Intrerference of folds in the Juramento Valley - Eastern Cordillera (Salta)

Abstract

The structure in the area of the upper valley of Juramento river differs from regions along strike to the north and to the south. The N-S structural fabric associated with the Andean orogeny (Upper Pliocene) is  affected by an important N-S  shortening component which is responsible for a kilometric scale folding interference pattern. These structures are associated with a major oblique strike-slip fault interpreted as a lateral ramp. The displacement along this oblique lateral ramp generated the N-S shortening components responsible of hanging wall complex deformation. Continuous Cretaceous limestone units (Yacoraite Formation) in the middle of the  cover sequence allow the fold geometries to be accurately defined. The two orthogonal fold sets show dome and basin interference pattern. The upper Juramento valley is located in a pronounced structural depression between the north plunging Creston anticline and the southward plunging Castillejo-El Presidio anticline. Both are major strongly curved basement involved folds with the concave side to the west. Here we postulate that the interference pattern mentioned above is formed by fault - propagation folds related to the reactivation of ancient E-W Cretaceous normal faults which interacted with younger N-S striking Andean (Pliocene) faults.