MAGNETIC FABRIC AND MICROSTRUCTURES OF LATE PALEOZOIC GRANITOIDS OF THE NE NORTH PATAGONIAN MASSIF, ARGENTINA

Widespread Late Paleozoic magmatism in northern Patagonia is a target to test hypotheses on the origin of Patagonia which has long caught the attention of South American earth scientists. An integrated microstructural and magnetic fabric study was carried out on the Late Carboniferous Yaminué Complex (YC) and Cabeza de Vaca Granite (CVG) and the Early Permian (281Ma) Navarrete Plutonic Complex (NPC), both exposed in the northeastern corner of the North Patagonian Massif (40.5°S, 67.0°W).. Microstructures in the YC are indicative of a transition from magmatic to solid state deformation. The CVG, intrusive in YC, is the most evolved unit and records less intense high-temperature solid state deformation. According to petrologic and structural considerations, the NPC has been subdivided into three facies, i.e. Robaina, Guanacos and Aranda, respectively. Microstructures of the NPC are mostly magmatic to submagmatic, being the Robaina facies the only one that records a more developed high-temperature solid-state overprint when in contact with the YC. Combined analyses of AMS and microstructural data lead us to suggest that the YC and CVG were intruded during a major compressional event associated with top to the SSW thrusting. This event is most likely related to a ca. 300 Ma frontal collision of the North Patagonian Massif and the southwestern Gondwana margin. Emplacement of the NPC post dated this tectonic event. Previous magmatic, geochronological and paleomagnetic data that suggest close Paleozoic connection of the North Patagonian Massif with the South American Gondwana blocks can be reconciled with a Late Paleozoic collision a para-autochthonous North Patagonian Massif that rifted away from Gondwana after the Ordovician and collided again in the Late Carboniferous – Early Permian.