1,721,026 research outputs found
Microstructures in rocks and rock analogues: EBSD analysis as a key for the understanding of formation processes
No full textMicrostructures are the fingerprints of petrological and deformational processes preserved within rocks, but their understanding may not be straightforward. One way to face this problem is to deform analogue materials under known conditions and to analyze the forming microstructures. Important information on nucleation, growth and deformation mechanisms can be gained from absence or presence of crystallographic preferred orientations (CPOs) of the material forming mineral phases. In the case of existing CPOs, their pattern may suggest important hints regarding activity of slip systems, vorticity, resolved shear stresses, deformation temperature and strain rate. However fully understanding these hidden information may require numerical simulation of the CPOs. The author has chosen to study deformation microstructures by the use of EBSD on natural and synthetic materials, and to simulate formation of CPOs by applying D-Rex on lower crustal rocks and high temperature rock analogues
Single zircon Pb/Pb age constraints on maximum sedimentation ages for quartzphyllite complexes from the Eastern and Southern Alps.
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Simulating the Growth of Garnet Porphyroblasts using a Diffusion-Limited Aggregation Model
No full textThe potential information contained in CPOs: modelling granulite facies quartz pole figures
No full textThe amount of thinning recorded in the Hercynian continental crust exposed in the Serre Massif (Calabria, southern Italy)
No full textHercynian subduction-related processes within the metamorphic continental crust in Calabria (southern Italy)
No full textLinking the deformation history of mylonitized continental rocks to the progress of devolatilization reactions that trigger reaction softening is critical for the understanding of crustal scale processes. We have analysed the field geometries and microstructures of deformed rocks within the southern Hercynian belt in Calabria, as well as modelled the pressure–temperature–deformation (P–T–d) trajectory of a main ductile shear zone that tectonically coupled the deeper crustal Mammola Paragneiss Unit with the upper crustal Stilo–Pazzano Phyllite Unit. P–T modelling of the mylonitic Mammola Paragneiss Unit was performed through calculation of phase equilibrium diagrams with the software thermocalc in the MnNCKFMASHTO model system. The prograde P–T–d trajectory is based on the zoning profiles of garnet porphyroblasts and their mineral inclusions, primarily barroisite and epidote. P–T modelling shows that peak metamorphic conditions of ~0.9 GPa and 585°C were reached during a Dn-1 under-thrusting event. The following exhumation during the Dn mylonitic event, and contact metamorphism during Dn+1 and Dn+2 folding events, have also been modelled because they are essential to restore the previous tectono-metamorphic history. The exhumation trajectory was modelled down to 0.3 GPa with temperatures of 440–460°C, under fluid-deficient conditions, as well as the final late Carboniferous contact metamorphism up to Tmax of 680–720°C. The prograde path shows clear evidence for thermal buffering during garnet growth at the expense of chlorite, with a heating-dominated stage after chlorite breakdown. Subsequently, a rheological change associated with epidote breakdown (i.e. reaction softening) occurred, highlighted by a net steepening of the P/T trajectory towards the pressure peak. On the basis of the barroisite inclusions within garnet porphyroblasts as well as the ‘hairpin’ shape of the reconstructed P–T–d path (before contact metamorphism), we infer that the unusual low T/P gradient for the Hercynian crust exposed in the Mammola Paragneiss Unit records its involvement in the Palaeotethys–Gondwana subduction beneath Laurussia during Dn-1 under-thrusting. We present a new palaeotectonic interpretation along the southern Hercynian belt in Calabria during the Upper Mississippian–Lower Pennsylvanian, that is consistent with previous geochronology studies
Ductile Shearing and Focussed Rejuvenation: Records of High-P (eo-)Alpine Metamorphism in the Variscan Lower Crust (Serre Massif, Calabria—Southern Italy)
Full text linkIn the present study, we unveil the real significance of mylonitic reworking of the polymeta-morphic crystalline basement in the Serre Massif of Calabria (Southern Italy). We use a multidisci-plinary approach to comprehend the structural, microstructural and petrologic changes that occurred along a, so far, not much considered shear zone affecting the Variscan lower crustal rocks. It was never before studied in detail, although some late Cretaceous ages were reported for these mylonites, sug-gesting that this shear zone is of prime importance. Our observations reveal now that the formation of the new structural fabric within the shear zone was accompanied by changes in mineral assem-blages, in a dominant compressive tectonic regime. During this tectono-metamorphic event, high-P mylonitic mineral assemblages were stabilized, consisting of chloritoid, kyanite, staurolite, garnet and paragonite, whereas plagioclase became unstable. Average peak P–T conditions of 1.26–1.1 GPa and 572–626◦C were obtained using THERMOCALC software. These data question (i) that the Serre Massif represents an undisturbed continuous section of the Variscan crust, as generally suggested in the literature, and (ii) highlight the role of (eo-)Alpine high-P tectonics in the Serre Massif, recorded within mylonite zones, where the Variscan basement was completely rejuvenated. © 2022 by the authors. Licensee MDPI, Basel, Switzerland
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