Haroldo Vizán

In the southwestern margin of the North Patagonian Massif there is a NW26 SE belt of igneous and metamorphic rocks defining a limit between the North Patagonian Massif and southern Patagonia (including the Deseado Massif), named the
Central Patagonian Igneous Metamorphic Belt (CPIMB). The objective of this paper is to better understand the geodynamic and tectonic processes that generated its rocks and structures. More specifically, explanations are offered for different questions: 1) the aforementioned belt corresponds to a collisional or accretionary orogen? 2) during which geological event it was built? 3) how was the South American plate driftting during that process? 4) why the foliation of the rocks of one of its localities presents a different structural attitude than others? To answer these questions, paleogeographic reconstructions were performed based on paleomagnetic data ranging from ca.415 Ma to ca.305 Ma. Through these reconstructions and considering the middle and upper Paleozoic rocks located in a central area of this deformational belt (the Taquetrén range) and the geological background of several authors, it was possible to separate the processes involved in two tectonic cycles: the Chanic (late Devonian) and the Gondwanan (Carboniferous-Permian) events. The CPIMB presents rocks from an ancient orogen that was built mainly during the Chanic event. In the Taquetrén range the orogenic process would extend between approximately 400 Ma and about 360 Ma. Based on the data of this area, the Chanic orogen collapsed between about 360 Ma and about 330 Ma as the result of an abrupt change in the movement of South America along with all the other continents that constituted Gondwana. From a global geodynamic perspective, it is known that Pangea formed on a mantle superdownwelling, where subduction zones surrounded this supercontinent. This caused magmatic processes in its margins and, in the Taquetrén range, triggered a plutonic emplacement in the old structures of the previous metamorphic rocks of the orogen at
about 315 Ma. In these plutonic rocks, a Gondwanan tectonic event is recorded at about 300 Ma. During this event, a suggested transpressive deformation could have determined the assembly of southern Patagonia with the rest of the lithospheric domains of South America. This tectonic event ended in the central area of CPIMB before the intrusion of non-deformed batholiths during the Permian.