Preserved extensional structures in an inverted Cretaceous rift basin, northwestern Argentina: Outcrop examples and implications for fault reactivation

Abstract

During the Cretaceous-Eocene interval a system of intracontinental rift basins, the Salta group rift, evolved in northwestern Argentina. Individual segments of the rift later suffered different degrees of inversion during Cenozoic shortening. The Tres Cruces subbasin, on the west side of the Eastern Cordillera, was strongly deformed, being now part of a thick-skinned thrust belt with a predominantly N-S structural trend. On its eastern border, tilting due to folding and thrusting and subsequent erosion have produced exceptional outcrops of preserved east-trending extensional structures including half grabens, rollover anticlines, and extensional fault-propagation folds. Farther west, the synrift succession is only intermittently exposed, although the interference of north- and east-trending structures as well as peculiar, dome-shaped anticlines with spur-like extensions suggest that north-and east-trending Cretaceous faults were reactivated, particularly near their intersections. Compilation of published data and analysis of our new data focused on the Salta rift indicates three main factors favoring the contractional reactivation of normal faults: dip angles lower than approximately 60°, especially for faults striking roughly normal to contraction; strikes no closer to the contraction direction than approximately 30°; and low downdip fault curvatures. Occasional dip-slip reactivation of east-trending faults does not match the present and long-term Andean stress regimes and presents an unresolved problem.