Orthogonal folding to the ocloyic deformation trend in pre-Ordovician rocks of the Famatina Sysem

Abstract

This contribution documents a folding episode orthogonal to the ocloyic deformation in the central region of Famatina, involving low-grade metamorphic units considered as part of the Negro Peinado Formation. At the Río El Oro canyon, west of Chilecito, a first folding (P1) with ~E-W fold axis, plunging westward (~250°/20°), an axial plane of ~75°/85°S was recognized. This folding is relatively open (~150m wave length) and shows an associated S₁ penetrative cleavage that affected S₀ bedding. Its orientation indicates a ~N-S shortening direction. Regional P2 folding overprints P1 with a ~N-S fold axis, in coincidence with the traditionally recognized deformation for Famatina. This N-S folding has recently been considered as a Type-0 co-axial superposed folding during the protracted history of ~E-W shortening that affected the region from the Ordovician onwards. Although the orientation of the older relict deformational phase can be the result of local components, due to its regional expression it is suggested that it might relate to a more complex pre-Ordovician subduction history than previously recognized at the western Gondwana margin.