Paleomagnetism and geochemistry from the Upper Cretaceous Tres Picos Prieto locality (43ºS), Patagonian Plateau Basalts

Abstract

A paleomagnetic study on nine from lavas from the Upper Cretaceous Tres Picos Prieto locality (43º50'S and 70º3'W), Patagonian Plateau Basaltic Province, revealed that a ca 300 m thick pile of basalts accumulated during three discrete (i.e., temporally separated) volcanic episodes. The chemistry of these lavas shows characteristics compatible with both intraplate and subduction-related magmatism, with the latter having a more important contribution in the younger lavas. Overall, we interpret these rocks to be transitional basalts generated in a suprasubduction environment. The Late Cretaceous to Cenozoic Patagonian Plateau Basaltic Province crops out from eastern Patagonia to the cordillera, and their genesis have been associated to different tectonic processes, even for spatially separated rocks of the same age. Considering that the development of the magmatic province is contemporary with the stage of westward drift of South America, we proposed that magma generation and upwelling due to rapidly shearing asthenosphere inducing circulatory flow associated to asperities in the lithosphere-asthenosphere interface (shear-driven upwelling) can be evaluated as a further potential mechanism to account for many outcrops of these backarc to intraplate lavas.