Abstract

The basalts exposed around the Lago General Carrera-Buenos Aires display a wide range of chemical compositions. These include: Cretaceous calc-alkaline magmas typical of the Andean arc, Eocene to Quaternary intraplate alkali magmas and Quaternary magmas, the geochemical signature of which shows similarities with those of Chile ridge MORB. Such diversity is related to the evolution of the subduction processes below Patagonia, starting with a 'normal' subduction regime, followed by collision-subduction of the active Farallon-Aluk and Chile ridges together with the development of 'asthenospheric windows' during the Eocene and since the Upper Miocene respectively. © 2001 Académie des sciences /Éditions scientifiques et médicales Elsevier SAS.