Cenozoic intraplate magmatism of central Patagonia, Argentina

Abstract

During Cenozoic times, Patagonia was characterized by an intense magmatic intraplate activity that gave rise to a large volume of basaltic flows and intrusive bodies. This work aims to gather all the available information along with unpublished data of the authors about this magmatism that crops out in the center and south of the Chubut Province, Patagonia Argentina. Small outcrops of Paleocene basalts are present northeast of Paso de Indios and east of Colhué Huapi Lake. The Eocene rocks are represented by basalt flows and intrusive bodies distributed in the west-center, center, and south-west of the Chubut Province. The most significant volume of rocks was produced during the upper Oligocene-lower Miocene generating Meseta Canquel, Sierra Nevada, Sierra De Buen Pasto, and Meseta Los Galpones. Many intrusive gabbroic bodies with different geometries, related to this extended volcanism, crop out in the surroundings of the Colhué Huapi and Musters lakes. The basaltic volcanism of the upper Miocene is represented mainly in the northwest of the Chubut Province. The Pliocene basalts are distributed in the San Bernardo fold and thrust belt. The Pleistocene basalts form volcanic fields of reduced extensions in the north of Chubut, west of Gastre; in the center, near Pampa de Agnia; in the southwest, in the valley of Genoa River and they also form isolated scoria cones located atop Meseta Canquel. Most of the studied rocks have alkaline affinities and OIB signatures, typical of magmas related to garnetiferous peridotite sources. The origin of this basic Paleogene-Pleistocene magmatism, although there are several proposals, would be linked to regional geodynamic processes that include the subduction of mid-ocean ridges with the generation of slab asthenospheric windows and, lithospheric extensional periods related to the steepening of the subducted oceanic lithosphere, as well as a possible relationship with a stagnant oceanic slab at depths of the transition mantle.