Basement control, sedimentary basin inception and early evolution of the Mesozoic basins in the Patagonian foreland.

Abstract

The Golfo San Jorge basin and other Mesozoic basins occupy extensive areas of the extra-Andean Argentinean Patagonia. These basins initiated and evolved from the Jurassic as rift basins on an igneous-metamorphic and sedimentary Paleozoic basement. Several studies have indicated that basement structures might have influenced their configuration in their initial stages. Based on an updated synthesis of the structures and fabrics of the Paleozoic basement in the Patagonian foreland, and its comparison with fundamental structures of the Mesozoic basins, this work investigates the existence of relations among them, identifying common control types to most of these basins. The comparison suggests that W-E to WNW-ESE structures controlled those basin sectors located near the Atlantic margin, with scarce evidence of basement control. In the Golfo San Jorge basin, basement control can be observed in the thinnest sedimentary sectors on basements, as part of the Río Chico paleo-high. In general, it is possible to establish closer relations with the basement structures towards the continent interior, in the areas with structural reliefs that are currently striking NNW, NW, and WNW. Here, the main structures layout in some of these depocenters could be compared with the direction and vergence of the Paleozoic foliations and shear zones. The lower Paleozoic structures of the Deseado orogen influenced those sectors further from the Atlantic margin of the Deseado basin and, possibly, the San Bernardo fold belt. Northward of the Golfo San Jorge basin,curved orogenic fabrics linked to the Gondwanic structures determine variations in the orientation of the main depocentres of the Cañadón Asfalto basin. Its influence reaches the northern boundary of Patagonia in the Neuquén basin depocenters, located in the Huincul ridge