; N.R. Grindlay; J. Sclater; S. Skolotnev; A. Peyve; G. Bortoluzzi; D. Brunelli; A. Cipriani; R. Mercuri; F. Muccini; E. Paganelli; 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 and L. Zotov ( 2006 ) - ANDREW BAIN TRANSFORM: MULTIPLE CONTINENTAL-TYPE TRANSFORM BOUNDARIES AT MID-OCEAN RIDGE - Polar Ridges Meeting and Workshop - pp. da 1 a 1 ISSN: - [Poster (275) - Poster]
Abstract

abstract

D. BRUNELLI; SEYLER M; CIPRIANI A; BONATTI E. AND OTTOLINI L ( 2006 ) - Discontinuous melt extraction and weak refertilization of mantle peridotites at the Vema Lithospheric Section (Mid Atlantic Ridge) - JOURNAL OF PETROLOGY - n. volume 47 - pp. da 745 a 771 ISSN: 0022-3530 [Articolo in rivista (262) - Articolo su rivista]
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.

A. Cipriani; D. Brunelli; M. Ligi; E. Bonatti ( 2006 ) - From magma-engorged to magma starved “constipated” lithosphere: The Mid Atlantic Ridge from 40°N to the Equator - Polar Ridges - INTERRIDGE Pavia ITA) - n. volume 1 - pp. da 1 a 1 ISBN: 0000000000 ISSN: - [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
Abstract

abstract

Ligi M.; Bonatti E.; Bortoluzzi G.; Brunelli D.; Carminati E.; Cipriani A.; Ferrante V.; Redini F.; Barbino G. ( 2006 ) - Initial emplacement of Oceanic Lithosphere in the northern Red Sea - EOS Trans. AGU - AGU Washington USA) - EOS - n. volume 87 (52) [Abstract in rivista (266) - Abstract in Rivista]
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.

D. Brunelli; R. Clocchiatti; A. Cipriani; M. Ligi; E. Paganelli; L. Ottolini and E. Bonatti ( 2006 ) - Snapshots fo the magma plumbing system from melt inclusions and residual peridotites of the Vema Lithospheric Section (MAR 11°N) - Polar Ridges - INTERRIDGE Pavia ITA) - n. volume 1 - pp. da 1 a 1 ISBN: 0000000000 ISSN: - [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
Abstract

abstract

E. Bonatti; G. Bortoluzzi; D. Brunelli; V. Ferrante; M. Ligi; M. Lopez Correa; F. Redini; A. Cipriani; 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 and Y.M Al-Hazmi ( 2006 ) - TRANSITION FROM A CONTINENTAL TO AN OCEANIC RIFT IN THE NORTHERN RED SEA - Polar Ridges Meeting and Workshop - pp. da 1 a 1 ISSN: - [Poster (275) - Poster]
Abstract

abstract

Cipriani A.; Bonatti E.; Brunelli D.; Ligi M. ( 2006 ) - 26 Million Years of mantle upwelling below a segment of the Mid Atlantic Ridge: the Vema Lithosperic Section revisited - EOS Trans. AGU - AGU Washington USA) - EOS - n. volume 87 (52) [Abstract in rivista (266) - Abstract in Rivista]
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.

E. BONATTI; D. BRUNELLI; W. R. BUCK; A. CIPRIANI; P. FABRETTI; V. FERRANTE; L. GASPERINI AND M. LIGI ( 2005 ) - Flexural uplift of a lithospheric slab near the Vema Transform (Central Atlantic): timing and mechanisms - EARTH AND PLANETARY SCIENCE LETTERS - n. volume 240 - pp. da 642 a 655 ISSN: 0012-821X [Articolo in rivista (262) - Articolo su rivista]
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.

Marco Ligi; Enrico Bonatti; Anna Cipriani; Luisa Ottolini ( 2005 ) - Water-rich basalts at mid-ocean-ridge cold spots - NATURE - n. volume 434 - pp. da 66 a 69 ISSN: 0028-0836 [Articolo in rivista (262) - Articolo su rivista]
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’.

Brunelli D.; M. Seyler; A. Cipriani; L. Ottolini; E. Bonatti ( 2005 ) - Weak residual mantle refertilization by partial melts beneath the Mid Atlantic Ridge - Geoitalia 5° Forum - FIST Udine ITA) - EPITOME - n. volume 1 [Abstract in rivista (266) - Abstract in Rivista]
Abstract

abstract

Brunelli D. ; M. Seyler; A. Cipriani; L. Ottolini; E. Bonatti ( 2004 ) - Discontinuous/episodic partial melt extraction from the melting region beneath the Mid Atlantic Ridge - . - Soc Fran Min Pet Paris FRA) - BULLETIN DE LIAISON DE LA SOCIÉTÉ FRANÇAISE DE MINÉRALOGIE ET DE CRISTALLOGRAPHIE - n. volume 16,3 - pp. da 1 a 1 ISSN: 0999-5870 [Abstract in rivista (266) - Abstract in Rivista]
Abstract

abstract

Ligi M.; Bonatti E.; Brunelli D.; Buck R.W.; Cipriani A. ( 2004 ) - Flexural uplift of a lithospheric slab near the Vema transform (Central Atlantic): timing and mechanism - EOS Trans. AGU - AGU Washington USA) - EOS - n. volume 85 (47) [Abstract in rivista (266) - Abstract in Rivista]
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

CIPRIANI A; BRUEKNER H; BONATTI E; D. BRUNELLI ( 2004 ) - Oceanic crust generated by elusive parents: Sr/Nd isotopes in basalt-peridotite pairs from the Mid-Atlantic Ridge - GEOLOGY - n. volume 32 - pp. da 657 a 660 ISSN: 0091-7613 [Articolo in rivista (262) - Articolo su rivista]
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.

Kelemen P.; Kikawa E.; Miller D.J.; Natsue Abe; Wolfgang Bach; Richard L. Carlson; John F. Casey; Lynne M. Chambers; Michael Cheadle; Anna Cipriani; 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. ( 2004 ) - ODP Leg 209 drills into mantle peridotite along the mid-Atlantic ridge from 14°N to 16°N - JOIDES JOURNAL - n. volume 30 - pp. da 14 a 19 ISSN: 0734-5615 [Articolo in rivista (262) - Articolo su rivista]
Abstract

not available

Kelemen P.B.; Kikawa E.; Miller D.J; Abe N.; Bach W.; Carlson R.L.; Casey J.F.; Chambers L.M.; Cheadle M.; Cipriani A.; 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.; ( 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 - Lorri L. Peters College Station, TX, United States USA) [Monografia o trattato scientifico (276) - Monografia/Trattato scientifico]
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.

Cipriani A.; Bonatti E.; Brunelli D.; Ligi M.; Ottolini L. ( 2004 ) - Small scale mantle heterogeneities sampled through oceanic basalts from ridge-transform intersections - EOS Trans. AGU - AGU Washington USA) - EOS - n. volume 85 (47) [Abstract in rivista (266) - Abstract in Rivista]
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

D. BRUNELLI; BONATTI E; CIPRIANI A; OTTOLINI L ( 2003 ) - Mantle peridotites from the Bouvet Triple Junction Region, South Atlantic. - TERRA NOVA - n. volume 15 - pp. da 194 a 203 ISSN: 0954-4879 [Articolo in rivista (262) - Articolo su rivista]
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.

BONATTI E; LIGI M; D. BRUNELLI; CIPRIANI A; FABRETTI P; FERRANTE V; GASPERINI L; OTTOLINI L ( 2003 ) - Mantle thermal pulses below the Mid-Atlantic Ridge and temporal variations in the formation of oceanic lithosphere. - NATURE - n. volume 423 - pp. da 499 a 505 ISSN: 0028-0836 [Articolo in rivista (262) - Articolo su rivista]
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

Bonatti E.; Ligi M.; Brunelli D.; Cipriani A.; Gasperini L. ( 2002 ) - Is the Mid-Atlantic Ridge becoming hotter with time? - 2002 AGU Fall Meeting - EOS - n. volume 83(47) [Poster (275) - Poster]
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.

A.A. Peyve; K.O. Dobrolhybova; V.N. Efimov; Anna Cipriani; Marco Ligi; M.; A.O. Mazarovich; A.S. Perfil'ev; Yu.N. Raznitsyn; G.N. Savel'eva; V.A. Simonov; S.G. Skolotnev ( 2001 ) - Structure peculiarities of the Sierra Leone fracture zone (central Atlantic) - DOKLADY AKADEMII NAUK. ROSSIISKAIA AKADEMIIA NAUK - n. volume 377-6 - pp. da 803 a 806 ISSN: 0869-5652 [Articolo in rivista (262) - Articolo su rivista]
Abstract

in russian

Cipriani A.; Brunelli D.; Brueckner H.K.; Bonatti E. ( 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 - 2001 AGU Fall Meeting - EOS [Poster (275) - Poster]
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.

Bonatti E.; Gasperini L.; Ligi M.; Brunelli D.; Cipriani A.; Fabretti P. ( 1999 ) - La struttura termica del mantello oceanico e la creazione della litosfera oceanica nell’Atlantico centrale e meridionale - Abstract Geoitalia - SIMP Pisa ITA) - PLINIUS - n. volume 22 - pp. da 1 a 1 ISSN: 1120-317X [Abstract in rivista (266) - Abstract in Rivista]
Abstract

abstract

Bonatti, E.; Brunelli, Daniele; Cipriani, Anna; Ottolini, L.; Seyler, M. ( 1999 ) - Spatial and temporal heterogeneity of the oceanic mantle in the Central Atlantic - Ofioliti, 24:72 - n. volume 24 - pp. 72 ISSN: - [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
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.

Brunelli D.; Cipriani A.; Ottolini L.; Vaggelli G.; Santo A.P.; Bonatti E. ( 1999 ) - The Bouvet melt anomaly in the South Atlantic: geochemistry and influence on the Triple Junction Geometry - Abstract Geoitalia - SIMP Pisa ITA) - PLINIUS - n. volume 22 - pp. da 1 a 1 ISSN: 1120-317X [Abstract in rivista (266) - Abstract in Rivista]
Abstract

abstract

Gasperini L.; Bonatti E.; Borsetti AM.; Brunelli D.; Capotondi L.; Carrara G.; Cipriani A.; Fabretti P.; Ligi M.; Kastens K. ( 1999 ) - Time constraints on the emplacement of an uplifted sliver of oceanic lithosphere at the Vema transverse ridge (Central Atlantic) - EUG 10 - EUG cambridge GBR) - JOURNAL OF CONFERENCE ABSTRACTS - n. volume 4-1 [Abstract in rivista (266) - Abstract in Rivista]
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.

Brunelli D.; Cipriani A.; Ottolini L.; Bonatti E. ( 1999 ) - Vema Fracture Zone (Central Atlantic): Temporal variations of mantle composition and of accretion processes at ridge axis - Journal of Conference Abstracts - EUG Cambridge GBR) - JOURNAL OF CONFERENCE ABSTRACTS - n. volume 4-1 [Abstract in rivista (266) - Abstract in Rivista]
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.

Ligi M.; Bonatti E.; Brueckner HK.; Brunelli D.; Cipriani A.; Fabretti P.; Ottolini L ( 1998 ) - Contrasting Ultra-Slow Ridges near the Bouvet Triple Junction in the South Atlantic - EOS Trans. AGU - AGU Washington USA) - EOS - n. volume 1 [Abstract in rivista (266) - Abstract in Rivista]
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.

Paola Fabretti; Enrico Bonatti; Alexander Peyve; Daniele Brunelli; Anna Cipriani; 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; ( 1998 ) - First results of cruise S19 (PRIMAR project): Petrological and structural investigations of the Vema transverse ridge (equatorial Atlantic) - GIORNALE DI GEOLOGIA - n. volume 60 - pp. da 3 a 16 ISSN: 0017-0291 [Articolo in rivista (262) - Articolo su rivista]
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.

Bonatti E.; Brunelli D.; Cipriani A.; Fabretti P.; Gasperini L.; Ligi M.; Peyve A.; Savelieva G.; Skolotnev S.; Susini S. ( 1998 ) - Variations with age of ultramafic composition near the Vema fracture zone, Central Atlantic - EOS Trans. AGU - AGU Washington USA) - EOS - n. volume 1 [Abstract in rivista (266) - Abstract in Rivista]
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.

Ligi M.; Bonatti E.; Bortoluzzi G.; Carrara G.; Fabretti P.; Penitenti D.; Terenzoni M.; Brunelli D.; Cipriani A.; Gilod D.; Peyve A.A.; Skolotnev S.; Turko N. ( 1997 ) - Death and transfiguration of a triple junction in the south Atlantic - Geophysical Newsletter XXII EGS General Assembly [Poster (275) - Poster]
Abstract

abstract

Bonatti E.; Gasperini L.; Ligi M.; Carrara G.; Chierici F.; Fabretti P.; Susini S.; Tartarotti P.; Brunelli D.; Cipriani A.; Gilod D.; Peyve A.A.; Skolotnev S.; Turko N. ( 1997 ) - Morphostructural analysis of the western intersection of the mid Atlantic ridge with the Romanche transform (equatorial Atlantic) - Geophysical Newsletter XXII EGS General Assembly [Poster (275) - Poster]
Abstract

abstract

Luca Gasperini; Enrico Bonatti; Daniele Brunelli; Gabriela Carrara; Anna Cipriani; Paola Fabretti; Dolores Gilod; Marco Ligi; Alexander Peyve; Sergey Skolotnev; Sara Susini; Paola Tartarotti; Natasha Turko; ( 1997 ) - New data on the geology of the Romanche F.Z., equatorial Atlantic: PRIMAR-96 cruise report - GIORNALE DI GEOLOGIA - n. volume 59 - pp. da 3 a 18 ISSN: 0017-0291 [Articolo in rivista (262) - Articolo su rivista]
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.

Gabriela Carrara; Giovanni Bortoluzzi; Nevio Zitellini; Enrico Bonatti; Daniele Brunelli; Anna Cipriani; Paola Fabretti; Luca Gasperini; Marco Ligi; Daniela Penitenti; P.F. Sciuto; A. Mazarovich; A. Peyve; N. Turko; S. Skolotnev; D. Gilod ( 1997 ) - The Bouvet Triple Junction Region (south Atlantic): A report on two geological expeditions - GIORNALE DI GEOLOGIA - n. volume 59 - pp. da 19 a 33 ISSN: 0017-0291 [Articolo in rivista (262) - Articolo su rivista]
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.