Petrografía, geoquímica y edad del complejo volcánico Anecón grande, Paleoceno del macizo norpatagónico

Abstract

This work comprises geological field, petrographic and major, trace and rare earth elements geochemical study of the Anecón Grande Volcanic Complex (AGVC), located in the Río Negro province, south of the Comallo locality (41°00′ – 41°27′ S / 70°22′ – 69°56′ O). From the interpretation of satellite images, field studies and petrographic descriptions three lithological types were identified within the AGVC: basaltic and andesitic lava flows, andesitic to dacitic domes and dikes and pyroclastic rocks of andesitic to rhyolitic composition. The AGVC presents a bimodal composition, a feature shared with rocks from other areas the Pilcaniyeu Volcanic Belt. The composition of the rocks of the AGVC ranges between trachyandesitic basalts (lava flows), dacites, andesites and trachytes (domes and dikes). The rocks of the AGVC have mixt characteristics between subduction and intraplate magmas, as well as the rocks of the Pilcaniyeu Volcanic Belt in other regions. The rocks of the AGVC are more similar to the andean part of the Picaneyeu Volcanic Belt, because they have a stronger subduction signature than the rocks of the extraandean part of the Pilcaniyeu Volcanic Belt. A new U-Pb age in zircon (LA-ICPMS) of 63,6 ± 0,23 Ma (Danian) was obtained for the andesitic domes and dikes of the AGVC. This age places the complex within the early stages of the Pilcaniyeu Volcanic Belt.