The mafic volcanism of Meseta de Coli Toro, Somún Cura massif, Patagonia, Argentina

Abstract

The Meseta de Coli Toro is a mafic volcanic plateau located in the Río Negro province, north of Patagonia, Argentina. It belongs to the Somún Cura Massif geological province and its origin remains uncertain. The previous information concerning the volcanic rocks of Meseta de Coli Toro is limited to field outcrop and petrographic descriptions and one bulk rock geochemical analysis. Based on that information, the lavas were included in the Basalto Meseta Coli Toro unit. This contribution presents new petrographic and geochemical information from three different areas of the plateau: northeastern, central, and western, contributing to the knowledge of the origin and evolution of this volcanic plateau. Most of the studied lava flows classify as alkali basalts with OIB signature. Regarding their petrological features and geochemical signature the lava flows were linked to the Oligocene-Middle Miocene volcanism of the Meseta de Somuncura ´ in northern Patagonia, specifically to the Vulcanitas Corona Chico unit. Based on a published isotope analysis ( 87Sr/86Sr = 0.70439 and 143Nd/144Nd = 0.51275) and the petrological modelling proposed by other authors for the Vulcanitas Corona Chico unit, the lava flows of Basalto Meseta Coli Toro unit derived from 1 to 8% of partial melting of a spinelbearing pyroxenite source, with an isotopic composition equivalent to 96% of DM and 4% of EM1.