Time constraints for the tectonic evolution of the SW corner of the North Patagonian Massif, Argentina

LÓPEZ DE LUCHI, M.G., CERREDO, M.E., WEMMER, K

Punta del Este, Uruguay

Simposio; Fifth South American Symposium on Isotope Geology; 2006

Universidad de la República del Uruguay

The pre Jurassic basement of the western border of the North Patagonian Massif (NPM) is composed of metamorphic and igneous complexes that range from Devonian to Triassic. In the southwestern areas of the NPM, the metamorphic basement is the Cushamen Formation (CF) whereas the older granitoids were encompassed as the Mamil Choique Granitoids (MCG). This basement is intruded by undeformed Late Permian-Triassic granitic units. Two deformational phases (D1 and D2) accompanied by foliation development (S1 and S2) were distinguished in CF. Peak metamorphism was synchronous with the penetrative main S2 foliation. Two late deformations (D3 and D4) affected both the metamorphic basement and the intrusive units. D2, the deformation that is associated with the peak metamorphic conditions is bracketed between 335-300 Ma. D3 occurred between 272-265 Ma controlling MCG emplacement and affecting both S2 foliation and TT both in a trajectory of decompression. This interval constrains the end of the ductile deformation at upper greenschist facies.. D4 event might be assigned to the Triassic, a time in which the crust of the NPM is at more brittle conditions as documented by the inferred deformation induced resetting of the muscovite age of the fine grained leucogranite that is emplaced in CF. The Late Triassic cooling age of porphyric granitoids intruding CMG indicate that they would be related with the Batolito de la Patagonia Central. Therefore the Early-Middle Permian magmatic event may represent the transition to the regional Late Permian-Triassic extension.