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Francesca REMITTI
Professore Associato
Dipartimento di Scienze Chimiche e Geologiche - Sede Dipartimento di Scienze Chimiche e Geologiche
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Pubblicazioni
2023
- Heterogeneity‐driven localization and weakening in scaly clays from a fossil accretionary prism
[Articolo su rivista]
Aretusini, S.; Mittempergher, S.; Remitti, F.; Arletti, R.; Polisi, M.; De Paola, N.; Tesei, T.
abstract
2023
- Internal architecture of the frontal part of subduction accretionary prism: the role of folding in brittle diffuse deformation
[Abstract in Atti di Convegno]
Remitti, F.; Festa, A.; Nirta, G.; Barbero, E.; Mittempergher, S.
abstract
2022
- Mélanges and chaotic rock units: Implications for exhumed subduction complexes and orogenic belts
[Articolo su rivista]
Festa, Andrea; Barbero, Edoardo; Remitti, Francesca; Ogata, Kei; Pini, Gian Andrea
abstract
2021
- Mechanical behavior of the shallow part of megathrusts: hints from the Sestola Vidiciatico tectonic Unit (Northern Apennines, Italy)
[Abstract in Atti di Convegno]
Remitti, F.; Mittempergher, S.; Festa, A.; Cipriani, A.; Lugli, F.
abstract
2020
- Cyclical variations of fluid sources and stress state in a shallow megathrust zone mélange
[Articolo su rivista]
Cerchiari, Anna; Remitti, Francesca; Mittempergher, Silvia; Festa, Andrea; Lugli, Federico; Cipriani, Anna
abstract
Differences in REE patterns of calcite from extensional and shear veins of the Sestola Vidiciatico Tectonic Unit in Northern Apennines suggest variations in fluid source during the seismic cycle in an ancient analogue of a shallow megathrust (Tmax ̴100°-150°C). In shear veins, a positive Eu anomaly suggests an exotic fluid source, likely hotter than the fault environment. Small-scale extensional veins were derived instead from a local fluid in equilibrium with the fault zone rocks. Mutually crosscutting relations between two sets of extensional veins, parallel and perpendicular to the megathrust, suggest a repeated shifting of the σ1 and σ3 stresses during the seismic cycle. This is consistent with: (i) a seismic phase, with brittle failure along the thrust, crystallization of shear veins from an exotic fluid, stress drop and stress rotation; (ii) a post-seismic phase, with fault-normal compaction and formation of fault-normal extensional veins fed by local fluids; (iii) a reloading phase, where shear stress and pore pressure are gradually restored and fault-parallel extensional veins form, until the thrust fails again. The combination of geochemical and structural analyses in veins from exhumed megathrust analogues represents a promising tool to better understand the interplay between stress state and fluids in modern subduction zones.
2020
- Geology of the High Sillaro Valley (Northern Apennines of Italy)
[Articolo su rivista]
Panini, Filippo; Bettelli, Giuseppe; Carlini, Mirko; Fioroni, Chiara; Nirta, Giuseppe; Remitti, Francesca
abstract
2020
- Structural constraints on the subduction of mass transport deposits in convergent margins
[Capitolo/Saggio]
Geersen, Jacob; Festa, Andrea; Remitti, Francesca
abstract
2020
- The State of Stress on the Fault Before, During, and After a Major Earthquake
[Articolo su rivista]
Brodsky, Emily E.; Mori, James J.; Anderson, Louise; Chester, Frederick M.; Conin, Marianne; Dunham, Eric M.; Eguchi, Nobu; Fulton, Patrick M.; Hino, Ryota; Hirose, Takehiro; Ikari, Matt J.; Ishikawa, Tsuyoshi; Jeppson, Tamara; Kano, Yasuyuki; Kirkpatrick, James; Kodaira, Shuichi; Lin, Weiren; Nakamura, Yasuyuki; Rabinowitz, Hannah S.; Regalla, Christine; Remitti, Francesca; Rowe, Christie; Saffer, Demian M.; Saito, Saneatsu; Sample, James; Sanada, Yoshinori; Savage, Heather M.; Sun, Tianhaozhe; Toczko, Sean; Ujiie, Kohtaro; Wolfson-Schwehr, Monica; Yang, Tao
abstract
2018
- Does subduction of mass transport deposits (MTDs) control seismic behavior of shallow–level megathrusts at convergent margins?
[Articolo su rivista]
Festa, Andrea; Dilek, Yildirim; Mittempergher, Silvia; Ogata, Kei; Pini, Gian Andrea; Remitti, Francesca
abstract
We present a critical appraisal of the role of subducted, medium (10–1000 km2) to giant (≥1000 km2) and heterogeneous, mud-rich mass transport deposits (MTDs) in seismic behavior and mechanisms of shallow earthquakes along subduction plate interfaces (or subduction channels) at convergent margins. Our observations from exhumed ancient subduction complexes around the world show that incorporation of mud-rich MTDs with a “chaotic” internal fabric (i.e., sedimentary mélanges or olistostromes) into subduction zones strongly modifies the structural architecture of a subduction plate interface and the physical properties of subducted material. The size and distribution of subducted MTDs with respect to the thickness of a subduction plate interface are critical factors influencing seismic behavior at convergent margins. Heterogeneous fabric and compositions of subducted MTDs may diminish the effectiveness of seismic ruptures considerably through the redistribution of overpressured fluids and accumulated strain. This phenomenon possibly favors the slow end-member of the spectrum of fault slip behavior (e.g., Slow Slip Events, Very Low Frequency Earthquakes, Non-Volcanic Tremors, creeping) compared to regular earthquakes, particularly in the shallow parts (T < 250 °C) of a subduction plate interface.
2018
- Fluid-related deformation processes at the up- and downdip limits of the subduction thrust seismogenic zone: What do the rocks tell us?
[Capitolo/Saggio]
Fagereng, Å; Diener, J. F. A.; Ellis, S.; Remitti, F.
abstract
The subduction thrust interface represents a zone of concentrated deformation coupled to fluid generation, flow, and escape. Here, we review the internal structure of the megathrust as exposed in exhumed accretionary complexes, and we identify a deformation sequence that develops as material entering the trench is subducted through the seismogenic zone. Initial ductile flow in soft sediment generates dismembered, folded, and boudinaged bedding that is crosscut by later brittle discontinuities. Veins formed along early faults, and filling hydrofractures with the same extension directions as boudins in bedding, attest to fluid-assisted mass transfer during the shallow transition from ductile flow to brittle deformation. In higher-metamorphic-grade rocks, veins crosscut foliations defined by mineral assemblages stable at temperatures beyond those at the base of the seismogenic zone. The veins are, however, themselves ductilely deformed by diffusion and/or dislocation creep, and thus they record fracture and fluid flow at a deeper brittle-to-ductile transition. The results of numerical models and mineral equilibria modeling show that compaction of pore spaces may occur over a wide zone, as underconsolidated sediments carry water under the accretionary prism to the region where the last smectite breaks down at a temperature of ≤150 °C. However, at temperatures above clay stability, no large fluid release occurs until temperatures reach the zone where lawsonite and, subsequently, chlorite break down, i.e., generally in excess of 300 °C. In thermal models and strength calculations along overpressured subduction interfaces, where phyllosilicates form an interconnected network that controls rheology, as is generally observed, the deep brittle-viscous transition—analogous to the base of the seismogenic zone—occurs at temperatures less than 300 °C. We therefore suggest that the seismogenic zone does not produce fluids in significant volumes; however, major fluid release occurs at or near the base of the seismogenic zone. These deep fluids are either trapped, thus enabling embrittlement and features such as episodic tremor and slow slip, or flow updip along a permeable interface. Overall, we highlight fluid production as spatially intermittent, but fluid distribution as controlled also by the permeability of a deforming zone, where secondary porosity is both generated and destroyed, commonly in sync with the generation and movement of fluids.
2018
- From soft sediment deformation to fluid assisted faulting in the shallow part of a subduction megathrust analogue: the Sestola Vidiciatico tectonic Unit (Northern Apennines, Italy)
[Articolo su rivista]
Mittempergher, Silvia; Cerchiari, Anna; Remitti, Francesca; Festa, Andrea
abstract
The Sestola Vidiciatico tectonic Unit (SVU) accommodated the early Miocene convergence between the subducting Adriatic plate and the overriding Ligurian prism, and has been interpreted as a field analogue for the shallow portion of subduction megathrusts. The SVU incorporated sediments shortly after their deposition and was active down to burial depth corresponding to temperatures around 150 °C. Here, we describe the internal architecture of the basal thrust fault of the SVU through a multi-scale structural analysis and investigate the evolution of the deformation mechanisms with increasing burial depth. At shallow depth, the thrust developed in poorly lithified sediments which deformed by particulate flow. With increasing depth and lithification of sediments, deformation was accommodated in a meter scale, heterogeneous fault zone, including multiple strands of crack-and-seal shear veins, associated with minor distributed shearing in clay-rich domains and pressure solution. In the last stage, slip localized along a sharp, 20 cm thick shear vein, deactivating the fault zone towards the footwall. The widespread formation of crack-and-seal shear veins since the first stages of lithification indicates that failure along the thrust occurred at high fluid pressure and low differential stress already at shallow depth. Progressive shear localization occurs in the last phases of deformation, at temperatures typical of the transition to the seismogenic zone in active megathrusts.
2017
- Miocene phosphatic hardgrounds of the Mediterranean and their biotic assemblage: new insights from the "Aturia level" of the Salento Peninsula (S. Italy)
[Abstract in Atti di Convegno]
Vescogni, Alessandro; Bosellini, Francesca Romana; Vertino, Agostina; Harzhauser, Mathias; Mandic, Oleg; Cipriani, Anna; Conti, Stefano; Remitti, Francesca
abstract
From the late Oligocene to the late Miocene, the central Mediterranean area was interested by an
extensive deposition of phosphate-rich sediments. They are usually represented by 10-20 cm thick,
sub-horizontal hardgrounds, made of phosphatic sediments arranged into thin layers separated by
erosion surfaces. Macrofossils are very abundant, their assemblage composed of colonial and solitary
corals, molluscs, echinoderms, brachiopods, bryozoans and fish teeth.
In the past decades, the Mediterranean phosphatic deposits have been the subject of several studies,
mainly aimed to understand their depositional processes and the mechanisms leading to
phosphogenesis. In particular, the formation of these sediments has been recently interpreted as
associated to the occurrence of a complex system of upwelling currents, flowing into the central
Mediterranean from the deeper, eastern region of the basin. However, most of the contributions
mainly relies on stratigraphic, sedimentary and geochemical features, whereas the macrofossil
assemblage, despite its abundance and diversity, has never been analyzed in detail. The main goal of
this study is thus a thorough investigation, mainly from a palaeontological/palaeoecological
perspective, of the phosphatic deposits of the Salento Peninsula (named “Aturia” level). Special
attention is given to the coral and mollusc associations, particularly sensitive to changes in the main
environmental stressors and representing the most abundant biotic components of the phosphatic
deposits.
The Salento Aturia level is up to 25 cm in thickness and made of several phosphatic layers separated
by erosion surfaces. Microstratigraphic and microfacies analyses allow to identify two distinct facies.
A coral rudstone, about 7-10 cm thick, constitutes the base of the hardground, while on the top lies a
detrital rudstone, made of the succession of thinner layers mainly composed of phosphatic fragments.
Most of the macrofossils are concentrated within the coral rudstone and particularly abundant are
corals, associated to molluscs and to a lesser amount to brachiopods, echinoderms, bryozoans,
serpulids and fish teeth.
The coral assemblage is composed at least by 16 taxa belonging to 4 families, represented in order of
2015
- Deformation structures in the frontal prism near the Japan Trench: Insights from sandbox models
[Articolo su rivista]
Bose, Santanu; Saha, Puspendu; Mori, James J.; Rowe, Christie; Ujiie, Kohtaro; Chester, Frederick M.; Conin, Marianne; Regalla, Christine; Kameda, Jun; Toy, Virginia; Kirkpatrick, James; Remitti, Francesca; Moore, J. Casey; Wolfson Schwehr, Monica; Nakamura, Yasuyuki; Gupta, Anchit
abstract
We have used sandbox experiments to explore the mechanics of the frontal prism structures documented by seismic reflection data and new borehole from IODP Expedition 343 (JFAST). This study investigated the effects of down-dip (normal to trench axis) variations in frictional resistance along a decollement on the structural development of the frontal wedges near subduction zones. Interpretation of seismic reflection images indicates that the wedge has been effected by trench-parallel horst-and-graben structures in the subducting plate. We performed sandbox experiments with down-dip patches of relatively high and low friction on the basal decollement to simulate the effect of variable coupling over subducting oceanic plate topography. Our experiments verify that high frictional resistance on the basal fault can produce the internal deformation and fault-and-fold structures observed in the frontal wedge by the JFAST expedition. Subduction of patches of varying friction caused a temporal change in the style of internal deformation within the wedge and gave rise to two distinctive structural domains, separated by a break in the surface slope of the wedge: (i) complexly deformed inner wedge with steep surface slope and (ii) shallow taper outer wedge, with a sequence of imbricate thrusts. Our experiments further demonstrate that the topographic slope-break in the wedge develops when the hinterland part of the wedge essentially stops deforming internally, leading to in-sequence thrusting with the formation of an outer wedge with low taper angle. For a series of alternate high and low frictional conditions on the basal fault the slope of the wedge varies temporally between a topographic slope-break and uniformly sloping wedge. (C) 2015 Elsevier Ltd. All rights reserved.
2015
- Frictional properties of fault zone gouges from the J-FAST drilling project (Mw9.0 2011 Tohoku-Oki earthquake)
[Articolo su rivista]
Remitti, Francesca; Smith, S. A. F.; Mittempergher, Silvia; Gualtieri, Alessandro; Di Toro, G.
abstract
Smectite-rich fault gouges recovered during Integrated Ocean Drilling Program Expedition 343 (Japan Trench Fast Drilling Project (J-FAST)) from the plate boundary slip zone of the 2011 Mw 9.0 Tohoku-Oki earthquake were deformed at slip velocities of 10 µm s−1 to 3.5 m s−1 and normal stresses up to 12 MPa. Water-dampened gouges (1) are weaker (apparent friction coefficient, μ* <0.1) than room-humidity gouges (apparent friction coefficient, μ* ~0.1–0.35) at all slip velocities, (2) are velocity insensitive to velocity weakening at all slip velocities, unlike room-humidity gouges that are velocity strengthening at intermediate velocities (V = 0.001–0.1 m s−1), and (3) have negligible peak μ* at high slip velocities (V > 0.1 m s−1). A significant amount of amorphous material formed in room-humidity experiments at low- and high-slip velocities, likely by comminution and disordering of smectite. Our results indicate that the frictional properties of water-dampened gouges could have facilitated propagation of the Tohoku-oki rupture to the trench and large coseismic slip at shallow depths.
2015
- Structure and lithology of the Japan Trench subduction plate boundary fault
[Articolo su rivista]
Kirkpatrick, James D.; Rowe, Christie D.; Ujiie, Kohtaro; Moore, J. Casey; Regalla, Christine; Remitti, Francesca; Toy, Virginia; Wolfson Schwehr, Monica; Kameda, Jun; Bose, Santanu; Chester, Frederick M.
abstract
The 2011 Mw9.0 Tohoku-oki earthquake ruptured to the trench with maximum coseismic slip located on the shallow portion of the plate boundary fault. To investigate the conditions and physical processes that promoted slip to the trench, Integrated Ocean Drilling Program Expedition 343/343T sailed 1 year after the earthquake and drilled into the plate boundary ∼7 km landward of the trench, in the region of maximum slip. Core analyses show that the plate boundary décollement is localized onto an interval of smectite-rich, pelagic clay. Subsidiary structures are present in both the upper and lower plates, which define a fault zone ∼5–15m thick. Fault rocks recovered from within the clay-rich interval contain a pervasive scaly fabric defined by anastomosing, polished, and lineated surfaces with two predominant orientations. The scaly fabric is crosscut in several places by discrete contacts across which the scaly fabric is truncated and rotated, or different rocks are juxtaposed. These contacts are inferred to be faults. The plate boundary décollement therefore contains structures resulting from both distributed and localized deformation. We infer that the formation of both of these types of structures is controlled by the frictional properties of the clay: the distributed scaly fabric formed at low strain rates associated with velocity-strengthening frictional behavior, and the localized faults formed at high strain rates characterized by velocity-weakening behavior. The presence of multiple discrete faults resulting from seismic slip within the décollement suggests that rupture to the trench may be characteristic of this margin.
2014
- Frictional properties of fault rocks along the shallow part of the JapanTrench décollement: insights from samples recovered during the Integrated Ocean Drilling Project Expedition 343 (the JFAST project).
[Abstract in Rivista]
Remitti, Francesca; Smith, S.; Gualtieri, Alessandro; Di Toro, G.; Nielsen, S.
abstract
-
2014
- Internal structure of the shallow plate boundary slip zone for the 2011 Tohoku-Oki Earthquake sampled during the Japan Trench Fast Drilling Project (JFAST)
[Abstract in Rivista]
Remitti, Francesca; Kirkpatrick, J.; Ujiie, K.; Mishima, T.; Chester, F.; Rowe, C.; Regalla, C.; Moore, C.; Toy, V.; Kameda, J.; Bose, S.; Wolfson Schwehr, M.
abstract
The Mw=9 2011 Tohoku-oki earthquake ruptured to the Japan Trench, with largest coseismic slip (c. 50 m) unexpectedly occurring on the shallow part of the décollement. The JFAST Project, Integrated Ocean Drilling Program (IODP) Expedition 343/343T, successfully located and sampled the shallow part of the subduction thrust shear zone (Chester et al. 2013a,b). Temperature data from a downhole observatory confirm that a thin and weak clay rich layer, identified in logging-while-drilling data and core-sample observations, is the plate boundary fault that accommodated the large slip of the earthquake rupture, as well as most of the kilometres interplate motion at the drill site (Chester et al. 2013b; Fulton et al. 2013; Lin et al. 2013; Ujiie et al. 2013). The décollement separates folded and faulted frontal prism sediments in the overriding plate from incoming flat-lying sediments along the top of the subducting plate (Chester et al., 2013b). Observed stratigraphic discontinuities at the boundary and inside the recovered fault material (Chester et al. 2013a) suggest that it contains multiple slip surfaces, many of them probably not recovered. Core analysis shows that the décollement is localized upon a strongly deformed 5≤m thick layer of smectite-rich clay, likely derived from the Paleogene to middle Miocene Pacific Plate pelagic sediments. A pervasive scaly fabric, defined by polished lustrous
surfaces, commonly striated, enclosing lenses of less fissile material (phacoids), which are self-similar at scales ranging from a few micrometers to centimeters, is distributed throughout the clay. The spacing of the surfaces increase from millimeter scale near the top of the recovered core to centimetre scale, toward the lower tectonic contact, reflecting a decrease in the magnitude of shear strain. In the upper highly sheared section, one extremely narrow discontinuity,
crosscuts this fabric, truncating without deflection the foliations that are not parallel across the contact. While the scaly fabric is indicative of distributed shear across the recovered interval (~1 m) the sharp discontinuity, resulted from localized deformation and similar to those observed at coseismic slip rates in friction experiments, could record seismic slip although not necessarily that of the Tohoku-Oki earthquake
2014
- Reconciling the Geology of the Emilia Apennines and Tuscany across the Livorno-Sillaro Lineament, northern Apennines, Italy.
[Poster]
Bettelli, Giuseppe; Panini, Filippo; Remitti, Francesca; Vannucchi, Paola
abstract
Surface expression of lithospheric faults may vary greatly as they can develop a wide range of geomorphic/topographic features and various kinds of superficial geological/structural mismatchings. The “Livorno-Sillaro Lineament” (Nirta et alii, 2007; Pascucci et alii, 2007; Bettelli et alii, 2012) is one of the most important transverse lineaments of the Northern Apennine orogen. The lithospheric-scale role of this structure has been recognized long time ago by various authors on the base of different geophysical, geological and geomorphic data, although its origin is still not well defined. Also the exact surface characters of this structure are still not well-defined, we think because they are mainly based on old and out-of-date geological data.
We present a review of the more recent stratigraphical and structural data related to the geology across the “Sillaro Lineament”, SL, the northeasternmost segment of the “Livorno-Sillaro Lineament”. Based on a re-examination and reinterpretation of the existing information about the regional geology of the Northern Apennines we conclude that the supposed mismatching of the Ligurian/Subligurian Units on the two sides of this lineament is mainly due to a lack of knowledge and to an inadequate correlation between corresponding units. Nevertheless, we recognize that this structure (along with the Secchia transverse lineament) greatly influenced the growth and the evolution of the oceanic accretionary prism/Ligurian/Subligurian thrust-nappe from the late Eocene to the late Serravallian, and also later on. In particular, we point out that at least the easternmost segment of this structure not only played an important role on the differential growth of the Ligurian/Subligurian accretionary prism-thrust nappe, but that it was responsible for the different amount of translation of the Ligurian Units on both side of the lineament.
Our conclusions and interpretations include:
1) the Sillano/Mt Morello succession, typically cropping out SE of the SL in eastern Tuscany, represents the source rocks of the Ligurian blocks forming the Sestola-Vidiciatico tectonic unit and similar units (e.g., Coscogno-Montepastore tectonic unit: Remitti et alii, 2013) cropping out NW of the SL and along the SL itself;
2) the External Ligurian unit variously named as Samoggia/Val Sillaro/Val Marecchia Varicoloured Shales, AVS, and the overlying lower to middle Eocene turbidites (e.g., Savigno Fm) cropping out in the Emilia Apennines - i.e., NW of the SL – represents a lateral and more internal equivalent of the Sillano/Mt Morello succession. The AVS were extensively present also SE of the SL, as testified by the large klippen in the Romagna Apennines (Savio and Marecchia valleys) and many small klippens in the Umbria area (Umbertide-Gubbio area);
3) along and SE of the SL the AVS form the stratigraphic base of the Mt Morello Fm. Therefore, also this unit is present on both sides of the SL;
4) the pre-middle Eocene Subligurian Units cropping out NW of the SL (Argille e Calcari di Canetolo Fm and Calcari del Groppo del Vescovo Fm) do not correspond to the so called Subligurian Units cropping out SE of the SL (i.e., in Tuscany). The latter are the result of the sedimentation in a particular paleogeographic domain, transitional to the Tuscan domain, absent or not preserved NW of the SL. This seems to represent the only real difference in the geology of the Ligurian/Subligurian thrust nappes NW and SE of the SL.
All the available data show that until the late Serravallian the thrust front of the Ligurian nappe was located in the same position across the SL. However, starting from the early-late Tortonian a differential translation of the Ligurian nappe NW of the SL took place, progressively reaching the present day position. With the exception of the Marecchia area, in the Romagna and Umbria Apennines (SE of the SL), instead, the thrust front of the Ligurian na
2013
- Early exhumation of underthrust units near the toe of an ancient erosive
subduction zone: A case study from the Northern Apennines of Italy
[Articolo su rivista]
Remitti, Francesca; Balestrieri, M. L.; Vannucchi, P.; Bettelli, Giuseppe
abstract
Apatite fission-track (AFT) analyses were performed on 16 sandstone samples from a tectonic mélange unit exposed in three tectonic windows located near the inferred front of the early Miocene subduction system of the Northern Apennines of Italy. The tectonic windows display a block-on-block tectonic mélange present under the Ligurian Units. The mélange is formed by portions of the upper plate incorporated in the plate
boundary shear zone as a consequence of a mechanism of frontal tectonic erosion during the Aquitanian (early Miocene). AFT and structural data, together with stratigraphic constraints, allow the reconstruction of a
complete deformation cycle with a phase of underthrusting followed by underplating and early exhumation of the tectonic mélange.
The exhumation, in particular, took place at ~10–20 km from the original subduction front. Moreover, the analysis suggests that
multiple faults were active at the same time in the frontal part of the subduction zone.
2013
- New insights into the late Miocene extent of the Ligurian nappe on the Adriatic side of the Northern Apennines, SE of the Sillaro Line, Italy
[Abstract in Atti di Convegno]
Bettelli, Giuseppe; Panini, Filippo; Remitti, Francesca; Vannucchi, Paola
abstract
On the Adriatic side of the Northern Apennines, SE of the Sillaro Line, both the original extent/areal distribution and the stratigraphic composition of the Ligurian thrust-nappe are still unknown and represent a highly debated topic. Few contraints have been proposed in recent papers.
Based on the presence of “Ligurian olistostromes” within the Tortonian Marnoso arenacea Fm and their absence, instead, within younger deposits, some workers have been suggested that to SE of the Sillaro Line (i.e., in the Romagna and Umbria Apennines) the Ligurian nappe was located in a more internal position. However, other workers claimed for a Ligurian thrust-sheet up to 5 km thick, partially or completely covering the internal Marnoso arenacea Fm of the Romagna Apennines. The latter hypothesis was based either on vitrinite reflectance data and apatite fission tracks data or on the composition of the Quaternary fluvial terraced deposits cropping out along the Romagna foothills. Following this latter hypothesis, the complete disappearance of the Ligurian nappe between the Sillaro Line and the Marecchia area, was the result of a differential widespread event of tectonic uplift since the Pliocene times enhancing subaerial erosion.
Here we show that a re-examination and reinterpretation of the existing knowledge about the regional geology of the Northern Apennines is essential to solve this problem. In fact, in the External Ligurian Units cropping out in the south-eastern sector of the Emilia Apennines and in the Romagna Apennines (between the Enza and the Marecchia valleys) a particular distinct unit, variously named as Val Samoggia, Val Sillaro or Val Marecchia Varicoloured Shales - AVS - have been recently distinguished from the rest of the Ligurian Units.
The AVS typically consist of green, black, red and grey shales with interbedded layers of predominantly limestones, marlstones, sandstones and manganese-rich thin layers ranging in age from the Early Cretaceous and the early Eocene. The AVS are stratigraphically inchoerent and pervasively deformed at all scales of observation, showing the typical characters of dismembered and broken formations. The AVS form the stratigraphic base of different early-middle Eocene flysches of the External Ligurian Units (i.e., Sporno, Savigno and M. Morello formations) and they share the same lithological, stratigraphical and structural character independent of the overlying formation.
Interestingly, the AVS crop out also either in few scattered outcrops (klippens) in eastern Tuscany (Casentino and Pieve Santo Stefano areas) and Umbria (between Umbertide and Nocera Umbra) where they have been interpreted not as klippens but as “olistostromes” within the Marnoso arenacea Fm. In both latter areas the AVS are unconformably overlain by few scattered remnants of the late Oligocene to middle Miocene epi-Ligurian Antognola, Monte Fumaiolo or S. Marino formations.
These data clearly imply that in the whole Romagna and Umbria Apennines on the internal Marnoso arenacea Fm a thin thrust sheet of Ligurian rocks exclusively formed of AVS and an uncomplete overlying epi-Ligurian succession, similar to that cropping out in the Val Marecchia area, was present at least up to the middle Miocene. Therefore, it follows that the thickness of the Ligurian nappe was not the same across the Sillaro Line, and that the thrust-front of the nappe to NW and SE of this tectonic lineament clearly had a quite different evolution.
These findings again show that in the Northern Apennines the Sillaro Line played also an important role inside the evolution of the Ligurian nappe.
KEY WORDS: Ligurian Units, Ligurian nappe, Northern Apennines, Romagna Apennines, Sillaro Line, Umbria Apennines, Varicoloured shales.
2013
- Stress State in the Largest Displacement Area of the 2011 Tohoku-Oki Earthquake
[Articolo su rivista]
W., Lin; M., Conin; J. C., Moore; F. M., Chester; Y., Nakamura; J. J., Mori; L., Anderson; E. E., Brodsky; N., Eguchi; B., Cook; T., Jeppson; M., Wolfson Schwehr; Y., Sanada; S., Saito; Y., Kido; T., Hirose; J. H., Behrmann; M., Ikari; K., Ujiie; C., Rowe; J., Kirkpatrick; S., Bose; C., Regalla; REMITTI, Francesca; V., Toy; P., Fulton; T., Mishima; T., Yang; T., Sun; T., Ishikawa; J., Sample; K., Takai; J., Kameda; S., Toczko; L., Maeda; S., Kodaira; R., Hino; D., Saffer
abstract
The 2011 moment magnitude 9.0 Tohoku-Oki earthquake produced a maximum coseismic slip of more than 50 meters near the Japan trench, which could result in a completely reduced stress state in the region. We tested this hypothesis by determining the in situ stress state of the frontal prism from boreholes drilled by the Integrated Ocean Drilling Program approximately 1 year after the earthquake and by inferring the pre-earthquake stress state. On the basis of the horizontal stress orientations and magnitudes estimated from borehole breakouts and the increase in coseismic displacement during propagation of the rupture to the trench axis, in situ horizontal stress decreased during the earthquake. The stress change suggests an active slip of the frontal plate interface, which is consistent with coseismic fault weakening and a nearly total stress drop.
2013
- Structure and Composition of the Plate-Boundary Slip Zone for the 2011 Tohoku-Oki Earthquake
[Articolo su rivista]
F. M., Chester; C., Rowe; K., Ujiie; J., Kirkpatrick; C., Regalla; Remitti, Francesca; J. C., Moore; V., Toy; M., Wolfson Schwehr; S., Bose; J., Kameda; J. J., Mori; E. E., Brodsky; N., Eguchi; S., Toczko
abstract
The mechanics of great subduction earthquakes are influenced by the frictional properties, structure, and composition of the plate-boundary fault. We present observations of the structure and composition of
the shallow source fault of the 2011 Tohoku-Oki earthquake and tsunami from boreholes drilled by the Integrated Ocean Drilling Program Expedition 343 and 343T. Logging-while-drilling and core-sample
observations show a single major plate-boundary fault accommodated the large slip of the Tohoku-Oki earthquake rupture, as well as nearly all the cumulative interplate motion at the drill site. The localization of
deformation onto a limited thickness (less than 5 meters) of pelagic clay is the defining characteristic of the shallow earthquake fault, suggesting that the pelagic clay may be a regionally important control on
tsunamigenic earthquakes.
2013
- Structure and composition of the plate boundary decollement in the area of maximum slip during the 2011 Tohoku-Oki earthquake
[Abstract in Atti di Convegno]
J., Kirkpatrick; C., Rowe; K., Ujiie; C., Regalla; Remitti, Francesca; V., Toy; M., Wolfson Schwehr; S., Bose; J., Kameda; J. C., Moore; F. M., Chester; 343 scientist, E. x. p.
abstract
-
2013
- The thickness of plate boundary thrust faults: implications for
Deformation mechanism and the rock record of subduction
[Abstract in Atti di Convegno]
C., Rowe; C., Moore; Remitti, Francesca; 343 Science Party, E. x. p.
abstract
-
2013
- The thickness of subduction plate boundary faults from the seafloor into the seismogenic zone
[Articolo su rivista]
C. D., Rowe; J. C., Moore; Remitti, Francesca
abstract
The thickness of an active plate boundary fault is an important parameter for understanding the strength and spatial heterogeneity of fault behavior. We have compiled direct measurements of the thickness of subduction thrust faults from active and ancient examples observed by ocean drilling and field studies in accretionary wedges. We describe a general geometric model for subduction thrust décollements, which includes multiple simultaneously active, anastomosing fault strands tens of meters thick. The total thickness encompassing all simultaneously active strands increases to ~100-350 m at ~1-2 km below seafloor, and this thickness is maintained down to a depth of ~15 km. Thin sharp faults representing earthquake slip surfaces or other discrete slip events are found within and along the edges of the tens-ofmeters-thick fault strands. Although flattening, primary inherited chaotic fabrics, and fault migration through subducting sediments or the frontal prism may build mélange sections that are much thicker (to several kilometers), this thickness does not describe the active fault at any depth. These observations suggest that models should treat the subduction thrust plate boundary fault as <1-20 cm thick during earthquakes, with a concentration of postseismic and interseismic creep in single to several strands 5-35 m thick, with lesser distributed interseismic deformation in stratally disrupted rocks surrounding the fault strands. © 2013 Geological Society of America.
2012
- Deformation, fluid flow, and mass transfer in the forearc of convergent margins: A two-day field trip in an ancient and exhumed erosive convergent margin in the Northern ApenninesDeformation, Fluid Flow, and Mass Transfer in the Forearc of Convergent Margins: Field Guides to the Northern Apennines in Emilia and in the Apuan Alps (Italy)
[Capitolo/Saggio]
Remitti, Francesca; Bettelli, Giuseppe; Panini, Filippo; Mirko, Carlini; Paola, Vannucchi
abstract
This guide provides background information and an itinerary for a two-day field trip in the Northern Apennines leaving from Modena and ending at Riolunato (Modena). The proposed field trip route leads through the Po Valley side of the Northern Apennines, in the Emilia region. The field trip provides opportunities to examine the exposed geological features related to a phase of early-middle Miocene convergence between the European and Adria plates. In particular, outcrops have been selected that exhibit features characterizing deformation in an exhumed plate boundary shear zone, interpreted as an erosive plate boundary shear zone. The sedimentary evolution and deformation of the upper and lower plates are also highlighted.
2012
- Finding Faults: Tohoku and other Active Megathrusts/Megasplays
[Abstract in Rivista]
J. C., Moore; M., Conin; B. J., Cook; J. D., Kirkpatrick; Remitti, Francesca; F., Chester; Y., Nakamura; W., Lin; S., Saito; 343 Scientific Team, E. x. p.
abstract
-
2012
- Incremental Slip Along Dilatant Faults in Ancient Fluid-Rich Subduction Zones
[Abstract in Rivista]
Remitti, Francesca; A., Fagereng; R. H., Sibson; P., Vannucchi; Bettelli, Giuseppe
abstract
-
2012
- Inherited structures and lateral variability along a plate boundary shear zone in a convergent margin: The Sestola-Vidiciatico Tectonic Unit and the Subligurian Units of the Northern Apennines of Italy
[Abstract in Rivista]
Remitti, F.; Vannucchi, P.; Bettelli, G.
abstract
2012
- Late orogenic deformation of the shallowest portion of an orogenic wedge: Coeval activity of extensional and compressional tectonics in the western Northern Apennines (Italy)
[Relazione in Atti di Convegno]
Carlini, M.; Artoni, A.; Vescovi, P.; Bernini, M.; Remitti, Francesca; Bettelli, Giuseppe; Vannucchi, P.; Aldega, L.; Balestrieri, M. L.; Corrado, S.; Torelli, L.
abstract
-
2012
- Lateral variability of the erosive plate boundary in the Northern Apennines, Italy
[Articolo su rivista]
P., Vannucchi; Remitti, Francesca; G., Bettelli
abstract
The early to middle Miocene erosive plate boundary preserved in the Northern Apennines NW of the Sillaro Line is formed by two distinct units - the Sestola-Vidiciatico Tectonic Unit and the Subli - gurian Units. These two units occupy, respectively, the SE and the NW portions of the studied area. Upon closer examination, the features that distinguish these mapped units do not reflect differing plate boundary processes, but rather the incorporation or non-incorporation of forearc-toe mass-wasting deposits into the active subduction channel. In other respects, these two units document similar subduction channel processes, including the contemporaneous activity of multiple sub-parallel slip surfaces. This mode of subduction channel deformation leads to the 'laminar' incorporation of distinct stacked slices within the channel. © 2012 Società Geologica Italiana, Roma.
2012
- Revisiting the Geology of the "Sillaro Line", Northern Apennines, Italy
[Articolo su rivista]
Bettelli, Giuseppe; Panini, Filippo; Fioroni, Chiara; Nirta, G.; Remitti, Francesca; Vannucchi, P.; Carlini, M.
abstract
-
2012
- Toward a dynamic concept of the subduction channel at erosive convergent margins with implications for interplate material transfer
[Articolo su rivista]
P., Vannucchi; F., Sage; J., Phipps Morgan; Remitti, Francesca; J. Y., Collot
abstract
Convergent plate boundaries accommodate intraplate displacement within a 100–1000 m thick shear zone. Marine geophysicists typically define this zone, the subduction channel (SC), as the sedimentary layer between the downgoing oceanic crust and the base of the upper plate. Geologists and modelers, instead, per-ceive the SC as a specific type of shear zone. The original theory of SCs was developed when the net accretion of marine sediments to the forearc was thought to typify a convergent margin. While erosive margins were briefly mentioned, their mechanics were not discussed in any detail. We now realize that subduction erosion is taking place at roughly half of the modern subduction margins. Here we review and revise the theory of erosive SCs (1) to unify this concept across disciplines, focusing on the meaning of the channel’s boundaries; (2) to redefine the portions of the forearc included in the SC concept; and (3) to better idealize this dynamic system where material supply to the channel, fluid content, and the heterogeneity of deformation all influence the SC’s upper and lower boundaries. Migration of the channel boundaries controls the downdip variation of tectonic mechanisms that shape the margin. Within the shallow, <15 km deep part of the SC, a gradual change of physical properties defines three zones; zone 1 of rapid fluid dewatering, zone 2 of overpressure, and zone 3 with metamorphic fluid release. A SC is a dynamic feature with along-strike and downdip variations caused by changes in channel material, in trapped fluid contents, and in interplate boundary geometry.
2011
- Incrementally developed slickenfibers — Geological record of repeating low stress-drop seismic events?
[Articolo su rivista]
Å., Fagereng; Remitti, Francesca; R. H., Sibson
abstract
An accretionary mélange of Triassic age ocean floor sediments exposed in the Chrystalls Beach Complex, South Island, New Zealand, comprises competent sandstone and chert phacoids set in a cleaved mudstone matrix, deformed in a continuous–discontinuous style at subgreenschist conditions. Deformation structures include a pervasive anastomosing fault–fracture mesh of multiple shearing surfaces, subparallel to cleavage, coated with incrementally developed quartz–calcite slickenfibers. Microstructural observations reveal slickenfiber growth by ‘crack-seal’ shear slip increments of 10–100 μm, with incremental slip transfer of the same order accommodated by opening of extension fractures that link en echelon slip surfaces. Individual slip surfaces can be traced for meters to tens of meters so that the ratio of average slip, u, to potential rupture length, L, predominantly lies within the range, 10− 6 < u/L < 10− 5, characteristic of microearthquakes obeying ‘constant stress-drop’ scaling with a low stress-drop Δτ ~ 30 kPa, typical of low frequency earthquakes. The host-rock assemblage, metamorphic environment, inference of near-lithostatic fluid overpressures, low stress-drop and mixed continuous–discontinuous shearing, resemble conditions and characteristics of low frequency earthquakes as identified within the seismic signals recorded during episodic tremor and slow slip events, at the downdip end of the seismogenic subduction thrust interface and within accretionary prisms.
2011
- Regional and local trends of maximum burial and exhumation timing
in the Northern Apennines of Italy: a new updated dataset of low-temperature thermal and thermochronological data integrated with geological constraints
[Abstract in Rivista]
M., Carlini; A., Artoni; M., Bernini; P., Vescovi; Remitti, Francesca; Bettelli, Giuseppe; P., Vannucchi; M. L., Balestrieri
abstract
-
2011
- Tectonic and sedimentary evolution of the frontal part of an ancient subduction complex at the transition from accretion to erosion: the case of the Ligurian wedge of the Northern Apennines, Italy
[Articolo su rivista]
Remitti, Francesca; Vannucchi, P.; Bettelli, Giuseppe; Fantoni, L.; Panini, Filippo; Vescovi, P.
abstract
Subduction can be either associated with accretion or removal of material from the overriding plate. These two processes can coexist or alternate in time along the same margin. Theirinception has the potential to change the dynamic equilibrium of a margin wedge resulting in the development of out-of-sequence thrusts, normal and strike-slip faults or large submarine landslides in the frontal part of the subduction zone.In this work we investigate the effects of the transition from frontal accretion to frontal erosion on the stability of a subduction complex through the study of a fossil example from the Northern Apennines.New structural data suggest that in the Aquitanian the removal and underthrusting of the toe of the wedge, formed by both the accreted sediments of oceanic affinity and the overlying wedge-top basin fill (i.e., the Subligurian Units), implied a process of frontal tectonic erosion. The presence, on top of the subduction complex, of a complete succession of mid-late Eocene to late Miocene slope apron sediments - i.e., the Epiligurian succession - allowed to reconstruct the sedimentary response to thisevent.In the Aquitanian large areas of the wedge were denudated of the lower-slope sedimentary cover through extensive gravitational mass movements. The subsequent deposition of a thick body ofsubmarine debris flow has been documented. The mass-wasting deposits are interpreted as the sedimentary response to the underthrusting of the frontal part of the Ligurian subduction complex formed by the Subligurian Units.
2011
- Thermal and geological constraints for the
timing of the activity the frontal part of an ancient subduction channel, Northern Apennines of
Italy
[Abstract in Rivista]
Remitti, Francesca; P., Vannucchi; M. L., Balestrieri; Bettelli, Giuseppe
abstract
-
2010
- Deformation and Fluid Flow in an Ancient Erosive Subduction Channel: Insight from the Northern Apennines of Italy
[Abstract in Rivista]
Remitti, Francesca; P., Vannucchi; L., Dallai; C., Boschi
abstract
-
2010
- Deformation and fluid circulation in an erosive subduction channel: Constraints from structural and isotopic studies of the ancient analogue of the northern Apennines of Italy
[Relazione in Atti di Convegno]
Vannucchi, P.; Remitti, Francesca; Boschi, C.; Bettelli, Giuseppe; Dallai, L.
abstract
-
2010
- Fluid history related to the early Eocene-middle Miocene convergent system of the Northern Apennines (Italy): Constraints from structural and isotopic studies
[Articolo su rivista]
Vannucchi, P.; Remitti, Francesca; Bettelli, Giuseppe; Boschi, C.; Dallai, L.
abstract
The late Eocene-middle Miocene erosive plate boundary between the European and Adriatic plates is exhumed in the Northern Apennines of Italy. The fossil fault zone is 500 m-thick and the outcropping portion exposes the first 5 km of its depth extent. At this plate boundary basal and frontal tectonic erosion incorporated unlithified, fluid-rich sediments into the fault zone. The deformation and nature of the material along the plate boundary define a fossil subduction channel. Here we couple a detailed structural analysis of the Apennine subduction channel, focusing in particular on calcite veins, with a stable isotope analysis to characterize the fluid regime along an active subduction channel.The 13C and 18O composition of calcite vein and host rock samples within the fault zone indicates that there is a deep metamorphic source of fluids migrating upwards along the subduction channel, in addition to locally derived fluid components. Dewatering of subducting turbidites only contributes significantly in the shallowest part of the channel. Structural observations indicate fluid flow along and across the subduction channel. At deep levels, fluid flow is associated with discrete deformation events on shear faults offset by dilational jogs filled with implosion breccias. At intermediate levels, deformation is still cyclic and associated with repeated crack-and-seal events. At the shallowest levels, deformation occurred while portions of the subducting material were still unlithified. Here the deformation is quasi-continuous without associated vein development. Both isotope and structural analyses indicate that this erosive subduction channel behaved as a weak fault with a vertical maximum principal stress.
2010
- Material trajectories in the frontal part of an ancient subduction channel
[Abstract in Rivista]
Remitti, Francesca; P., Vannucchi; M. L., Balestrieri; Bettelli, Giuseppe
abstract
-
2010
- Multidisciplinary geological excursion in the open-air laboratory of the Island of Malta. 11-18 November 2010. Field-Trip Guide.
[Monografia/Trattato scientifico]
Soldati, Mauro; Barbieri, Massimo; S., Biolchi; Buldrini, Fabrizio; Devoto, Stefano; E., Forte; S., Furlani; Gualtieri, Alessandro; Lugli, Stefano; M., Mantovani; A., Mocnik; Padovani, Veronica; A., Pasuto; Piacentini, Daniela; Prampolini, Mariacristina; Remitti, Francesca; J., Schembri; Tonelli, Chiara; Vescogni, Alessandro
abstract
Si tratta della guida all'escursione geologica multidisciplinare tenutasi a Malta dall'11 al 18 novembre 2010, nell'ambito del progetto di internazionalizzazione dell'Università di Modena e Reggio Emilia dal titolo "Multidisciplinary research in the open-air laboratory of the island of Malta: an internazional network for landslide hazard assessment in coastal areas" (2008-2010) finanziato dalla Fondazione Cassa di Risparmio di Modena e Reggio Emilia, per i Corsi di Laurea Triennale in Scienze Geologiche e Magistrale in Scienze e Tecnologie Geologiche.
2010
- Shear veins observed within anisotropic fabric at high angles to the maximum compressive stress
[Articolo su rivista]
Å., Fagereng; Remitti, Francesca; R. H., Sibson
abstract
Some faults seem to slip at unusually high angles (>45°) relative to the orientation of the greatest principal compressive stress. This implies that these faults are extremely weak compared with the surrounding rock. Laboratory friction experiments and theoretical models suggest that the weakness may result from slip on a pre-existing frictionally weak surface, weakening from chemical reactions, elevated fluid pressure or dissolution–precipitation creep. Here we describe shear veins within the Chrystalls Beach accretionary mélange, New Zealand. The mélange is a highly sheared assemblage of relatively competent rock within a cleaved, anisotropic mudstone matrix. The orientation of the shear veins—compared with the direction of hydrothermal extension veins that formed contemporaneously—indicates that they were active at an angle of 80°±5° to the greatest principal compressive stress. We show that the shear veins developed incrementally along the cleavage planes of the matrix. Thus, we suggest that episodic slip was facilitated by the anisotropic internal fabric, in a fluid-overpressured, heterogeneous shear zone. A similar mechanism may accommodate shear at high angles to the greatest principal compressive stress in a range of tectonic settings. We therefore conclude that incremental slip along a pre-existing planar fabric, coupled to high fluid pressure and dissolution–precipitation creep, may explain active slip on severely misoriented faults.
2009
- Early forefront exhumation in an erosive subduction complex: insights from the Northern Apennines of Italy
[Relazione in Atti di Convegno]
Remitti, Francesca; Vannucchi, P.; Balestrieri, M. L.; Bettelli, Giuseppe
abstract
Stratigraphic and structural data indicate that, at the beginning of the Miocene, the frontal part of the subductioncomplex of the Northern Apennines was removed and incorporated in a subduction channel formed duringongoing continental subduction.This stage follows the cessation of the growth of the accretionary prism by offscraping, occurred in the middleEocene. The switch to subduction dominated by frontal tectonic erosion, lasting at least to the middle Miocene, was followed by the exhumation of the chain.The exhumation history associated with accretion and retreat of the Northern Apennines has been analyzed through apatite thermochronology. The internal part of the chain started to be exhumed at 10-13 Ma, while the core of the Apennines began only at 8 Ma.Here we present new structural and thermochronological data from a tectonic mélange involved in the shallow part of the plate boundary. This mélange is composed by blocks dated from Late Cretaceous to late Oligocene. All the samples analyzed were exhumed starting at 22-17 Ma (early Miocene), hence the exhumation of the mélange occurred after short time period from its incorporation in the subduction channel and before its deactivation.Our data show that during the early stages of continent-continent subduction two simultaneous and apparently competing mechanisms were particularly actives: i) frontal and basal tectonic erosion leading to the development of a subduction channel, and ii) occasional shallow underplating leading to early exhumation of portions of the channel closely inboard. As both tectonic erosion and internal thickening, the last resulting in underplating, coexist during wedge development, they account for space variations in strain localization and material transfer.
2009
- Incrementally Developed `Dilational Hydro-Shears' Forming at High Angles to σ1 in Foliated Mélange Matrix
[Abstract in Rivista]
Å., Fagereng; Remitti, Francesca; R. H., Sibson
abstract
-
2009
- New thermal constraints on a shallow fossil subduction channel from the Northern Apennines of Italy
[Relazione in Atti di Convegno]
Carlini, M.; Aldega, L.; Corrado, S.; Vannucchi, P.; Remitti, Francesca; Bettelli, Giuseppe
abstract
Here we present new thermal constraints (with special regard to vitrinite reflectance, Illite percentage in Illite- Smectite mixed-layers and Kübler Index) derived from both XRD analysis of clay and optical analysis of organic matter dispersed in sediments incorporated in the Apennine erosive subduction channel. This study has the goal to define the distribution of maximum paleo-temperatures in different portion of the subduction channel as well as in the units representing its footwall and hanging wall. We then discuss the results with regards to the time-spacetectonic evolution.In the Northern Apennines of Italy, two tectonic units have been recently recognized as an ancient shallow subduction channel. The subduction channel is represented by the Sestola-Vidiciatico Tectonic Unit and its lateral equivalent, the Subligurian Units. The channel started to form at the transition from subduction to collision between the European and the Adria plates and it was active at least until the middle Miocene. The subduction channel is presently sandwiched between the former oceanic accretionary wedge - the Ligurian thrust nappe - and the underlying Adria sedimentary units deformed by folds and thrusts. The channel has a thickness of about 500 m and is representative of a portion ranging from the shallow diagenetic environment to temperatures of around 150°C, a critical temperature recognized in most of the subduction zones as coincident with the up-dip limit ofseismogenesis.The main component of the subduction channel is represented by material incorporated through frontal tectonic erosion removing the toe of the Ligurian/Subligurian wedge. This toe consisted of former accreted oceanic sediment and their slope deposits, the latter often reworked through gravitational processes. Basal tectonic erosion is shown by blocks of Ligurian rocks tectonically incorporated in the subduction channel. These blocks aregenerally located in the upper part of the mélange.Preliminary data from the clay mineral analysis from the Sestola-Vidiciatico Tectonic Unit and Subligurian Units indicate I% in I/S in a range between 80 and 90% and KI between 0.63 and 0.77. The analysis of organic matter gives Ro% generally in the mature stage of hydrocarbon generation with estimated paleo temperatures between 80°C and 140°C. The data from the footwall are highly variable -from thermally immature to mature- and allow to detect the changes in thickness of the hangingwall and the channel, i.e. the overthrust Ligurian wedge and the Sestola-Vidiciatico Tectonic Unit and Subligurian Units.
2009
- The aseismic-seismic transition and fluid regime along subduction plate boundaries and a fossil example from the Northern Apennines of Italy
[Capitolo/Saggio]
Vannucchi, P.; Remitti, Francesca; Phipps Morgan, J.; Bettelli, Giuseppe
abstract
This paper reviews observations and theories for the aseismic-seismic transition in the megathrust between the incoming and overriding plates at a subduction zone. The temperature of the aseismic-seismic transition appears to be quite similar at erosive and accretionary margins, despite large differences between them in the lithology of the seismogenic subduction channel that composes the ‘megathrust’ plate interface. This fact, and the recent laboratory demonstration that both smectite and illite are velocity-strengthening in creep, suggests that the oft-postulated change in mechanical behavior of the megathrust due to a smectite-illite clay mineral transformation at ~150°C is not the cause of the onset in seismogenesis at these temperature conditions within the subduction channel. Field observations from fossil megathrust zones suggest that a temperaturedependent change in the availability of in-situ fluid is likely to play a key role in the onset of seismogenesis. Perhaps the causal link is to the smectite-illite transformation and other metamorphic dewatering reactions that liberate water at ~150°C, under conditions where these reactions are an important local source of hydrous fluids. Field studies of fossil megathrusts support the hypothesis that fluids ‘control’ seismogenesis, and indicate that there are large fluid pressure variations during the seismic cycle. In the fossil erosive megathrust system preserved in the Apennines, two décollements are simultaneously active at the roof and base of the subduction channel. The uppermost (non-seismogenic) portion of the megathrust even appears to alternate between tensional and compressional modes of failure during the seismic cycle along the deeper portions of the megathrust.
2008
- Collecting a multi-disciplinary field dataset to model the interactions
between a flood control reservoir and the underlying porous aquifer
(abstract)
[Abstract in Atti di Convegno]
Borgatti, L.; Corsini, A.; Chiapponi, L.; D'Oria, M.; Giuffredi, F.; Lancellotta, R.; Mignosa, P.; Moretti, G.; Orlandini, S.; Pellegrini, M.; Remitti, F.; Ronchetti, F.; Tanda, M.; Zanini, A.
abstract
2008
- Geological record of fluid flow and seismogenesis along an erosive subducting plate boundary
[Articolo su rivista]
Vannucchi, P.; Remitti, Francesca; Bettelli, Giuseppe
abstract
Tectonic erosion of the overriding plate by the downgoing slab isbelieved to occur at half the Earth’s subduction zones. In situinvestigation of the geological processes at active erosive marginsis extremely difficult owing to the deep marine environment andthe net loss of forearc crust to deeper levels in the subduction zone.Until now, a fossil erosive subduction channel—the shear zonemarking the plate boundary—has not been recognized in thefield, so that seismic observations have provided the only information on plate boundary processes at erosive margins. Here we show that a fossil erosive margin is preserved in the Northern Apennines of Italy. It formed during the Tertiary transition from oceanic subduction to continental collision, and was preserved by the late deactivation and fossilization of the plate boundary. The outcropping erosive subduction channel is 500m thick. It is representative of the first 5km of depth, with its deeper portions reaching 150 C. The fossil zone records several surprises. Two decollements were simultaneously active at the top and base of the subduction channel. Both deeper basal erosion and near-surface frontal erosion occurred. At shallow depths extension was a key deformation component within this erosive convergent plate boundary, and slip occurred without an observable fluid pressure cycle. At depths greater than about 3km a fluid cycle is clearly shown by the development of veins and the alternation of fast (co-seismic) and slow (inter-seismic) slip. In the deepest portions of the outcropping subduction channel, extension is finally overprinted by compressional structures. In modern subduction zones the onset of seismic activity is believed to occur at 150 C, but in the fossil channel the onset occurred at cooler palaeo-temperatures.
2008
- Mass movements on the inner slope of a wedge at the transition from frontal accretion to frontal erosion: Evidence from a fossil analogue in the northern apennines of Italy
[Abstract in Atti di Convegno]
Fantoni, Laura; Bettelli, Giuseppe; Panini, Filippo; Remitti, Francesca; Vannucchi, P.
abstract
Submarine mass movements are sedimentary phenomena abundant in both present-day seafloor setting and in the sedimentary record of ancient basins. For this reason they represent one of the most important processes in the destruction of submarine margins and sediment redistribution. The investigation of ancient mass movements in on-land examples recorded in former sedimentary basins is particularly important because it may provide insights into the features of their modern submarine correspondent. The study of fossil analogues offers, in fact, a more detailed source of information on internal structures, depositional processes and post-depositional deformation history than the present-day submarine examples.In the Northern Apennines of Italy, both stratigraphic and structural data suggest a vast removal of the frontal part of the Ligurian accretionary prism through a large-scale process of tectonic erosion, in the early Miocene. This caused the destabilization of the forearc and the development of a distinct, large-scale mass-wasting event - the Canossa Event - which resulted in the collapse of the whole inner lower-slope of the foredeep. The slope failure is well recorded in the sedimentary infill of the external basins of the epi-Ligurian sequence, representing the lower portion of the original slope, where the sediments older than the Aquitanian are totally missing or represented by few scattered blocks ranging in size from several metres to several hundred metres (rarely few kilometres) and few hundred metres thick. As a consequence of this mass-wasting event, large submarine debris flow deposits, reworking material from the underlying accretionary Ligurian wedge, have been generated. They are now represented by the Aquitanian epi-Ligurian Val Tiepido-Canossa argillaceous breccias which in vast areas of the Northern Apennines are unconformably sealing the Ligurian substratum and few remnants of pre-Aquitanian epi-Ligurian sediments.The Val Tiepido-Canossa argillaceous breccias, extending for about 300 km along strike, ∼10 km wide and ∼300 m thick, provide a prominent fossil example of the sedimentary response to the destabilization of a slope apron in a convergent setting, as a consequence of the removal of a wedge toe through frontal tectonic erosion processes. This catastrophic mass-wasting event, implying a large tectonic reorganization of the outermost part of an accretionary prism, is one of the largest on-land examples of fossil submarine landslides and is comparable with present-day mass-wasting deposits in similar plate tectonic setting.
2008
- Stable isotope constraints on fluid-pressure buildup cycles and fluid–rock interaction at the frontal part of the early Eocene-middle Miocene convergent system of the Northern Apennines (Italy)
[Abstract in Atti di Convegno]
Remitti, Francesca; Vannucchi, P.; Dallai, L.; Boschi, C.
abstract
Understanding the mechanical behavior of subduction megathrusts is intimately related to the characterization of their fluid regime. Stable isotopes help in characterizing the fluid regime that existed during megathrust development. Here we analyze the late Eocene-mid Miocene, erosive boundary between the European and Adriatic plates, now exhumed in the N. Apennines. 13C and 18O composition of 125 calcite veins and 83 host rocks have been analyzed from 4 transects of the 500 m-thick fault zone. Stable isotopes have been coupled with structural analysis. Field and microstructural observations suggest that the evolution of structures in the deeper portion of the outcropping megathust, correspondent to 5 km depth, was genetically linked to episodic high Pf, resulting in cyclic fluid-induced brittle deformation interspersed with aseismic ductile creep. δ18O and δ13C values vary from samples of host rock and veins. For the hangingwall rocks the δ18O values show a great variability for each transect if they relate to the previous accretionary prism, from -8.23 to -2.16‰ PDB. If they relate to the slope sediments the isotopic values within each transect are more uniform as well as shown for the footwall samples. The accretionary prism-related rocks are also characterized by a high variability of δ13C, from -1.28 to 2.29‰ PDB, as well as the slope sediment related rocks, from -1.82 to 0.92‰ PDB. Systematic variations of isotopic values are instead observed in the vein samples. In general they show a depletion in δ18O and a shift from mostly positive to negative δ13C values with respect to both the hangingwall and footwall. For the shear zone veins O- and C-isotopic composition tend to be more uniform irrespective of the host rock values. Different localities, though, have different linear trends of δ13C and δ18O values. In general the isotopic data are consistent with a fault architecture where the deformation results concentrated on an array of discrete faults.
2008
- Underthrusting followed by rapid exhumation in the frontal part of an erosive subduction complex: evidence from a fossil analogue of the Northern Apennines, Italy
[Relazione in Atti di Convegno]
Remitti, Francesca; Balestrieri, M. L.; Vannucchi, P.; Bettelli, Giuseppe; Fantoni, Laura
abstract
A tectonic mélange, composed of Late Cretaceous to late Oligocene blocks, crops out 20 km inland from the inferred front of an ancient subduction complex in the Northern Apennines (Italy).Apatite fission-tracks analysis has been performed on samples from representative mélange blocks. All the samples, after sedimentation, reached temperatures of about 80°-120° and were successively exhumed starting at 25 – 17 Ma. Stratigraphic and structural data suggest that the mélange was originated by underthrusting processes as a consequence of frontal tectonic erosion of the prism while apatite fission tracks analysis unravel that after a short time period they rapidly exhumed
2007
- Deformation in a subduction channel: anatomy of the shallow portion (T< 150°C) of an ancient analogue in the Northern Apennines of Italy
[Abstract in Atti di Convegno]
Remitti, Francesca; Bettelli, Giuseppe; Vannucchi, P.
abstract
In the Northern Apennines of Italy, an underthrust tectonic mélange represents the ancient analogue of a shallow subduction channel. This mélange (the Sestola Vidiciatico Tectonic Unit) has been formed during the collision between the European and the Adria plates and it is presently sandwiched between the former oceanic accretionary wedge – Ligurian thrust nappe - and the underlying fold–and-thrust belt formed by Adria sedimentary units. It has a thickness of about 500 m and it is representative of a portion ranging from the shallow diagenetic environment to temperatures of around 150°C, a critical temperature recognized in most of the subduction zones as coincident with the up-dip limit of seismogenesis. The main portion of the material forming the subduction channel is the product of frontal erosion taken place at the toe of the Ligurian prism, including its sedimentary cover, reworked through sedimentary and tectonic processes (i.e. frontal prism). Basal erosion is represented by blocks of Ligurian prism tectonically incorporated in the subduction channel and found in the upper part of the mélange.The younger deformation phase, as defined by cross-cutting relationship, is characterised by a strong difference in lithification of the various components which causes a clear partitioning of the deformation. The softer, less lithified components at the time of entrance in the subduction channel record the whole deformation evolution showing clear evidence of continuous and pervasive soft-sediment deformation passing to discontinuous brittle deformation concentrated along faults at deeper levels. Instead the components already hard at the time of entrance in the subduction channel show only the last and brittle stage of deformation. The latter developed when lithification of the softer blocks became as such that the mélange started to show a homogeneous behaviour as shown by the deactivation of the blocks’ boundaries as detachment surfaces. The strain regime in the shallow part of the subduction channel is extensional suggesting a very weak nature of the plate boundary. This character seems to be controlled by the presence of fluid and, for the deeper part, by the cyclical variation of the fluid pressure (fault-valve behaviour).
2007
- Double décollement zone bordering the subduction channel in an ancient erosive subduction complex: implications for seismogenesis
[Abstract in Atti di Convegno]
Vannucchi, P.; Remitti, Francesca
abstract
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2007
- Internal structure and tectonic evolution of an underthrust tectonic mélange: the Sestola-Vidiciatico tectonic unit of the Northern Apennines, Italy
[Articolo su rivista]
Remitti, Francesca; Bettelli, Giuseppe; Vannucchi, P.
abstract
The Sestola-Vidiciatico Tectonic Unit (SVTU) in the Northern Apennines is an underthrust tectonic melange presently sandwiched between the Tuscan-Umbrian foredeep units and the overlying Ligurian/Subligurian thrust-nappe. The SVTU has been generated during the collision between the European and the Adria plates and now it separates the former oceanic accretionary wedge -Ligurian/Subligurian thrust nappe-from the underlying fold-and-thrust belt formed by Adria sedimentary units. The collision caused an eastward migrating foredeep basin and the overthrusting of the frontal part of the Ligurian/Subligurian thrust-nappe on the subducting Adria margin. Part of the inner lower-slope sediments of the migrating foredeep basin have been unconformably deposited on a frontal prism formed by material already accreted in the Ligurian/Subligurian prism gravitationally and tectonically reworked. The frontal prism and its sedimentary cover have been progressively dragged down along the plate boundary zone generating the SVTU. The lower-slope sediments have been incorporated in the melange as they were not completely lithified, and they show a long deformation history ranging from continuous and pervasive soft-sediment deformation to discontinuous brittle deformation concentrated along faults and mainly controlled by cycles of fluid pressure as testified by the presence of crack-and-seal texture and implosion breccia in the veins.
2007
- Internal structure of an ancient analogue of an erosive subduction channel
[Abstract in Atti di Convegno]
Remitti, Francesca; Vannucchi, P.; Bettelli, Giuseppe; Fantoni, Laura
abstract
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2007
- Internal structure of an ancient analogue of an erosive subduction channel: the Subligurian Units of the Northern Apennines, Italy
[Abstract in Atti di Convegno]
Remitti, Francesca; Vannucchi, P.; Bettelli, Giuseppe; Fantoni, Laura
abstract
The Subligurian Units –SLU- were involved in the Apennine subduction system starting from the middle Eocene. At the time the SLU were part of the Ligurian prism forming the frontal portion of the European margin. The present geometric position of the SLU, sandwiched between the External Ligurian Units and the Tuscan Units, implies that later on these units have been underthrust all together moving from the toe of the prism to below the prismWith the subduction of the continental crust, the SLU show evidence to have accommodated the relative displacement between the two plates. In particular is possible to reconstruct a flow velocity gradient within the sub-Ligurian units that allows them to be considered a fossil analogue of a subduction channel as defined by Cloos and Shreeve (1988).The deformation of the SLU varies within the different stratigraphic components: the basal formation (i.e. Canetolo Shale and Limestone) shows the same deformation style of the External Ligurian Units, which has been interpreted as the product of frontal accretion during the subduction. Accordingly, the basal part of the SLU formed the frontal part of the middle Eocene accretionary prism. The unconformable overlying late Eocene-late Oligocene slope deposits (i.e. Passo del Ticchiano Shale and Limestone, Petrignacola Sandstone, Ponte Bratica Sandstone), do not maintain the same deformation style, but they rather seal this frontal part of the accretionary prism. Hence the SLU younger than late Eocene could be considered as epi-Subligurian units.We infer that from end of the epi-SLU deposition, the entire Subligurian package was incorporated in a subduction channel and, since the main portion of the material forming the subduction channel was previously part of the upper plate, the Northern Apennines entered a phase of subduction erosion. The input in the subduction channel was through frontal erosion, with incorporation of the prism toe, and basal erosion, represented by sparse blocks of External Ligurian Units found in the upper part of the subduction channel.The subduction channel then is structured in minor units that we can envision as sub-horizontal bodies separated by tectonic surfaces parallel to the boundaries of the subduction channel itself. These thrust-bounded packets are organized in a tectonic vertical stratigraphy with those including younger sediments laying closer to the basal décollement and those including older sediments laying closer to the roof décollement. This tectonic stratigraphy implies that more than one décollement was active within the subduction channel. In particular, it suggests that the different décollements subdivide portions of the subduction channel that moved at different velocities such as, considering the overlaying plate as fixed, the lower décollements moved faster. Décollements deactivation occurs at depth, where involvement of the SLU in the fold and thrust system of the Tuscan Units indicates complete locking.The subduction channel deformation is preserved within the epi-Subligurian formations and the Ponte Bratica Sandstone has been the focus of detailed structural analysis. As a main character the Ponte Bratica Sandstone has been affected by a regional boudinage both in NE-SW direction and in SE-NW direction. Within each package of unfolded strata, scattered mesoscopic, mostly disharmonic, tight to isoclinal folds are present together with evidence of soft sediment deformation. The attribution of this deformation features to processes active at the prism toe seems quite certain, but the driving force is still unclear. Subduction channel deformation features are, instead, the conjugate sets of extensional faults filled by calcite veins. They cut all the components of the subduction channel and often also the deactivated décollements suggesting a strong partitioning of the deformation among them. They also suggest that the shear stress is mainly accommodated in extension.
2007
- Sedimentary response to frontal tectonic erosion: the example of the early Miocene Ligurian wedge collapse (Northern Apennines of Italy)
[Abstract in Atti di Convegno]
Fantoni, Laura; Bettelli, Giuseppe; Panini, Filippo; Remitti, Francesca; Vannucchi, P.
abstract
N/A
2007
- The transition from frontal accretion to frontal erosion:evidence from a fossil subduction complex in the Northern Apennines of Italy
[Relazione in Atti di Convegno]
Fantoni, Laura; Remitti, Francesca; Bettelli, Giuseppe; Panini, Filippo; Vannucchi, P.; Carlini, M.; Pinter, T.
abstract
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2006
- Insights into the deformation of an underthrust tectonic mélange from the Northern Apennines, Italy.
[Abstract in Atti di Convegno]
Remitti, Francesca; Bettelli, Giuseppe; Vannucchi, P.
abstract
The Sestola-Vidiciatico Tectonic Unit (SVTU) in the Northern Apennines is an underthrust tectonic mélange presently sandwiched between the Tuscan-Umbrian foredeep “flysch” units and the overlying Ligurian/Subligurian thrust-nappe. The SVTU has been generated during the collision between the European and the Adria plates and now it separates the oceanic accretionary wedge from the underlying fold–and-thrust belt formed by Adria sedimentary units. The collision caused an eastward migrating foredeep basin and the overthrusting of the frontal part of the Ligurian/Subligurian thrust-nappe/accretionary prism on the subducting Adria margin. Part of the inner lower-slope and marginal sediments of the migrating foredeep basin have been unconformably deposited on a newly developed frontal prism formed by material already accreted in the Ligurian/Subligurian prism and gravitationally and tectonically reworked. The frontal prism and its sedimentary cover have been progressively dragged down along the plate boundary zone generating the Sestola-Vidiciatico tectonic mélange on top of the underthrust turbidites. The mélange has been generated under conditions ranging from the shallow diagenetic environment at the toe of the prism to temperatures of around 120°C. The research has been focused on the younger component of the mélange that has been deposited on the frontal prism generated by the tectonic and sedimentary reworking of the former Ligurian accretionary wedge. The underthrust lower-slope sediments incorporated in the mélange, as they were not completely lithified,, show a long deformation history ranging from continuous and pervasive soft-sediment deformation to brittle deformation concentrated along faults strongly controlled by the lithological proprieties of the components and by the cyclical evolution of the fluid pressure.In the first deformational stage the marly component has been pervasively sheared until the loss of the primary bedding, whereas the shaly component developed a penetrative scaly fabric. The sandstone beds have been cut crossed by hydroplastic conjugate shear bands with no grain breakage evolving to breaking concentrated on a sharp surface. During the last structural stage the mélange has been penetratively cross-cut by a spaced network of shear surfaces coated by calcite slikenfibres showing a characteristic crack-and-seal growth. The final state of strain of the mélange results in a stretching both parallel and perpendicular to the main direction of tectonic transport.
2005
- Direct and indirect evidence of material transfer from the upper to the lower plate: the integration between fossil and modern convergent erosional margins
[Abstract in Atti di Convegno]
Vannucchi, P.; Bettelli, Giuseppe; Ranero, C. R.; Remitti, Francesca
abstract
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2005
- Mechanism of deformation in a subduction channel at the transition between subduction and collision: The Sestola Vidiciatico Example, Northern Apennines (Italy)
[Abstract in Atti di Convegno]
Remitti, Francesca; Vannucchi, P.; Bettelli, Giuseppe
abstract
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2005
- Microearthquake slip increments recorded in quartz slikenfibers, Chrystalls Beach accretionary complex, New Zealand
[Articolo su rivista]
Remitti, Francesca; Sibson, R. H.
abstract
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2005
- Relation between soft sediment and brittle deformation in a melange formed at the transition from subduction to collision
[Abstract in Atti di Convegno]
Remitti, Francesca; Bettelli, Giuseppe; Vannucchi, P.
abstract
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