Abstract

MARQUEZ, Marcelo J. et al. Sierra Grande volcanic center: petrographical and geochemical characterization of the extensional liasic magmatism, northeastern Patagonia. Rev. Asoc. Geol. Argent. [online]. 2011, vol.68, n.4, pp.555-570. ISSN 0004-4822.

The data, interpretations and conclusions obtained from the lithofacial mapping of Marifil Complex, in an area of 400 km2 near Sierra Grande, northeast of Somún Cura Massif, Río Negro province are presented here. intrusive facies (stocks, dykes, sills and domes) and pyroclastic ones (ignimbrites with different extent of welding and tuffs) associated with volcanogenic sedimentites and limestones were indentified. The lithofacies are not homogeneously distributed, the pyroclastic flows dominate in the south, the stocks in the western region and the domes, dykes and sills concentrated in the Sierra Grande. Microscopic analysis show rhyolitic rocks with phenocrysts of sanidine and quartz and subordinate biotite and plagioclase set in a groundmass with different degrees of devitrification. The chemical analyses show rhyolitic and rhyodacitic composition. The N and NNO orientation of the domes, dykes and sills is coincident with the structures of the Paleozoic sedimentary basement and allow interpreting that the emplacement of the Sierra Grande volcanic center was controlled by reactivation of regmatic faults. in this way, we proposed a fisural origin for this volcanism and that the relative sequence of events would have started with the deposition of sedimentary conglomerates and volcanogenic sedimentites, and continued with ignimbrites, sill, tuffs and limestones, stocks and finally domes and dykes.

Keywords : Rhyolitic volcanism; Patagonia; Jurassic; Volcanic lithofacies.

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