The Alta Sierra de Somún Curá Volcanic Complex, characterization of its basaltic components

REMESAL, M., ; SALANI, F. M.;; CERREDO, M. E., ; CORDENONS, P. D.

Malargüe, Mendoza

Encuentro; 11 Encuentro Internacional Ciencias de la Tierra; 2016

International Center for Earth Sciences, Malargüe

The Alta Sierra de Somún Curá Volcanic Complex (ASSCVC) is a bimodal assemblage dominated by lava flows with subordinated pyroclastic contributions located at the NE area of the Oligo-Miocene Somún Curá Magmatic Province (SCMP), northern Patagonia. The ASSCVC defines a bimodal subalkaline-alkaline trend with a gap between 54 and 58 wt % SiO2, as commonly found within the SCMP. Several bimodal volcanic buildings account for the highest reliefs ( 1500-1600 m.a.s.l.) and are arranged along a nearly 25 km-long belt of NNW-SSE strike over a low relief volcanic field of roughly circular outline (400 km2) of basaltic composition. Both volcanic stages are the subject of our studyThe ASSCVC basalts belong to different chemical series:a) An oldest subalkaline group of basalts and basaltic andesites is found at the base of some volcanic successions in the volcanic field. Some bimodal volcanoes show trachyte-subalkaline basalt assemblages.b) On the basis of their alkalis content within the TAS diagram, a second group of transitional basalts is recognized. This group embodies both subalkaline as alkaline terms, plotting in the basalt, trachybasalt, basaltic andesite and basaltic trachyandesite fields. They mostly occur as spatter cones within the volcanic field and less frequently as part of the bimodal volcanoes.c) Trachybasalt and trachyandesite alkaline rocks occur as eruptive phases or as large lava flows within the volcanic field, in a lesser extent.d) Lastly, sodalite-bearing foidites occur locally, in restricted bulbous effusions, as a minor component in the volcanic field.Such contrasting geochemical compositions among the most undifferentiated terms suggest varying conditions on the genesis of the ASSCVC, which is being studied in grater detail.