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Título: Permian nappe tectonics and high-grade metamorphism related to Gondwanide Orogeny in northern Patagonia terrane.
Autor(es): González, Pablo Diego
Oriolo, Sebastián
Schulz, Bernhard
Naipauer, Maximiliano
Marcos, Paulo
Sato, Ana María
Varela, Ricardo
Krause, Joachim
Cábana, María Cecilia
Fecha de publicación: 29-mar-2021
Revista: Metamorphic Studies Group Research in Progress Meeting. The Mineralogical Society. Abstract Volume.
Descripción: González, P.D., Oriolo, S., Schulz, B., Naipauer, M., Marcos, P., Sato, A., Varela, R., Krause, J., Cábana, M.C. 2021. Permian nappe tectonics and high-grade metamorphism related to Gondwanide Orogeny in northern Patagonia terrane. Metamorphic Studies Group Research in Progress Meeting. The Mineralogical Society. Abstract Volume, p. 54. Virtual meeting 29-31 March 2021.
Resumen: The focus of this contribution is to characterize a sequential order of deformational structures and associated metamorphic conditions of the igneous-metamorphic basement rocks from northern Patagonia terrane (41°28’30”S-65°40’30”W). Based on field mapping, mesoscopic structures are analysed to evaluate progressive and polyphasic deformation, developed under regional high-grade metamorphism. Three continuous deformational phases are recognized. During D1 phase, the formation of overturned tight F1 folds is associated with penetrative axial plane foliation S1. It exhibits P-T conditions close to the baric peak, and likely represents the progressive metamorphic stage associated with syn-kinematic growth of garnet-kyanite porphyroblasts in meta-pelites. D2 phase is recorded as either shear bands S2 transposition or mylonitic foliation, coeval with polymorphic transformation of kyanite to sillimanite owing to thermal peak. A nappe system related to kilometer scale El Jagüelito ductile shear zone characterizes the large-scale D2 structure of the investigated area. D3 phase is distinguished by refolding of the former fabric and formation of either kink-bands or crenulation cleavage S3 of the S1-S2 foliation planes, under retrogressive metamorphic conditions. The nappe system exhibit a top-to-the S/SW tectonic transport, and the El Jagüelito shear zone served as a right lateral ramp in the exhumation process among D2-D3 events. Petrographic analyses of metamorphic mineral assemblages and reaction textures combined with conventional geothermobarometric estimates and a pseudosection records the pressure-temperature conditions of metamorphism among D1-D3 events. In situ electron probe Th‐U‐Pb monazite dating of 272, 260, and 251 Ma constraints the main tectono-metamorphic event to Late Permian Gondwanide Orogeny. New results combined with existing geological and geochronological constraints allow inferring a clockwise P-T-D-time evolutionary path within the kyanite-sillimanite stability fields. Comprehensive regional comparison of the large-scale structural framework is indicative of an ongoing oblique subduction beneath the proto-Andean margin of Gondwana in the NE direction. This continental subduction and exhumation lasted at least 20 million years, nearly the entire Guadalupian-Lopingian series, producing transpression and metamorphic conditions of amphibolite-to-granulite facies, in medium- to high-pressure regimes, although the studied area occur in a back-arc to intracontinental settings. Geotectonic implications also includes a long-lived tectono-metamorphic history of the El Jagüelito shear zone, which was formed during Early Paleozoic and successively reactivated during Permian and Jurassic times.
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