Structural and Thermochronological Constraints on the Exhumation of the Chos Malal Fold and Thrust Belt (~37° S)

Abstract

This chapter reviews the evolution of the Chos Malal fold and thrust belt based on structural and thermochronological data. This fold and thrust belt can be divided into an inner-western zone, characterized by exposed basement-involved structures that are inserted in the sedimentary cover and generated a wide region with thin-skinned deformation, and an outer-eastern zone, where blind thrusts, involving basement rocks, produce deformation in the cover restricted to the deformation front where the main hydrocarbon deposits of the region are located. Zircon (U–Th)/He and apatite fission-track cooling ages at the Cordillera del Viento, ranging from 72 to 51 Ma, evidence a period of uplift and exhumation in the inner zone during the Late Cretaceous–Paleocene. These data are in agreement with the notable unconformity and hiatus observed between Paleogene volcanics and Paleozoic basement rocks. The contraction in this zone continued during the Miocene giving rise to most of the thick and thin-skinned structures of the Chos Malal fold and thrust belt, as revealed by apatite fission-track ages between ~15 and 10 Ma. Furthermore, folded volcanic sequences with 40Ar/39Ar ages of ~15 Ma and intrusive rocks with U–Pb ages of 11.5 Ma evidence this compressive episode. The deformation advanced toward the foreland during the Late Miocene, where samples from the basement-involved Las Yeseras–Pampa Tril anticlines show apatite fission-tracks ages of ~9–7 Ma, which led to the uplift and exhumation of the outer zone of the Chos Malal fold and thrust belt.