This paper describes a four-day field trip across the Alpine Corsica, the southern branch of the Alpine collisional belt made up of oceanic and continental units derived from the closure of the Ligurian-Piedmont Oceanic Basin, and the subsequent collision between the continental margins of Adria and Europe plates. On the first day, the relationships between the main tectonic units, i.e., the Upper Units, the Schistes Lustr & eacute;s Complex and the Lower Units, can be observed along an east-west transect from Bastia to Ile-Rousse. On the second day, the features of the Upper Units can be observed in the Balagne area, where an ophiolite sequence from the Middle to Late Jurassic period, along with its Late Jurassic to Late Cretaceous sedimentary cover, is clearly visible. This sequence, belonging to the Balagne Nappe, is characterized by the repeated occurrence of coarse-grained deposits supplied from the Europe continental margin, which makes it unique in the Alpine-Apennine belt. On the third day, the oceanic units of the Schistes Lustr & eacute;s Complex in the Golo Valley will be examined. This complex comprises several ophiolite sequences that were accreted to the Alpine wedge and deformed under conditions of pressure and temperature ranging from blueschist to eclogite facies. On the fourth day, the Lower Units in the Corte, Popolasca and Ponte Leccia areas are visited. These units represent slices of the thinned continental margin of the Europe plate that were involved in subduction prior to continental collision. Overall, this paper provides a comprehensive overview of the stratigraphic, deformational, and metamorphic features of Corsica, which is one of the most significant fragments of the Alpine collisional belt in the western Mediterranean region.

Double-verging collisional orogens record the superposition of subduction, collision, and post-collisional extension acting at different crustal levels over long timescales. The Alps-Apennines orogen preserves evidence of Late Cretaceous-Paleocene subduction of oceanic lithosphere, Eocene continental subduction, and a subsequent polarity reversal that led to west-dipping continental subduction during the Oligocene-Miocene. The core of this orogen was dismantled during the Middle Miocene, first by syn-collisional extension and later by subsequent post-collisional extension, related to the opening of the Tyrrhenian Basin during the Late Miocene-Pliocene period. As a result of this dismantling, fragments of deep crustal domains remain discontinuously exposed in the Tyrrhenian region.We present new structural, petrographic and geochronological data from Gorgona Island, which has been interpreted up to now as consisting of metamorphosed ophiolites tectonically overlaying their metasedimentary cover. However, our results support the reinterpretation of the metasediments as deriving from the Adria continental crust, which was involved in west-dipping continental subduction. The pressure peak metamorphism associated to the maximum burial is in this paper documented at 1.0-1.05 GPa and ~300 °C, then followed by a temperature peak at 0.80-0.95 GPa and 360-380 °C. These new findings suggest that during syn-collisional extension, deep structural levels belonging to distinct segments of the former collisional orogen were juxtaposed. Gorgona Island therefore preserves part of the deep core of the Alps-Apennines system, providing new insights into the tectonic configuration resulting from the interplay of continental subduction, polarity reversal, and extension in double-verging collisional orogens that have evolved over time and in different locations.

The structural map of Venaco-Altiani area features a well-preserved transect across the Alpine Corsica, ranging from the deepest structural level of the Schistes Lustr & eacute;s Complex represented by the Upper Castagniccia and Morteda-Farinole Units, to the Inzecca Unit. Especially it provides an uninterrupted exposure of the Inzecca Unit, allowing the complete reconstruction of its lithostratigraphy and tectonic setting. It comprises high-pressure/low-temperature metamorphic ophiolites, which are overlain by a thick composite sequence of metasediments ranging from the Late Jurassic to the Late Cretaceous. From bottom to top, these include the metaradiolarites, Erbajolo, Petraggiolo and Bagliacone-Riventosa Formations. The latter two consist of siliciclastic and carbonatic metaturbidites that were deposited on top of the oceanic crust of the Ligurian-Piedmont basin. To the W, the Schistes Lustr & eacute;s Complex is bounded by Hercynian Corsica via N-S trending strike-slip faults. All the mapped tectonic units were affected by Alpine deformation and metamorphism.

In this article, we provide new biostratigraphic and structural data of the foredeep-derived Falterona Unit in the Arezzo area (Italy), to reconstruct the steps of evolution of the fold-and-thrust front-foredeep Apennine system. The sedimentary succession has been deposited in the N-S trending, foredeep basin bounded westward by the Apennine orogenic wedge and eastward by the Adria continental margin forebulge. The Falterona Unit mainly consists of the Monte Falterona Fm., a succession of Chattian–Late Aquitanian siliciclastic turbidites topped by the Vicchio Fm., characterized by Late Aquitanian–Early Serravallian slope deposits. The siliciclastic turbidites are interbedded with debris flows and carbonate turbidites supplied from the Apennine front and the forebulge, respectively. The foredeep basin in which the Monte Falterona Fm. deposited also includes the Macigno Fm. (Tuscan Nappe), that sedimented along the westernmost edge of the basin until its underthrusting and the subsequent migration of the fold-and-thrust system toward E. At this stage, the Monte Falterona Fm. has been transferred close to the fold-and-thrust front, triggering the sedimentation of the debris flows. In the Late Aquitanian, the Monte Falterona Fm. has been accreted to the wedge and the sedimentation of the Vicchio Fm. started.

This paper presents results of the first attempt to date a normal fault system that affected the eastern side of the Alpine Corsica (France). The U-Pb method was employed to date carbonate material with associated As-Sb mineralization in the Matra Fault, a N-S striking normal fault located southward of the Castagniccia dome. This fault cuts the Alpine nappe stack, here consisting of two oceanic-derived tectonic units, including Middle-Late Jurassic metaophiolites and/or related Early Cretaceous metasediments. From the Late Cretaceous onward, these units were involved in subduction processes and record peak eclogite facies metamorphism. After a complex exhumation path to the surface, these units then experienced long-lasting extensional tectonics linked to the collapse of the Alpine wedge, followed by two rifting stages. The first rifting stage occurred in the Oligocene-Early Miocene and the second in the Middle Miocene to Quaternary that caused the opening of the Liguro-Provencal and the Tyrrhenian back-arc basins, respectively. The U-Pb dating of the Matra Fault yields a weighted age of 9.80 +/- 0.37 Ma. Therefore, the Matra Fault developed, in association with syndeformational As-Sb-Fe sulfide mineralization, during the opening of the Tyrrhenian back-arc basin. This finding represents a significant advance in understanding the extensional tectonics in Corsica during the opening of the Tyrrhenian back-arc basin.

Trench basins related to an almost entirely subducted oceanic lithosphere are filled by deposits sourced from either the passive continental margin or the accretionary wedge. They also include large-scale submarine landslides often triggered by the inherited rough topography of the subducting plate. This mechanism provides the deposition of material by mass-transport processes from the wedge to the trench, resulting in highly heterogeneous trench sedimentation. The role of the mass-transport deposits in the accretion mechanisms, as well as their influence on seismic behaviour at the plate interface is difficult to assess in the active trenches, because of their limited accessibility. This study reports on a well-preserved fossil trench-fill sequence exposed in the Northern Apennines. A multidisciplinary survey including fieldwork, stratigraphy, biostratigraphy, geochemistry, and zircon provenance, allows reconstructing the anatomy of these deposits. The heterogeneities derived by distinct sediment packages made of mass-transport deposits and deep-sea turbidites reflect a setting with two feeding source areas: the accretionary wedge and the continental margin, respectively. Alongside the roughness of the subducting plate, this deposits association favours coherent underplating processes developed at depth. Such accretion mechanisms, linked to thrust faults at the base of the wedge, can generate both major earthquakes and new mass movements, reinforcing the complex role of trench-fill processes in subduction dynamics.

The Variscan basement in Corsica (France) is exposed as scattered metamorphic complexes preserved in the late Permian batholith in the south-western sector of the island. We present the first tectono-metamorphic map (at 1:10000 scale) of the Variscan high-grade metamorphic complex exposed in one of these complexes in the Fautea-Favone area (south-eastern Corsica). Our geological mapping distinguished the Fautea Migmatitic Complex (FMC), to the south, and the Tarcu-Favone Gneissic Complex (TFC), to the north. Considering the type and distribution of deformation structures, and lithotypes, the TFC and FMC are further divided in three sub-units. The two complexes are separated by a c. 1 km-thick zone where the two complexes are amalgamated in an anastomosed pattern (Transitional Units, TRU). Both complexes are lately affected by ductile to brittle localized shear zones with both dextral and sinistral kinematics, frequently bounding lozenge-shaped low-strain domains.

This paper presents a complete stratigraphic, tectonic, and structural dataset of the Internal Ligurian Units outcropping in the Antessio area (Northern Apennines), based on new geological mapping and micro-and mesoscale analyses. A stack of three Internal Ligurian Units, namely, from top to the bottom, the Gottero, Bracco-Val Graveglia and Colli-Tavarone Units, has been recognized. The general stratigraphic characteristics of these units indicate that they are derived from dismembering of a sequence derived from the Ligurian-Piedmont oceanic basin. This sequence includes Middle to Late Jurassic ophiolites, Late Jurassic to Late Cretaceous pelagic deposits, Late Cretaceous to Early Tertiary turbidites and Early Tertiary mass-transport deposits. This sequence is interpreted to have developed during the progressive trench-ward motion of a segment pertaining to the inner part of the Ligurian-Piedmont oceanic basin. In the Antessio area, the deformation history of the Internal Ligurian Units includes two deformation phases, whose features support the involvement of these units in a subductionrelated accretionary wedge zone by coherent underplating followed by exhumation. This picture suggests a close correlation between the Internal Ligurian Units of the Antessio area and those of the Bracco Massif, as well as those of the Graveglia and Vara valleys.

In the Corsica Island (France), the tectonic boundary along which the units of Alpine Corsica overlap the Hercynian Corsica represents a first-order structure which has not been investigated in depth yet. In this paper, the reconstruction of the Alpine Corsica Front in the Balagne area through the characterization of the deformation history and the associated peak metamorphism for the units of Alpine Corsica and for the Hercynian Corsica is provided. The collected data indicate that a gap in the peak metamorphism between the less metamorphic units located at the top of the unit pile, and those located at lower structural level which registered low-blueschist facies conditions exists. Also, a detailed structural analysis of the shear zones along the Alpine Corsica Front is supplied. The studied N-S trending, E-dipping shear zones documented at the western rim of the Balagne area are characterized by deformation history indicating a top-to-E sense of shear that overprint a former top-to-W kinematics. These findings indicate that the Alpine Corsica Front was affected by extensional tectonics after the shortening, which developed during the top-to-W thrusting of the Alpine Corsica onto the Hercynian Corsica. Framing our results in the regional tectonic setting, we suggest that the extensional tectonics documented in the Balagne area developed during the Oligocene-Early Miocene, i.e., during the transition from the latest stages of orogenic exhumation within the Alpine belt to the post-orogenic rifting stage in the Liguro-Proven & ccedil;al and Tyrrhenian Basins.

The Middle to Late Jurassic, high-pressure metamorphic ophiolites ofInzecca Unit are well exposed in the Noceta-Vezzani area ofAlpine Corsica. These metaophiolites were studied by using a multidisciplinary approach to reconstruct the architecture of the oceanic sector from which they derived. The collected data indicate that this oceanic crust consists of a mantle metaperidotites and metaophicalcites, both covered by massive or pillow metabasalts with or without a layer of ophiolite-bearing metabreccias. The field evidence indicates that the metaperidotites were exposed at the sea bottom and then covered by metabreccias and metabasalts. The metabasalts are intruded by plagiogranite dikes representing the last magmatic event referred to by U/Pb dating at the Kimmeridgian-Oxfordian. The metaophiolites were then covered by Early Cretaceous, hemipelagic sediments represented by metaradiolarites and by the calcschists of the Erbajolo Fm. Overall, all the features of these metaophiolites suggest its origin in an ultra-slow spreading ridge. In this frame, the origin of this ophiolite sequence is discussed, and its characteristics are compared with analogous examples from other sectors of the Alpine-Apennine belt.

In the Northern Apennines, the Internal Ligurian Units are considered deformed and metamorphosed fragments of the Ligure-Piemontese oceanic basin. In this paper, we report on the temperature and pressure conditions of the metamorphic peak for four Internal Ligurian Units, estimated using different geothermometers and geobarometers based on the white mica and chlorite compositions. These minerals were formed during the D1 deformation phase in the pre-Oligocene. The results indicate that the Portello and Gottero units are both characterized by metamorphic conditions pertaining to low blueschists facies, while the Colli-Tavarone and Bracco-Val Graveglia Units show a lower metamorphic imprint that produces assemblages of prehnite-pumpellyite facies. The estimated geothermal gradient for the metamorphic peak achieved by the analyzed Internal Ligurian Units during the D1 phase is 7–15 °C/Km, which is indicative of deformation in a subduction setting. Under these conditions, the D1 phase developed in these units as a result of underplating at the base of the accretionary wedge during the closure of the Ligure-Piemontese basin. These data indicate a close geodynamic correlation among the Internal Ligurian Units and the ophiolite-bearing units of the Alps.

This work presents the first pressure–temperature‐deformation‐time ( P–T‐d‐t ) path obtained for the Lower Units (Alpine Corsica, France) including the Tenda Massif that represent fragments of the European continental margin involved in the east‐dipping Alpine subduction. The new thermobarometric data applied to metapelites and the new 40 Ar/ 39 Ar dating of syn‐kinematic muscovite sampled from metagranitoids allowed us to define the P–T conditions and the age of the metamorphism of the Venaco Unit, a Lower Unit located in the southernmost sector of the Alpine Corsica. The outcoming scenario indicates that the Venaco Unit reached the baric peak at ≈ 33 km depth, not before Bartonian time. At 35.7 Ma (i.e., during the middle Priabonian), it was exhumed to a shallower structural level (i.e., at ≈ 26 km depth), mainly through the activation of the top‐to‐W shear zones. This retrograde path suggests that the Venaco Unit experienced fast exhumation, unlike the Tenda Massif which had been involved in subduction during the Ypresian and was stationary at 25–30 km, before its exhumation in the Priabonian.

In the Alpine Corsica, the Schistes Lustr & eacute;s Complex consists of a stack of high-pressure metamorphic oceanic and continental units originated during the Late Cretaceous-Middle Eocene closure of the Western Tethys oceanic basin. This complex also includes the Bagliacone-Riventosa Fm. i.e. a thick succession of metaturbidites, whose interpretation is still matter of debate. In this paper, we provide the stratigraphic, metamorphic, and structural evidence that the Bagliacone-Riventosa Fm. belongs to the sedimentary cover of the Middle to Late Jurassic metaophiolites of the Inzecca Unit. The reconstructed succession of the Inzecca Unit thus comprises metaophiolites topped by metacherts and by the Erbajolo, Pietraggiolo and Bagliacone-Riventosa Fms. The former two formations derived from hemipelagic deposits whereas the latter two include both siliciclastic and carbonate turbidites. This succession is affected by a polyphase deformation history that is recognized as the same in all the metasedimentary formations, as testified by their structural field relationships. In addition, these formations experienced the same pressure-temperature metamorphic path, indicating their involvement in a subduction zone. This picture provides new evidence for the mechanism of underplating and exhumation of the oceanic slices within the frame of the subduction zone that developed since Late Cretaceous in the Western Tethys oceanic basin.

Unveiling the pressure-temperature path of low-grade metamorphic rocks is challenging because of the occurrence of detrital minerals and high-variance mineral assemblages (i.e. chlorite-white mica-quartz). This paper is an attempt to reconstruct the pressure-temperature history on metapelites from a low-grade metamorphic unit, i.e. the Cabanaira Unit, located in the Marguareis Massif (Western Ligurian Alps, Italy). In order to obtain the most robust result possible, multi-equilibrium thermobarometry, forward modelling and crystallochemical index measurements are used together to reconstruct a pressure-temperature path, with consideration of the strengths and weaknesses of these methods.This multidisciplinary approach allowed us to reconstruct the metamorphic evolution of the unit of interest, characterised by a pressure peak reached under low-temperature conditions (0.85-0.68 GPa and 250-285 degrees C) followed by decompressional warming (low pressure-high temperature, 0.4-0.6 GPa and 300-335 degrees C).This pressure-temperature path is consistent with the tectonic evolution of the investigated area proposed by previous studies, where a geological scenario in which the Cabanaira Unit experienced subduction-related processes was postulated, even if the reasons for warming remain unclear.Multi-equilibrium thermobarometry is considered to be the most suitable method to unravel the metamorphic history of low-grade rocks, whereas forward thermodynamic modelling and the calculation of crystallochemical indexes seem to resolve only some segments of the pressure-temperature path.

The External Ligurian Units are regarded as representative of the ocean continent transition between the Ligure‒Piemontese oceanic basin and the hyperextended Adria continental margin. The remnants of this transition are preserved as slide blocks embedded in a sedimentary mélange. This mélange sedimented during the Santonian to Campanian in the rear of the accretionary wedge that developed during the east-dipping subduction of the oceanic lithosphere below Adria. The main characteristic of this mélange is the occurrence of slide blocks of subcontinental mantle, lower continental crust, granitoids, gabbro, basalt and sedimentary rocks in a sedimentary matrix. In this paper, we provide petrographic observations coupled with U‒Pb zircon ages and δ 18 O zircon isotopes of the slide blocks of felsic granulites and granitoids. U‒Pb data indicate ages ranging from Neoproterozoic to Late Triassic. δ 18 O isotopes help to define the source of the magma of granitoids and felsic granulites, which was the continental crust. Overall, the collected data indicate that the slide blocks from sedimentary mélanges can be regarded as true archives that are able to provide useful constraints about the geodynamic history of the source area of these deposits. Supplementary material: The dataset related to the U–Pb and ∂ 18 O analysisis available at https://doi.org/10.6084/m9.figshare.c.6922535 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

In the Alpine Corsica(France), the Santa Lucia Nappe represents a peculiar unit preserving the unique relicts of Paleozoic lower to medium continental crust. It consists of composite basement affected by Permian granulite facies metamorphic conditions unconformably covered by a Late Cretaceous clastic sequence(Tomboni Conglomerate and Tralonca Flysch) affected by polyphase deformation and low-grade-metamorphism. In this work, we present a new reconstruction of the deformation events registered by the Tralonca Flysch during the Alpine orogeny. The D1 phase was testified by rare isoclinal folds. The D2 phase produced a continuous foliation and a map-scale sheath-fold with a top-to-W sense of shear. The D3 phase produced E-verging non-cylindrical folds and S3 crenulation cleavage that is not associated to metamorphic blastesis. We present the first temperature-pressure-deformation(P-T-d) path for the Tralonca Flysch, demonstrating that the Santa Lucia Nappe underwent accretion and then first stage exhumation in the Alpine wedge during the D1 phase with pressure and temperature peaks both occurred under blueschist metamorphic conditions. The D2 phase occurred at lower pressure-temperature conditions during a second stage exhumation. This pressure-temperaturedeformation path is comparable with those of the Lower Units(i.e., the subducted continental units of Alpine Corsica) suggesting a common geodynamic history.

The Internal Ligurian units (Northern Apennine) represent deformed and metamorphosed fragments of the oceanic lithosphere of the Ligure-Piemontese oceanic basin. Different tectonic models have been proposed for the geodynamic setting in which the deformation and metamorphism have been acquired. However, the lack of updated, clear, thermo-barometric data has made it hard to unambiguously discriminate between these different proposed models. In this article, we provide evidence for the deformation of the Palombini Shale, i.e., pelagic deposits belonging to the Internal Ligurian units, under P and T peak conditions of 230-300 degrees C. and 0.6-0.9 GPa, respectively. These data indicate that the Internal Ligurian units were affected by a blueschist facies metamorphism achieved during the underplating within the accretionary wedge developed during the Late Cretaceous-Early Tertiary Alpine subduction. These data support the hypothesis of a unique, pre-Oligocene orogenic system for the Alpine belt and the westernmost sector of the Northern Apennines belt.

In the late Eocene, the peripheral portion of the European margin was involved in the Alpine subduction/exhumation processes. Witnesses of this event are the polyphase deformation and the metamorphism registered by slices of continental crust which compose the Lower Units, i.e. a set of tectonic units placed at the lowest structural level of the Alpine Corsica (France). The pressure-temperature-deformation-time (P-T-d-t) path of one of them named Venaco Unit was traced by using an integrated set of data related to the phyllosilicates which dynamically recrystallized in the metagranitoids and metapelites. Different thermobarometric tools were applied to the chlorite and white mica crystals selected in the microdomains of the metapelites of the Venaco Unit. The 40Ar/39Ar dating was instead applied on syn-kinematic muscovite sampled from metagranitoids of the Venaco Unit. The results indicates that the Venaco Unit reached the baric peak at ≈ 33 km depth and was exhumed at shallower structural level (i.e., at ≈ 26 km depth) in the middle Priabonian. This retrograde path suggests that the Venaco Unit experienced fast exhumation through the activation of the top-to-W shear zones.

The Bajgan Complex in the North Makran Domain (Makran Accretionary Prism) comprises disrupted meta-ophiolitic sequences originating from oceanic crust protoliths. They include ultramafic and mafic cumulates, isotropic gabbros, plagiogranites and basalts. Ultramafic-mafic cumulates and plagiogranites exhibit compositions akin to rocks formed in mid-ocean ridge settings. Isotropic gabbro and basalt protoliths can be subdivided into three distinct geochemical types. Type-1 rocks are sub-alkaline (Nb/Y < 0.1) with low Th, Nb and Ta contents and La-N/Yb-N ratios <1, resembling those of normal mid-ocean ridge basalts (N-MORB). Type-2 rocks display slight enrichment in Th, Ta, Nb (Nb/Y = 0.36-0.45) and La-N/Yb-N = 2.12-3.20, resembling the chemistry of enriched (E-) MORB. Type-3 basalts show an alkaline nature (Nb/Y = 0.88-1.82), significant Th, Ta and Nb enrichment, and high La-N/Yb-N ratios (7.01-20.08), resembling the chemistry of alkaline basalts (ocean island basalts, OIB). Petrogenetic modelling indicates that N-MORB protoliths originated from a depleted MORB mantle source, whereas E-MORB and OIB protoliths were generated from partial melting of sub-oceanic depleted sources that underwent varying degrees of OIB-type enrichment. The Bajgan meta-ophiolitic protoliths were formed within a Late Jurassic to Cretaceous oceanic basin influenced by mantle plume activity and plume-ridge interaction.