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The Corno Alto complex represents the onset of the intrusive igneous activity during the Alpine Orogen and for this reason has particular importance in the interpretation of the geodynamic evolution of the Alps. Whole-rock chemistry of the granitoid rocks of the Corno Alto complex reveals peculiar features with respect to the other units of the Adamello batholith, and to typical I-type and S-type granitoids. In particular, the Corno Alto rocks are enriched in Ba, Sr and La/Yb at any given SiO2 content. U[sbnd]Pb geochronology on zircon suggests an incremental assembly of the Corno Alto complex by multiple and possibly discrete magma injections in a time span of about 5 Myr starting from 44 Ma. The different zircon domains have significantly distinct Hf isotopic signature (up to 18 ɛHf units of variation) with some values trending towards the isotopic composition of the depleted mantle (DM). Bulk major and trace element geochemistry together with in-situ Hf isotope composition of zircon allow to distinguish at least two geochemically components in the Corno Alto rocks: i) a high Ba component characterized by high Sr and La/Yb ratios, likely derived from melting of carbonate sediments of slab origin; ii) a juvenile component with Hf isotopic signature close to the DM and capable to crystallize plagioclase with An90, which is interpreted as the primitive mantle signal. This work constrains for the first time the occurrence of a slab derived carbonate input in the mantle-derived melts during the onset of the Alpine magmatism (dated at 44 Ma). The anomalously high thermal conditions required to induced carbonate melting may reflect the rise of asthenospheric material near the torn edge of the European slab where the Corno alto is located. Remarkably, these high thermal conditions parallel those at the Archean-Proterozoic transition and the Corno Alto complex could thus represent a kind of modern analogues of the high Ba/K sanukitoids.

Syn-rift extensional faults play a significant role during the early stage of rifting. Constraining the age of faulting, and how and when deformation shifts from the proximal to the distal margin areas, is crucial for the reconstruction of the rifting process. Previous assessments of the structural and temporal evolution of rift-related faults of the Adria proximal margin have primarily relied on indirect biostratigraphic evidence. Additionally, the majority of rift-related faults underwent tectonic inversion during the Alpine orogeny. In this study, in-situ U-Pb geochronology was applied on syn-kinematic calcites to unravel the activity of the Amora Fault, a remarkable example of a Jurassic growth fault unaffected by the Alpine orogeny. The obtained ages, spanning from Hettangian to Callovian, extend the AF activity beyond the previously established Early Jurassic time. This chrono-structural model has significant implications on the role of major extensional faults in focusing deformation throughout the rift system's evolution.

The Early Permian in the present-day Europe area was a time when a major tectonic shift occurred, leading from the tectonic collapse of the Variscan orogeny to the crustal extension and thinning that characterized the Early Permian times. Crustal extension was associated with extensive magmatism at different crustal levels: from gabbro in the lower crust or at the mantle/crust transition to subaerial high-SiO2 volcanic activity. In the whole Southalpine Domain, the Early Permian intrusive bodies occur from the west (e.g. Ivrea-Verbano Complex and “Graniti dei Laghi”) to the east (Ifinger, Brixen and Cima d’Asta intrusive complexes). Among these, in the central Southern Alps (comprised between the Giudicarie Belt and the Lake Como), minor intrusive complexes also occur. The Val Biandino Intrusive Suite consists of two magmatic units: the Val Biandino Quartz-Diorite (VBQD) and the Valle di San Biagio Granite (VSBG). The first of them consists of gabbro-diorite to granodiorite bodies associated with leucocratic cordierite-bearing granitic dikes that intruded the pre-Permian basement. To the west, a W-dipping normal fault of Permian age represents the boundary between this unit and the Valle di San Biagio porphyric granite. All rock varieties of the Val Biandino Intrusive Suite display a high-K calc-alkaline affinity with metaluminous to peraluminous character. Field crosscutting relationships point to a late generation of the cordierite granites of the Val Biandino Quartz-Diorite unit with respect to the more mafic types. SHRIMP U–Pb zircon dating provided an age of 285.2 ± 1.9 Ma for a cordierite granite of the Val Biandino Quartz-Diorite unit and 283.2 ± 1.9 Ma for the porphyric Valle di San Biagio Granite. Geochemical data suggest that gabbro-diorite, quartz-diorite, granodiorite and leucogranite are not co-magmatic. The existing gaps in term of SiO2 wt% and the higher HREE contents in mafic and intermediate rocks with respect to granite coupled with similar LREE in

Geodynamic models implying subduction of continental crust either consider this process happening during collision, when the continental margin of the lower plate attempts subduction, or in pre-collisional stages, when tectonic erosion of the upper plate or subduction of continental extensional allochthons drag continental crust in the subduction channel. In the Zagros orogen (W Iran), high-pressure rocks are known only from the Sanandaj-Sirjan Zone, NE of the Main Zagros Thrust. Here, eclogites of the North Shahrekord Metamorphic Complex suggest subduction of continental crust slices derived from the upper plate (Central Iran) during the onset of the Neo-Tethys subduction along the southern margin of Iran. Eclogites record a clockwise pressure-temperature-time path, with pre-eclogitic epidote-amphibolites-facies phase assemblages preserved in garnet cores, a high-pressure stage, and a subsequent retrogression at amphibolite-facies conditions. By means of forward thermodynamic modelling and 40Ar/39Ar geochronology, the peak metamorphism has been constrained at 1.9-2.1 GPa and 550-600 °C, in the 191-194 Ma time span. The following retrogression during exhumation lasted at least until 144 Ma. Our data suggest that the onset of the Neo-Tethys subduction traces back prior to 190 Ma, involving together with the Neo-Tethys oceanic lithosphere also slices of the upper plate continental crust scraped off by means of tectonic erosion processes.

The study of selected logs from the Central-Eastern Iran Microplate (CEIM; area of Arusan) and Sanandaj–Sirjan Zone (SSZ; areas of Esfahan east and Tiran) constrains timing and evolution of the Cretaceous successions, resting unconformably on older sediments or non-conformably on the metamorphic basement. The Cretaceous marine transgression occurred almost synchronously on a levelled topography, documenting a previous deep erosion. Above a basal siliciclastic unit, rudist- and orbitolinid-rich lower Aptian limestone (“Orbitolina Limestone”, Shak Kuh Formation, Taft Formation) were deposited. Later, the stratigraphic evolution of the three studied areas differentiates, documenting changes in the depositional environments, reflecting different subsidence rates. In the Tiran area, marls and cherty limestones covering shallow-water limestones record a deepening trend. A differentiation of depositional environment is observed at Arusan, where conglomerates to the west pass to basinal sandstone and marls to the east. Here, a Coniacian-Campanian reprise of the carbonate production (with skeletal limestones rich in rudists, ostreids, and abundant orbitoidids) is covered by cherty marls. In the Esfahan north area, glauconitic hardground marls covered by chert record important deepening during the early Cenomanian, followed by the reprise of shallow-water carbonate production (middle Cenomanian). The synchronous deposition of Aptian carbonate successions on large parts of the CEIM, SSZ and North-Iranian domains suggests a rapid regional transgression controlled by a sea-level rise. Stratigraphic differentiation occurring in late Aptian–Cenomanian times, recording the onset of tectonic events differently affecting the aforementioned domains, likely related to the opening of oceanic seaways in the CEIM and the SSZ.

The Cenozoic Adamello batholith in the Southern Alps records solid-state deformation structures including, in order of decreasing relative age, cooling joints, shear zones, and faults. In the present study, we constrained age and duration of each phase with 40Ar/39Ar geochronology. The Avio granodiorite, cooling joints, mylonites, pseudotachylytes, and cataclasites were characterized through microstructural, mineralogical, µCT and EPMA analyses. The dated K-bearing phases are: (i) magmatic biotite; (ii) biotite and K-feldspar in joints and mylonites; (iii) pseudotachylytes; and (iv) hydrothermal K-feldspar in cataclasites. The wall-rock biotite is 33.2 ± 0.2 Ma old, independent of grainsize, overlapping with the age of the cooling joints. Bulk biotite-rich mylonites have ages between 32.4 ± 0.5 and 30.8 ± 0.08 Ma. The K-feldspar cementing cataclasite is 25.5 ± 1.1 Ma old. Pseudotachylytes cluster between 29.8 ± 0.3 and 31.7 ± 3.1 Ma, one is 25.6 ± 0.3 Ma old. The resolvable difference in age between magmatic biotite and mylonites indicate that biotite is not a thermochronometer; as its age is mostly controlled by deformation and fluid-rock interactions. 40Ar/39Ar dates mostly confirm the relative ages determined from field relations, with mylonites active within a time window of 1.6 Ma and subsequent seismic faulting protracting for almost 6 Ma.

The central Southern Alps (N Italy) preserve stratigraphic evidence of the Early Jurassic rifting related to the opening of the Alpine Tethys, despite its later involvement in the Alpine orogeny. Here, the extensional tectonics produced rapid facies and thickness changes of the Liassic succession, interpreted as syn-rift deposits, documenting a horst and graben architecture postdating a Rhaetian shallow-water homogeneous succession. Despite the identification of several extensional syn-depositional faults bordering structural highs, no geochronological constraints were until now available to confirm the Early Jurassic age of these faults. In this work geochronological constraints obtained by LA-ICP-MS U-Pb dating on syn-tectonic carbonate veins associated with extensional faults are presented for the first time. Field work (Seriana Valley, N Italy) led to the identification of N-S trending syn-depositional faults, the Amora Fault System, that borders a deep half-graben filled with Lower Jurassic cherty limestones (Moltrasio Limestone). The syn-depositional activity of these faults is documented by stratigraphic evidence, different thickness of the hangingwall and footwall successions, and facies association (such as abundant slump overfolds and mass flow deposits). In the study area, clear cross-cutting relationships between structures and middle Eocene magmatic bodies document three main tectonic events: 1) the E-W oriented extensional phase; 2) a N-S oriented extensional phase characterized by the emplacement of andesitic dikes; 3) the N-S oriented Alpine compression. The relative age constraints permitted to focus on the E-W extensional phase, related to the opening of the Lombardian basin. Carbonate syn-tectonic veins and slickenfibers were sampled in the Norian to Lower Jurassic successions, both in the footwall and in the hangingwall of the Amora Fault System. O-C stable-isotopes analyses and U-Pb dating were performed on 21 samples, based on previous microstr

The Vinschgau Shear Zone (VSZ) is one of the largest and most significant shear zones developed under plastic conditions within the Austroalpine domain, juxtaposing the Ötztal and the Texel units to the Campo, Scharl and Sesvenna units during the building of the Eo-Alpine Orogen. The VSZ dominates the structural setting of a large portion of the central Austroalpine Late Cretaceous thrust stack. In order to fully assess the evolution of the VSZ, a multi-faceted approach based on detailed multiscale structural and petrochronological analyses has been carried out across representative transects of the shear zone in the Vinschgau Valley. The research has been performed with a view to characterizing kinematics, P-T conditions and timing of motion of the VSZ. Our fieldwork-based analyses suggest that the dip angle of mylonitic foliation increases from west to east with an E-W-trending stretching lineation which dips alternatively to the west and to the east, due to later folding related to the Cenozoic crustal shortening. The dominant top-to-W shear sense of the mylonites recognized in the field and confirmed by microstructural analyses led to exhumation of the upper Austroalpine nappes in the hanging wall of the shear zone; the Texel unit with Late Cretaceous eclogites and the Schneeberg and Ötztal units were all affected by Eo-Alpine amphibolite-facies metamorphism. Chemical and microstructural analyses suggest deformation temperatures of ca. 350-400C during shearing. Timing of deformation along the VSZ has been constrained for the first time through 40Ar/39Ar dating of syn-shearing micas, which reveal a Late Cretaceous age of the VSZ mylonites with ages ranging between 80 and 97Ma. A systematic younging age of deformation occurs towards the central part of the shear zone in the studied transects. Vorticity analysis shows a clear decrease in the simple shear component correlated to the younging of mica ages towards the core of the shear zone. This evolution is consis

The Borgo outcrop of the Monte Duria Area (Adula-Cima Lunga unit, Central Alps, Italy) is an excellent example of melt-peridotite interaction which occurred under a deformation regime at high pressure, that enabled the combination of porous and focused flow of eclogite-derived melts into garnet peridotites. Migmatised eclogites are in direct contact with retrogressed garnet peridotites and the contact is marked by a tremolitite layer, also occurring as boudins parallel to the garnet layering in the peridotites, derived from a garnet websterite precursor produced by the interaction between eclogite-derived melts with the peridotite at high pressure. LREE concentrations of tremolitite along a 120 m length profile, starting from the eclogite-peridotite contact to the inner part of the peridotite, show a progressive enrichment coupled with a peculiar fractionation. Numerical modelling assuming the eclogitic leucosome as the starting percolating melt reproduces the REE enrichment and LREE/HREE fractionation observed in tremolitite bulk rocks within the first 30 m. The comparison between the REE composition of the retrogressed garnet websterites along the profile and the result of our model suggests that reactive melt infiltration at high pressure is a plausible mechanism to modify the REE budget of mantle peridotites that lie on top of the subducting crustal slab.

At the end of the Variscan orogeny, several episodes of crustal extension starting in the Early Permian occurred in central Southern Alps (cSA), affecting the Adria passive margin (Handy et al., 1999). During this period, a megashear zone with dextral kinematics led to the transition from Pangea A to Pangea B configuration (Muttoni et al., 2003). The transtensional to extensional deformation regime led to the development of intra-continental basins infilled by Upper Carboniferous to Lower Permian sedimentary successions (Cadel et al., 1996). Crustal shortening related to Alpine compression was responsible for a partial or complete inversion of favourably oriented normal faults inherited from the Permian tectonics (Blom & Passchier, 1997). Despite this, SSE-dipping Early Permian Low-Angle Normal Faults (LANFs) are well-preserved because they exceptionally escaped most of the Alpine deformations. Their surfaces are within the Lower Permian sedimentary cover, or at the interface between the sedimentary cover and the Variscan basement, passing to intra-basement shear zones. Two major Permian LANFs (Aga-Vedello and Masoni faults) are recorded in the Pizzo del Diavolo Fm. along the northern border of the Permian Orobic Basin (N Italy). They are “non-Andersonian” normal faults whose surfaces are characterized by cataclastic bands usually sealed by centimetric to metric layers of dark grey to black aphanitic tourmalinites (Zanchi et al., 2019). Tourmalinites indicate fluids circulation channelled along high permeability fault zones and are related to magmatic-hydrothermal fluids that produced metasomatic tourmalines with different compositions at different distances from the fluid source, i.e. the crystallizing intrusive bodies. In addition to Aga-Vedello and Masoni faults, further exposures of Permian LANFs occur in other sectors of the cSA and they are always associated to the presence of tourmalinites. Several authors (De Capitani et al., 1999; Slack et al., 1996; Ca

Low-Angle Normal Faults (LANFs) represent in the central Southern Alps area (N Italy) the main structures along which the Variscan basement is in contact with the Upper CarboniferousPermian volcanic-sedimentary succession. Tourmalinites frequently occur along LANFs, usually replacing former cataclasites. The mineralogy and chemical composition of tourmalinites point to a metasomatic origin. LANFs, together with high-angle faults, controlled the opening of the Permian Orobic Basin and likely acted as a preferred pathway for hydrothermal fluids that triggered the Boron-metasomatism. Along the Aga-Vedello LANF, tourmalinites appear to have formed after the cessation of fault activity, as no brittle post-metasomatism deformation overprint has been observed. These relationships suggest that the circulation of B-rich fluids occurred after the opening of the Orobic Basin that is broadly constrained to the Early Permian. At the same time, ca. 285–270 Ma, a strong magmatic activity affected all the Southern Alps, ranging in composition from mafic to acidic rocks and from intrusions at deep crustal levels to effusive volcanic products. The Early Permian magmatism was likely the source of the late-stage hydrothermal fluids that formed the tourmalinites. The same fluids could also have played a significant role in the formation of the Uranium ore deposit of the Novazza-Vedello mining district, as the ore bodies in the Vedello valley are concentrated along the basement-cover contact.

The central Southern Alps (Seriana Valley, Bergamo) is characterized by a complex polyphasic evolution (Zanchetta et al., 2015) resulting from the re-activation of extensional faults related to the Jurassic rifting during the Alpine deformation, as well as the development of new structures. At least three different events were identified on the base of cross-cutting relationships between structures and magmatic bodies (Zanchi et al., 1990): 1) Early Jurassic N-S oriented normal faults, several kilometers in length, bordering a graben; 2) the intrusion of E-W trending andesitic dikes dated at 40 Ma (U-Pb zircon ages; D’Adda et al., 2011); 3) the reactivation of Jurassic normal faults as sinistral or dextral strike-slip faults during the N-S oriented Alpine compression, which caused southward translation of the Dolomia Principale dominated thrust sheet, probably during the late Cenozoic (Zanchi et al., 1990). To understand this complex tectonic evolution, field work has been performed North of Bergamo (Amora, Selvino area) where the transition from pre-rift (Rhaetian) to syn-rift (Hettangian) succession is preserved and where the Alpine tectonics, postdating this Jurassic extensional event, is well expressed by transcurrent and reverse faults. Furthermore, clear cross-cutting relationship between the main tectonic features are well exposed in this area; field work focused on the reconstruction of the geometrical features of reverse, normal and strike-slip faults, joints, and veins, allowing for the identification of at least three tectonic phases, as described by Zanchi et al. (1990). Field work led to the identification of a graben filled by Jurassic basin sediments whose bordering faults (N-S trending) were activated as transcurrent faults during the Alpine compression. Despite the Alpine reactivation, the syndepositional Lower Jurassic activity of these faults is documented by stratigraphic evidence, such as slump overfolds and mass flow deposits in the Lower Juras

The exhumation of the Lepontine Dome in the Central Alps was mainly driven by extensional shear zones at its borders. The Simplon Shear Zone (SSZ), formed as a consequence of east-west lateral extrusion perpendicular to north-south convergence between Adria and Europa plates, has been the leading structure in the exhumation of the western sector of the Lepontine Dome where the deepest rocks of Central Alps are nowadays exposed. We present here a multidisciplinary study of the SSZ combining fieldwork, microstructural analyses, vorticity estimates, quartz c-axis fabric analysis, quartz paleopiezometry and 40Ar/39Ar geochronology. The SSZ evolved from epidote-amphibolite to greenschist facies and then brittle conditions during shearing. A decrease of simple shear component from 88% to 37% towards the top of the shear zone is observed, with mylonites displaying ages within the 12-8 Ma time interval. Differential stress (59–78 MPa) and strain rate (10−11-10−12 s−1) estimates are in agreement with values obtained for crustal-scale low-angle normal faults developed at medium to shallow crustal levels. Our multiscale and multidisciplinary approach points out that the SSZ experienced a complex evolution, with shear strain heterogeneously distributed across the shear zone in the frame of a decrease of the simple shear component and increase of the differential flow stress toward the top of the shear zone.

The interplay of tectonic and climatic forcing in the development of Alpine deep-seated gravitational slope deformations (DSGSD) is still poorly understood. We investigate a giant DSGSD affecting the Piz Dora slope (Val Müstair, Switzerland) by geological, structural and geomorphological analyses, spaceborne SAR interferometry and numerical modelling. The DSGSD affects Permian terrigenous and volcanoclastic successions folded into a kilometre-scale asymmetric anticline during the Alpine orogenesis. The area is characterized by active tectonic uplift and widespread shallow seismicity with dominant dip-slip fault mechanisms, experienced fast deglaciation after the Last Glacial Maximum and periglacial conditions between the Lateglacial and Holocene. The slope is affected by morpho-structural features testifying to the deep-seated gravitational sliding of 1.85 km3 of rock along a basal shear zone over 400 m deep. Analysis of rock glaciers and DInSAR data show that the DSGSD was active in Lateglacial times and is presently deforming at rates ö 15 mm/yr. Integrated kinematic analysis of field and radar data outlines a key control of the inherited fold structure on the DSGSD, with a transition from deep compound sliding to the West, controlled by massive conglomerates (Chazforà Formation), to shallower roto-translational sliding to the East, controlled by volcanoclastic foliated rocks (Ruina Formation). 2DFEM stress-strain numerical models, simulating the post-LGM slope evolution in static, pseudo-static and dynamic conditions allowed evaluating the contribution of long-term seismicity to DSGSD in a paraglacial setting. Dynamic modelling was performed starting from the characterization of a real earthquake, representative of the recent local seismotectonic activity, and scaled to obtain dynamic scenarios with different return periods. Results suggest that deglaciation-related perturbations promoted the inception of the DSGSD but not its complete development, that was li

Peridotites of Ulten Zone (Eastern Alps, N Italy) show a transition from coarse protogranular spinel lherzolites to fine-grained amphibole + garnet peridotites, recorded by the crystallization of garnet coronas around spinel. Pyroxenite veins, transposed along the peridotite foliation, show a similar metamorphic evolution from coarse-grained (garnet-free) websterites to fine-grained garnet websterites. In both peridotites and websterites, garnet previously exsolved from porphyroclastic high-temperature pyroxenes and later crystallized along the foliation. This evolution has been interpreted to reflect cooling and pressure increase of websterites and host peridotites from spinel- to garnet-facies conditions. Microstructures and crystallographic orientation data indicate that the re-equilibration of garnet websterites in the garnet stability field occurred during deformation. Porphyroclastic pyroxenes have been interpreted to deform by dislocation glide and creep. In particular, TEM observations indicate the activation of the (100)[010] slip system in orthopyroxene. Core-and-mantle microstructures also suggest that dislocation creep was aided by subgrain rotation recrystallization, leading to the formation of neoblastic pyroxenes. These recrystallized grains deformed by diffusion-accommodated grain boundary sliding, as indicated by the occurrence of quadruple junctions and straight, aligned grain boundaries. The transition from dislocation creep to diffusion creep in websterites was accompanied by the crystallization of garnet along foliation, which triggered the pinning of the recrystallized matrix and stabilized the fine-grained microtexture for diffusion creep, promoting rheological weakening. Garnet websterites of Ulten Zone thus offer a unique opportunity to investigate the effects of reaction softening during the corner flow in the supra-subduction lithospheric mantle induced by the descending slab.

Proofs of synsedimentary tectonics during the Early Permian in the central Southern Alps (cSA, N Italy) are recorded in the volcanic and terrigenous successions of the Laghi Gemelli Group, which are characterized by the occurrence of abrupt facies variations often associated with coarse-grained deposits. These features are generally attributed to syn-sedimentary tectonic activity demonstrated by the local occurrence of sediments deformation such as liquefaction or slumping due to seismic shaking. Detailed fieldwork allowed us to recognize dewatering structures and sedimentary dikes, ball and pillars and small slumps, occurring along hundreds of mesoscopic faults showing meter-scale displacement in correspondence of high-angle conjugate systems as well as domino-style faults, often accompanied by growth structures. These structures are mainly concentrated in the fine-grained sediments of the Pizzo del Diavolo Formation, which were deposited on top of the volcaniclastic succession of the Ca’ Bianca Volcanite and crossed by seismogenic synsedimentary faults. The Permian synsedimentary structures of cSA are mostly associated with high-angle Andersonian normal faults which are combined with low-angle normal faults (LANFs) that developed along the interface between the Permian sedimentary cover and the Variscan basement. This LANFs system is relevant for the Permian hydrothermal circulation, resulting in widespread tourmalinites deposition along fault zones, and locally in U mineralization. According to our structural analysis the Permian tectonic setting is characterized by pure extension, dominated by ENE-WSW striking normal faults inverted during the Alpine shortening as high-angle reverse faults.

The structural analysis of large intracontinental wrench faults is fundamental for deciphering the long-term evolution of continental crust in complex areas in terms of their geodynamic evolution and large-scale crustal block displacements. In this contribution, we demonstrate a pre-Miocene dextral activity of the present-day left-lateral Great Kavir - Doruneh Fault System (GKDFS, Central Iran), one of the major intracontinental active strike-slip faults extending from the Afghan border to the Nain region between Central Iran and the Sanandaj-Sirjan Zone. We document important dextral shearing recorded along a segment of the GKDFS, the Arusan Fault System (AFS), located east of Jandaq, close to the present-day active trace of the GKDFS. The AFS include several ENE-WSW striking strands exposed for a length of more than 50 km, which couple pre-Cretaceous ophiolites and metamorphic basement units with the Cretaceous succession of the Khur basin. The fault shows transpressional structures consistent with a dextral shear including thrusts and en échelon folds affecting the Cretaceous carbonate units. Paleostress reconstruction based on mesoscopic fault analysis and related folds geometry allowed to establish vorticity parameters indicating that deformation occurred close to a total simple shear regime with a calculated Wk between 0.9 and 1. The enormous Meso-Cenozoic dextral displacements occurred along the AFS and along the entire GKDFS are attested by the up to several hundreds of kilometers offset of the Paleotethys suture zone, from NE Iran to the western border of Central Iran.

The northern Adamello batholith (European Southern Alps) is crosscut by E-W trending pseudotachylyte-bearing paleoseismic fault zones composed of multiple subparallel fault strands. The main faults are the Gole Strette Fault Zone (GSFZ), here discussed in detail, and the Gole Larghe Fault Zone (GLFZ). The western ending of the GSFZ intersects the propagation of the Gallinera Thrust, a regional structure of Late Cretaceous age, which was truncated and dismembered by the late Eocene - early Oligocene emplacement of the Adamello batholith. Fault slip analysis and paleostress reconstruction suggest that the GSFZ and the Gallinera Thrust were both active during dextral transpression related with Oligocene orogen-parallel shearing along the Periadriatic Fault System. The remnants of the Gallinera Thrusts within the Adamello were reactivated as dextral-reverse faults and do not include pseudotachylytes. The pseudotachylyte-bearing GSFZ show changing structural features from west to east: the fault dip angle decreases from 80° to 45°, the slip vector passes from strike-slip (pitch of 20°) to oblique (pitch of 35° to 45°), and the fault zone thickness increases (> 800 m at the intersection with the GLFZ). The GSFZ is an immature and strong fault as indicated by (i) the local geometry controlled by precursor joints; (ii) the along-strike segmentation; and (iii) the spread of seismogenic faults into kilometre-thick fault zones.

Along the present day central Southern Alps (cSA), evidence of synsedimentary tectonics during the Early Permian are recorded in the Laghi Gemelli Group, which is characterized by the occurrence of abrupt facies variations often associated to coarse-grained deposits. These features are generally attributed to active faults: few works (e. g. Berra et al., 2011) describe local synsedimentary features such as liquefaction or slumping due to seismic shaking, however, further key areas across the Orobic Alps were identified. In particular, we recognized dewatering structures and sedimentary dikes, ball and pillars and small slumps, occurring along hundreds of mesoscopic faults showing meter-scale displacement along high-angle conjugate systems as well as domino-style faults, often accompanied by growth structures. These structures are mainly concentrated in fine-grained sediments of the Pizzo del Diavolo Formation, which was deposited on top of the volcaniclastic succession of the Ca’ Bianca Volcanite and crossed by seismogenic synsedimentary faults. The Permian synsedimentary structures of cSA are mostly associated with high-angle Andersonian normal faults which are combined with low-angle normal faults (LANFs) that developed along the interface between the Permian sedimentary cover and the Variscan basement (Zanchi et al., 2019). LANFs systems are relevant for the Permian hydrothermal circulation, resulting in widespread tourmaline deposition along the fault surfaces and locally in U mineralization. According to our structural analysis, across the central Southern Alps the Permian tectonic setting is characterized by pure extension, dominated by ENE-WSW striking normal faults inverted during the Alpine shortening as high-angle reverse faults (Zanchetta et al., 2015). We point out that an independent tectonic extensional event occurred 80 My after the Permian extension, since the strikes of the Early Permian structure in the considered area are at odds with the Early Ju

Pyroxenites are common compositional heterogeneities in the upper mantle and represent key lithologies in mantle deformation processes, as the local presence of pyroxene-rich compositions can weaken the mantle strength. Pyroxenites occur ubiquitously as variably deformed layers in most of oceanic and orogenic peridotite massifs, and thus can be used as a proxy to investigate the rheological behavior of the mantle in different geodynamic settings, including subduction zones. In the Ulten Zone (Tonale nappe, Eastern Alps, N Italy), numerous peridotite bodies occur within high-grade crustal rocks. Peridotites show a transition from coarse protogranular spinel lherzolites to finer-grained amphibole + garnet peridotites (Obata and Morten, 1987). Pyroxenites veins and dikes, transposed along the peridotite foliation, show a similar evolution from coarse garnet-free websterites to finer-grained garnet clinopyroxenites (Morten and Obata, 1983). This evolution has been interpreted to reflect cooling and pressure increase of pyroxenites and host peridotites from spinel- (1200 °C, 1.3-1.6 GPa) to garnet-facies conditions (850 °C and 2.7 GPa) within the mantle corner flow (Nimis and Morten, 2000). This results in the consequent formation of garnet at the expense of spinel. In particular, garnet initially formed as coronas around spinel and as exsolution lamellae in high-T pyroxenes, and later as neoblasts along the foliation of pyroxenites and host peridotites. Microstructures and crystallographic orientation data indicate that the transition from spinel- to garnet-facies conditions occurred in a deformation regime. Pyroxene porphyroclasts in garnet clinopyroxenites show well-developed crystallographic preferred orientation, high frequency of low-angle misorientations, and non-random distribution of the low-angle misorientation axes. These features indicate that pyroxene porphyroclasts primarily deformed by grain size insensitive (GSI) creep. Core-and-mantle microstructures in

Peridotites and different types of eclogites occurring in the Monte Duria area (Adula-Cima Lunga unit, Central Alps, Italy) share a common eclogite-facies peak at P=2·6-3·0GPa and T=710-750°C, constrained by conventional thermobarometry and thermodynamic modelling. High-pressure minerals are replaced both in peridotites and in eclogites by lower-P and high-T assemblages. In peridotites, the zirconium titanate srilankite occurs asmicrometre-sized crystals in textural equilibriumwith spinel, clinopyroxene and orthopyroxene in kelyphites developed between garnet and olivine. By using a new ZrO2-TiO2 solid-solution model, we provide evidence that srilankite is stable in peridotites relative to zircon+rutile for T > 810°C at an assumed P=0·9GPa, consistent with estimates of T≈850°C (at assumed P=0·9GPa) determined for symplectites made of sapphirine+spinel+Al-rich orthopyroxene+amphibole found in fractures within garnet. In eclogites, kyanite is replaced by symplectites made of anorthite-rich plagioclase+spinel6sapphirine6corundum, formed at T≈850°C and P=0·8-1·0GPa, conditions that are coincident with the high-T overprint observed in the peridotites. Thermodynamic modelling coupled with a material-transfer study provides constraints for these sapphirine-bearing symplectites. In thesemicro-domains, the 'inert' components could not fully equilibrate with the surrounding rock, and the locally high Al content promoted the stability of the Al-rich phases (i.e. mosaic equilibrium). This is the first report from the Alps of eclogite-facies rocks of supposed Alpine age showing a granulite-facies metamorphic overprint, which is, in contrast, well documented in the Variscan belt. On these grounds, although the age of the high-pressure and hightemperature stages in the Monte Duria rocks is still not constrained, the possibility that they reached eclogitic and granulitic conditions in pre-Alpine times should be taken into account.

Vorticity estimates based on porphyroclasts analysis are limited by the extrapolation to three dimensions of two-dimensional data. We describe a 3D approach based on the use of X-ray micro-computed tomography that better reflects the real 3D geometry of the porphyroclasts population. This new approach for kinematic vorticity analysis in the Munsiari Thrust mylonites, the lower boundary of the Main Central Thrust zone (MCTz) in Indian Himalaya, indicates a large pure shear component during non-coaxial shearing. 40Ar/39Ar ages of micas along the mylonitic foliation of the Munsiari and Vaikrita thrusts (the upper boundary of the MCTz) constrain thrust activity to 5–4 and 8–9 Ma, respectively. Available kinematic vorticity analyses of the Vaikrita mylonites suggest the dominance of a simple shear component. Combining these data, we suggest that the southward and structurally downward shift of deformation along the MCTz was accompanied by a progressive increase in the pure shear component in a general shear flow.

In the Monte Duria area (Adula-Cima Lunga unit, Central Alps, N Italy) garnet peridotites occur in direct contact with migmatised orthogneiss (Mt. Duria) and eclogites (Borgo). Both eclogites and ultramafic rocks share a common high pressure (HP) peak at 2.8 GPa and 750 °C and post-peak static equilibration at 0.8–1.0 GPa and 850 °C. Garnet peridotites show abundant amphibole, dolomite, phlogopite and orthopyroxene after olivine, suggesting that they experienced metasomatism by crust-derived agents enriched in SiO2, K2O, CO2 and H2O. Peridotites also display LREE fractionation (LaN/NdN = 2.4) related to LREE-rich amphibole and clinopyroxene grown in equilibrium with garnet, indicating that metasomatism occurred at HP conditions. At Borgo, retrogressed garnet peridotites show low strain domains characterised by garnet compositional layering, cut by a subsequent low-pressure (LP) chlorite foliation, in direct contact with migmatised eclogites. Kfs + Pl + Qz + Cpx interstitial pocket aggregates and Cpx + Kfs thin films around symplectites after omphacite parallel to the Zo + Omp + Grt foliation in the eclogites suggest that they underwent partial melting at HP. The contact between garnet peridotites and eclogites is marked by a tremolitite layer. The same rock also occurs as layers within the peridotite lens, showing a boudinage parallel to the garnet layering of peridotites, flowing in the boudin necks. This clearly indicates that the tremolitite boudins formed when peridotites were in the garnet stability field. Tremolitites also show Phl + Tc + Chl + Tr pseudomorphs after garnet, both crystallised in a static regime postdating the boudins formation, suggesting that they derive from a garnet-bearing precursor. Tremolitites have Mg# > 0.90 and Al2O3 = 2.75 wt% pointing to ultramafic compositions but also show enrichments in SiO2, CaO, and LREE suggesting that they formed after the reaction between the eclogite-derived melt and the garnet peridotite at HP. To test t