Andean deformation in northern Sierras Pampeanas, NW Argentina

The Sierras Pampeanas of north-central Argentina are basement cored blocks that were exhumed and tilted along high angle reverse faults during the Andean compression. These basement blocks expose >1000 km by ca. 100 km of deformed and metamorphosed turbidites and Lower Paleozoic sedimentary rocks that record major deformational events in the tectonic evolution of the proto-Pacific South American margin. We present combined field, structural, and petrographic data to describe the brittle deformation in the Northern Sierras Pampeanas produced by the flat slab subduction of the Nazca under the South American plate. The flat slab region is characterized by the absence of modern arc volcanism and double verging foreland thrust belts. Structures related to thick-skinned deformation in northern Sierras Pampeanas include folds of variable scales, west-verging imbricated thrust sheets involving Upper-Precambrian to Cambrian through Tertiary rocks, fault bend folds, and kinks associated to the thrust structures. The core of the ranges reveals that bedding and Cambrian folds were affected by a pulsating and continuous deformation associated with a recent compressional event that we associate to the Andean Orogeny. Principal joint systems in the area of study preserve a predominant N-S orientation, suggesting E-W extension. Based on these observations, we propose the existence of an extensional stage in the tectonic evolution of the Andean foreland basin in this region.