The Alta Sierra Volcanic Complex, The Youngest Expression of Somún Curá Magmatism. North Patagonia. Argentina

CERREDO, M. E.,; REMESAL, M; PARICA, C.A.

Heidelberg

Congreso; 24th Colloquium on Latin American Earth Sciences; 2017

Universität Heidelberg

The Alta Sierra de Somun Cura Volcanic Complex (ASSCVC) is the northernmost post-plateau assemblage set over the Somún Curá basaltic plateau. The ASSCVC basalt to trachyte assemblage is dominated by basaltic lava flows with subordinated pyroclastic contributions lo-cated at central Río Negro province, within the Oligo-Miocene Somún Curá Magmatic Province. The ASSCVC defines a widespread subalkaline-alkaline trend with minor proportions of under-saturated rocks (Remesal et al. 2016; Maro and Remesal, 2012).Several volcanic buildings make de highest reliefs (1500-1600 m.a.s.l.) of the Complex; these basalt-to-trachyte constructions are arranged along a nearly 25 km-long belt, of NNW-SSE strike set within a low relief volcanic field of basaltic composition and roughly circular outline ( 400 km2). The ASSCVC basaltic rocks belong to distinct chemical groups: subalkaline, transi-tional and alkaline basalts, in addition to minor basanites and foidites. The most differentiated terms, trachytes share the same trend of the alkaline basic group.Presently published geochronological information is restricted to the trachyte facies. K/Ar data of ASSCVC indicate Middle to Late Miocene ( 8-12 Ma) age for the differentiated members of the Complex (Linares 1979; Franchi et al., 2001).We present a new 87Rb/86Sr errochrone built with seven samples (representative of the entire lithologic spectrum of ASSCVC) which yielded a 13.8 ± 8.3 Ma (MSWD=1). This errochrone broadly confirms the Middle to Late Miocene age of the Complex, which clearly distinguish it from the remainder, mostly Early Miocene, complexes within the Somún Curá magmatism. Therefore, a northwards shift of magmatic activity may be confidently inferred for the post-plateau assemblages within the Somún Curá setting.