The diversity of basalts from Patagonia at the latitude of the Chile triple junction (46 degrees-47 degrees S). Additional data and implications on the subduction processes

Additional data and implications on the subduction processes. The basalts e xposed around the Lago General Carrera-Buenos Aires display a wide range of chemical compositions. These include: Cretaceous calc-alkaline magmas typi cal of the Andean arc, Eocene to Quaternary intraplate alkali magmas and Qu aternary magmas, the geochemical signature of which shows similarities with those of Chile ridge MORB. Such diversity is related to the evolution of t he subduction processes below Patagonia, starting with a 'normal' subductio n regime, followed by collision-subduction of the active Farallon-Aluk and Chile ridges together with the development of 'asthenospheric windows' duri ng the Eocene and since the Upper Miocene respectively. (C) 2001 Academie d es sciences / Editions scientifiques et medicales Elsevier SAS.