Pre-Cenozoic brittle deformation in the southern Central Andes: K-Ar Illite dating of fault gouge suggest pre-straining of crust in the region of the Andean Plateau and Eastern Cordillera

In the Andes, reactivated inherited crustal faults play a key role in influencing regional tectonic styles and the areal extent of deformation. Determining the timing of fault activity is essential to reconstruct the sequence of deformation events and their implications for the orogenic evolution of the region. To investigate the history of brittle deformation prior to Cenozoic compressional reactivation in the southern Andean Plateau (Puna), we applied K-Ar illite dating to fault gouges. This method provides insights into the cooling and deformation history of fault systems, offering valuable temporal constraints on tectonic processes. Our study yielded 12 ages from 4 samples, ranging from 299.4 Ma to 122.3 Ma. We interpret these results to document the onset of brittle deformation in the realm of the future southern plateau during the Permian and an early Cretaceous event in the adjacent region where the thick-skinned Eastern Cordillera later evolved during Cenozoic mountain building.