Magnetic Fabric and Microstructures of Late Paleozoic granitoids from the North

LOPEZ DE LUCHI, M.; RAPALINI, A.E.; TOMEZZOLI R.N.

TECTONOPHYSICS

Elsevier

Año: 2010 vol. I p. 1 - 59

0040-1951

The origin of Patagonia has long called the attention of South American earth scientists. In more recent years a dispute over whether it is an accreted crustal block thatcollided with Gondwana in Paleozoic times or an authochtonous part of South America has taken place. Widespread Late Paleozoic igneous activity in northern Patagonia may provide significant scientific targets to test these hypotheses. As part of a multidisciplinary study, an integrated microstructural and magnetic fabric study was carried out on the Late Carboniferous Yaminué Complex (YC) and the Early Permian Navarrete Plutonic Complex (NPC) exposed in the northeastern corner of the North Patagonian Massif (40.5°S, 67.0°W). Other investigated units are the Late Carboniferous Tardugno Granodiorite (TG), the newly defined Cabeza de Vaca Granite (CVG) and the Late Permian San Martin pluton (SM). Over 300 oriented cores from 60 sites were collected for anisotropy of magnetic susceptibility (AMS) measurements. These were accompanied by a systematic analyses of over 100 petrographic thin sections to characterize the microstructures of the different magmatic units. Combined analyses of AMS and microstructural data permitted to define that the YC, CVG and possibly TG were intruded during a major compressional event associated with top to the SSW thrusting. This event is probably related to a frontal collision of the North Patagonian Massif and the southwestern Gondwana margin. Time constraints are poor but it probably occurred around 300 Ma. The NPC and SM were emplaced after that tectonic event, which must have ended by 281 Ma. Previous magmatic, geochronological and paleomagnetic data that suggest close connection of the North Patagonian Massif with the South American Gondwana blocks during the Paleozoic, can be reconciled with a Late Paleozoic collision by a para-authochthonous North Patagonian Massif that rifted apart from Gondwana at sometime during the Paleozoic to collide again in the Late Carboniferous – Early Permian.