Cenozoic tectonic inversion and structural vari ations along the Tonco Valley, Valles Calchaquíes – Northwest Argentina

Acta geológica 23 (1-2): 2011

Abstract

The sedimentary cover in the Calchaquí valleys is represented by two sedimentary basins. The oldest corresponds to the Cretaceous rift basin (Cretaceous-Eocene) represented by the S alta Group and the youngest is related to the Andean foreland basin (Eocene-Pliocene) represe nted by the Payogastilla Group. Recently an unconformity has been recorded between the two s edimentary fill basins and growth structures were founded developed in the base of the Pay ogastilla Group that allow us to interpretan Eocene deformation event. Part of the faults rel ated to the growth structures were normal faults during the Cretaceous rift and inverted during the Eocene. The Tonco valley forms part of the Calchaquíes valleys and preserves Salta and Payogastilla groups sedimentary successions in an N-S synclinal structure. The synclin e is bordered by two N-S, retrovergentinverse faults, Calchaquí and Tonco faults, that ha ve been interpreted as Cretaceous riftnormal faults. The main goal of this paper is to pr esent a detailed description of structural variations along the syncline. Two structural directions have been interpreted, the first delineated by the Salta Group and the other by the Payogastilla Group which evidence the unconformity between these Groups. Characteristic struct ural/stratigraphic inversion features are described, and allow us to interpret that the Tonco fault was a normal fault and the Calchaquí fault was a half-graben border during the Cretaceou s and these faults could have been inverted during the Eocene.