Preliminary K-Ar geochronology of Neogene back arc volcanism in Northern Patagonia, Argentina

HALLER, MIGUEL J., PÉCSKAY, Z., NÉMETH, K., GMÉLING, K., MASSAFERRO, G., MEISTER, C. AND NULLO, F.

Malargue, Mendoza

Conferencia; Third International Maar Conference; 2009

IAVCEI

Obtained K-Ar radiometric ages on back arc basalts in Northern Patagonia allow to distinguish at least two magmatic events forming monogenetic scoria cone- and lava flow field-dominated volcanism. The oldest one (23 – 19 My) is related to the post plateau effusive event of the large Somuncura and Canquel plateaus (Mahlburg Kay et al., 2006), while the youngest (5-1 My) is characteristically originated small-volume basaltic lava flow eruptions aligned in a 450 km long belt parallel to the Andes cordillera about 350 km inland from the present active subduction zone. 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 My old olivine basalts of the Somuncura plateu. Detectable evidences neither of crustal contamination processes nor of the occurrence of subduction-related components have been found so far