EVOLUTION OF THE ANDEAN OROGENIC FRONT SOUTH OF BARILOCHE AREA, ÑIRIHUAU BASIN AND EL MAITÉN BELT (~42ºS).

RAMOS, MIGUEL E.; ORTS, DARÍO; CALATAYUD BASUALDO FELIPE; FOLGUERA, ANDRÉS; RAMOS, VICTOR A.

Heidelberg

Congreso; 22nd International Coloquium onLatin American Earth Sciences; 2011

Universitat Heidelberg

A field study of the Ñirihuau basin, nearby the El Maitén range, between the 42º00´S and the 42º20´S, has revealed new stratigraphic relationships. The structural analysis of this Andean segment, allowed a new interpretation of the tectonic setting of these Patagonian foothills. The stratigraphic sequence consists of four units: The base is represented by the Oligocene Ventana Formation, formed mainly by andesitic volcanic and pyroclastic rocks. The sandstones of the Ñirihuau Formation of ~22-17 Ma rest in general conformably on the previously described volcanic piles (González Bonorino, 1973). Paredes et al. (2009) differentiated a series of lithofacies associations in stratigraphical order in the northern part of this basin. We identified a series of sections, circumscribed to the southern part of the basin that can be compared to the ones described to the north. These sequences are exhumed at the eastern slope of the El Maitén range corresponding to the Cushamen fold and thrust belt. In the western sector an east-verging thick-skinned structure is dismembered by a series of synthetic-to the main thrust front structures, affected by a series of west-verging backthrusts developed in the back limb.