Early Paleozoic structural and metamorphic evolution of the Transpatagonian Orogen related to Gondwana assembly.

Abstract

The temporal and spatial relationships between polyphase folding and faulting, regional metamorphism, and granitoids intrusions are discussed for the low-grade basement rocks of the El Jagüelito Formation from the eastern North Patagonian Massif, Argentina, at the inferred western Gondwana margin. As a result of the tectonometamorphic and magmatic events, a late Cambrian-early Ordovician orogenic belt is revealed in northern Patagonia and shall be named the Transpatagonian orogen. It is an NW–SE-trending belt traced from the extra-Andean North Patagonian Cordillera region via the eastern North Patagonian Massif up to the Atlantic coast in the east. The early Paleozoic Transpatagonian orogen is the result of compressional tectonics, also showing a significant dextral shearing, and regional metamorphism leading to the development of a fold-and-thrust belt with an anticlockwise P–T–D-time path. The double-sided orogen is divided into three tectonometamorphic zones bounded by NW–SE trending major faults. Regional comparisons of our results in the present contribution together with available geological data, allow characterizing the orogen as part of a paired metamorphic belt system, with an outboard low-P/high-T belt (northern Patagonia terrane) and a parallel, inboard medium-P/T belt of Barrowian type (Famatinian Orogen on Gondwana margin), respectively. They are juxtaposed tectonically along with the contact of the suture Huincul Fault Zone. The Transpatagonian orogen was implanted along the southernmost Gondwana margin during the final stages of the supercontinent assembly in the early Paleozoic. The tectonism of the Permian Gondwanide orogeny reworked the Transpatagonian orogen.