Pre-Andean deformation and its influence on the shortening of the Southern Precordillera, Mendoza, Argentina

Abstract

Andean structures preserve evidence of previous periods of deformation along the proto-Pacific margin of Gondwana. Particularly, the Southern Precordillera, in the southern Central Andes, presents a combination of different structural domains and a double vergence related to the reactivation of pre-Andean structures. This combination and the superposition of deformational events make it difficult to understand the stratigraphic systems and the evolution of the region. This contribution presents detailed information about the structures and evolution of the Southern sector of the Precordillera, focusing on the control exerted by Paleozoic structures over the recent Andean deformation, and the deformational styles of this fold-and-thrust belt. Three main structural domains are recognized. The western domain is characterized by high-angle back-thrusts that concentrate the highest amount of uplift. The central domain is composed of reverse double-vergence faults, and high-angle strike-slip faults. The eastern domain is characterized by pure contractional deformation and only east-verging structures. Four deformational events are recorded and analyzed along the Southern Precordillera at 32°30′S: (1) an Early Paleozoic compressional event, (2) a Late Paleozoic compressional event, (3) a Triassic extensional event, and (4) the Cenozoic Andean compressional event. Our model for the Cenozoic deformation of the Southern Precordillera is restricted to three stages of deformation. During the first stage, Paleozoic west-verging faults are reactivated. The second stage implies reactivation of Paleozoic and Permian-Triassic structures and the generation of reverse Andean faults. The final stage consists of the generation of NE-SW Andean thrusts.