Eo-Alpine HP metamorphism in the Permian intrusives from the steep belt of the central Alps (Languard-Campo nappe and Tonale Series) |
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Authors: | Gazzola Davide Guido Gosso Edoardo Pulcrano |
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Institution: | 1. Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli 34, 20133 Milano, Italy;2. CNR, Centro di Studio per la Geodinamica Alpina e Quaternaria, Via Mangiagalli 34, 20133 Milano, Italy;3. Department of Geology and Petroleum Geology, University of Aberdeen, Meston building. Old Aberdeen, Aberdeen, Scotland, UK |
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Abstract: | AbstractDiorites and granitoids that intruded the Upper Austroalpine units of the central Alps during the Permian display map-pable tectonic imprints and metamorphic transformations that were acquired during the Alpine tectonometamorphic cycle. Superposed heterogeneous deformations interacted with metamorphic re-equilibration stages and created a range of textural types that reflect local deformation gradients: coronitic transformations textures, normally foliated S-tectonites and mylonitic foliations. The three textural types are distinguished on maps recording foliation trajectories of successive deformation phases, which are correlated to the evolution of metamorphic assemblages. Tectonic deformation of Alpine age is represented by three generations of ductile syn-metamorphic structures. The mineral assemblages stable during the first Alpine deformation phase (D1) are AmpII + P1II + white mica, + Zo/Czo + Grt + Qtz ± Mg-Ch1 ± Ilm in metadiorites and P1II + white micaI + Zo/Czo + Grt + AmpII + Qtz ± Ilm/Ttn in metagranitoids; the successive foliations D2a and D2b are defined by greenschist facies minerals. Thermobarometric estimates allow T = 500–600 °C and P = 1.1 ± 0.2 GPa conditions to be determined during D1 and T ≤ 350 °C and P ≤ 0.5 GPa during D2. Relict igneous minerals in metadiorites allow to determine intrusive conditions of T = 879 ± 110 °C and P = 0.4–0.7 GPa. Radiometric ages and P/T ratio of Alpine PmaxTPmax suggest that the inferred P-T-d-t path may represent the thermal state of the initial Alpine subduction stages. © 2000 Éditions scientifiques et médicales Elsevier SAS |
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Keywords: | high-pressure metamorphism Permian intrusives central Alps |
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