1,721,177 research outputs found
Polyphased deformation during uplifting of metamorphic rocks : the example of the deformational history of the Texel Gruppe (Central-Western Austroalpine domain of the Italian Eastern Alps)
No full textMicrostructural control on the P-T path construction in metapelites from the Austroalpine crust (Texel Gruppe, Eastern Alps)
No full textIn the metapelites of the Austroalpine Texel Gruppe a sequence of metamorphic reactions synkinematic with successive regional deformation phases (D1, D2 and D3) can be identified by microstructural analysis and by mapping of structures. The thermobarometric estimates obtained by this method are used to derive a retrograde P-T-relative time of deformation path. Utilizing available radiometric data allows assignment of an Alpine age at least to the D2 and D3 tectonometamorphic stages which represent the uplift of this part of the Austroalpine crust from a depth ≥30 km. -from Autho
From granulites to eclogites in the Sesia zone (Italian Western Alps): a record of the opening and closure of the Piedmont ocean
No full textThe Sesia zone (Italian Western Alps) offers one of the best preserved examples of pre-Alpine basement reactivated, under eclogite facies conditions, during the Alpine orogenesis. A detailed mineralogical study of eclogitized acid and basic granulites, and related amphibolites, is presented. In these rare weak to undeformed rocks microstructural investigations allow three main metamorphic stages to be distinguished. The inferred P-T path is consistent with an uplift of continental crust produced by crustal thinning prior to the subduction of the continental rocks. In the light of the available geochronological constraints we propose to relate the pre-Alpine granulite and post-granulite retrograde evolution to the Permo-Jurassic extensional regime. The complex granulite-eclogite transition is thus regarded as a record of the opening and of the closure of the Piedmont ocean. -from Author
P-T evolutions vs numerical modelling to understand the transition from Paleozoic to early-Mesozoic tectonics in the Alps
No full textPrograde lawsonite during the flow of continental crust in the Alpine subduction : Strain vs. metamorphism partitioning, a field-analysis approach to infer tectonometamorphic evolutions (Sesia-Lanzo Zone, Western Italian Alps)
No full textDetailed mapping of superposed fabrics and their mineral support allows for reconstruction of the tectonometamorphic evolution of the Ivozio Complex, within the inner portion of the Sesia-Lanzo Zone (Western Italian Alps). The resulting evolution is characterized by a multi-stage structural and metamorphic re-equilibration during Alpine subduction, starting from the pre-Alpine igneous association (Amp0 + Cpx0). The prograde associations begin with S1a marked by AmpI + ZoI which pre-date the growth of GrtI (S1b); successive increase in pressure stabilizes a second generation of Amp + Grt (S1c AmpII + ZoI + GrtII). The growth of prograde lawsonite and omphacite occur during S1d (OmpI + Lws + GrtII + AmpII) within lawsonite-bearing eclogites, while S1e is associated with the break-down of lawsonite, producing the association OmpI + Ky + ZoII + GrtII + AmpII (lws-bearing eclogites); S1d-e stages are associated with AmpII + ZoI + GrtII + OmpI in eclogites. The second generation of penetrative foliation (S2), describing the retrograde evolution, is divided into S2a (AmpII + GrtII + Pg + ZoII) and S2b (Chl + AmpIII + Pg + Ab). The comparison between the reconstructed evolution of the Ivozio Complex and P-T paths inferred in the Southern Sesia-Lanzo Zone suggests a non-uniqueness of the Sesia-Lanzo Zone continental crust, during the Alpine subduction
Permian-Triassic magmatism and the tectonothermal evolution of the Austroalpine and South-Alpine lithosphere
No full textPre-Alpine tectono-metamorphic units in the central Southern Alps : structural and metamorphic memory
No full textPercorsi P-T e tempi relativi della deformazione nella crosta Austroalpina dell'Oetztal : l'ortogneiss di Parcines e le sue rocce incassanti
No full textIn the metapelites of the eastern Austroalpine domain, in the Texel Gruppe, polyphasic deformation developed under metamorphic conditions from IT-HP to LT-LP.Thermobarometric estimates inferred after microstructural analysis and minero-chemical investigations have been used to derive a retrograde P-T-relative time of deformation path. The resulting P-T boxes indicate that D1 structures developed at 0.9-1.0 GPa and 640-680°C, D2 at 0.6-0.75 GPa and 550-580°C and D3 at P<0.4GPa and T<550°C
The geodynamic significance of the transition between the Variscan collision metamorphism and the HT Permo-Triassic metamorphism: a numerical modelling
No full textP-T evolution vs numerical modelling : a key to unravel the Paleozoic to early-Mesozoic tectonic evolution of the Alpine area
No full textThe pre-Alpine continental crust of the Alps preserves Permian-Triassic magmatic and high-temperature (HT) metamorphic evolutions, which overprinted records of Variscan subduction and collision-related metamorphism. The occurrence of numerous Variscan eclogites in the pre-Alpine continental crust, presently belonging to different structural domains, indicates that part of the Variscan suture zone occurs in the Alpine belt. The late Variscan evolution took place from 340 to 300 Ma, and therefore the igneous and metamorphic signatures up to Upper Carboniferous may represent the record of the late orogenic evolution. On the contrary, different authors interpreted the HT metamorphism associated with gabbro to granite intrusions younger than 290 Ma as the effect of Permian-Triassic late-orogenic collapse or continental rifting. The goal of this study is to reduce the ambiguity about the geodynamic significance of the Permian-Triassic HT metamorphism and igneous activity in the Alpine continental crust, with the support of numerical modelling of: ocean subduction, continental collision, lithospheric detachment and subsequent gravitational thermal relaxation. Comparison of the model predictions with structural and petrologic data has driven the successive model refinements to improve the fit. The best fit model predictions show a rather good agreement with natural data (coincidence of age, P-T values and rock compositional affinity) up to late-Variscan times. The poor agreement during the Permian-Triassic evolution suggests that, with respect to the thermal state established during the post-collisional gravitational evolution, an additional positive heat anomaly is necessary to induce the thermal state indicated by natural P-T estimates
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