Temporal and spatial evolution of the Somún Curá Magmatic Province, Northern Extra-Andean Patagonia, Argentina

Abstract

The Somún Curá Magmatic Province (SCMP) is a Cenozoic volcanic region comprised by several basaltic fields and large central volcanoes located at the Northern Extra-Andean Patagonia, Argentina. The principal volcanic sequences were erupted between the late Eocene and late Miocene, forming the Meseta de Somún Curá, which covers ~30,000 km2 between 40°30′-43°20′S and 65°50′-69°20′W, involving around 1 to 2 × 103 km3 of mafic lavas, and about half that volume of intermediate to silicic lava-pyroclastic associations. The SCMP developed in a back-arc to intraplate tectonic setting over the North Patagonian Massif (NPM), at the time of two major geodynamic events at the western margin of South America: the consumption of the Aluk and the break-up of the Farallón oceanic plates. The magmatism at the studied area is represented by eight volcanic complexes, the Somún Curá Formation flood basalts, and other units related to minor volcanic fields or polygenetic centres. These sequences share intricate stratigraphic relations, which hinder the evolution of the SCMP. To address this issue, an updated compilation of geochronological determinations for the Meseta de Somún Curá region is provided. Its integrated analysis, together with stratigraphic information, allowed the identification of periods of preferential volcanic emission, after which seven constructional phases between late Eocene and late Miocene are proposed. Within these phases, seven pulses of magmatic activity are interpreted for the volcanic complexes emplaced in this area (~38-37 Ma, ~32.5–31 Ma, ~29.5–28 Ma, ~26-24 Ma, ~21–18.5, ~18-15 Ma and ~10.5 Ma), together with four pulses of effusion of flood basalts, represented by the Somún Curá Formation (~32 Ma, ~27-26 Ma, ~26-25 Ma, and ~21.5 Ma). The superposition and recurrence of the magmatic pulses associated with the volcanic complexes and the Somún Curá Formation argue against the application of a "pre-plateau", "plateau" and "post-plateau" scheme, which is revised. The largest volumes of magma associated with the Somún Curá Formation and the volcanic complexes were extruded during the late Oligocene and the early Miocene, respectively. The area of emplacement of the Somún Curá Formation changed over time, defining a roughly counter-clockwise spatial and temporal pattern, starting from the southwest. The magmatic activity recorded by the volcanic complexes from late Eocene to middle Oligocene seems to have concentrated alternatively along NW-SE and NE-SW corridors, and along a N–S belt to the west during the early Miocene. This systematic organization could be related to the reactivation of previous structures, triggered by the kinematic changes in the convergence vector between the Farallón-Nazca Plates and the South American Plate.