Plio-Quaternary back arc volcanism of Northern Patagonia

HALLER MJ; MASSAFERRO GI

Reykjavik

Congreso; IAVCEI 2008-General Assembly–Reykjavík; 2008

IAVCEI

A zone of small-volume basaltic lava flow eruptions extends about 350 km inland from the active subuction zone and running parallel to the Andes cordillera for 450 kilometers. North Patagonian eruptions happened mainly 3.8-1.5 million years ago and 1 million years ago. In addition there have been a few eruptions in the Late Pleistocene (0.23 million years ago). Three main types of volcanic centres dominate the Neogene North Patagonian volcanic province: smaller volcanic plateaus formed by coalescence of basaltic shield volcanoes; areally restricted polygenic volcanic complexes and monogenetic volcanos; cinder cones and isolated valley-filling lava flows. Among the younger centres volcanic features of cones and lava flows are well preserved. Compositions erupted are mostly alkali basalts, basanites and trachybasalts. Preliminary trace, isotope and rare elements data are consistent with an asthenospheric mantle source that is chemically similar to sources of OIB and for 20 Ma olivine basalts of the Somuncura plateu. Detectable evidences neither of crustal contamination processes nor of the occurrence of subduction-related components have been found. We suggest that Neogene volcanic activity was driven in Northern Patagonia by incipient rifting of the South American Plate caused by crustal extension.