Superimposition of oligo-miocene extensional and contractional basins in the northpatagonian Andean retroarc: The Alumine Basin, Neuquen, Argentina.

Abstract

The Alumine Basin is a volcano-sedimentary depocentre located in the Andean retroarc at 39°S. It is the southern part of a major depositional system: the Bio Bio-Alumine Basin. Stratigraphical, geochronological, sedimentological and structural analysis allow us to conclude that the basin evolved through two stages: an Oligocene extensional stage filled with basalts and reworked volcaniclastic and pyroclastic deposits (Rancahue Formation) and a Miocene contractional stage, filled with alluvial and pyroclastic deposits covered by basaltic lavas (Chimehuin and Tipilihuque formations). The volcanic-rich (basaltic) infill of the extensional stage has a western provenance and was derived from widespread magmatic activity that took place during the Oligocene in the adjacent cordilleran axis. The contractional stage basin is an intramontane depocentre limited by uplifted blocks generated mainly by the inversion of Mesozoic extensional faults. It is strongly asymmetric and shows eastern provenance. Structural and geomorphological evidence indicate the existence of a non-depositional hiatus between the two stages.