Late Cenozoic tectonism and landscape development in the foreland of the Andes: Northern Sierras Pampeanas (26°–28°S), Argentina

Abstract

The Argentine Sierras Pampeanas are reverse fault‐bounded mountain blocks of Precambrian to Paleozoic basement rocks in the foreland of the central Andes. Uplift in the northernmost Sierras Pampeanas fault blocks of Sierra de Quilmes, Sierra Cumbres Calchaquíes, and Sierra Aconquija started about 7 Ma and became pronounced between 4 and 3.4 Ma. The movements culminated after 2.9 Ma, when the conformable Mio/Pliocene Santa María Group was overthrusted, faulted, and folded in the course of principal basement uplift. These movements created climate and base level conditions that resulted in the formation of five pediment levels in the deformed basin strata between 2.5 and 0.3 Ma. Tectonically induced base level changes in the piedmont resulted in three tectonism‐related pediment surfaces between 2.5 and 0.6 Ma, which attest to the neotectonic activity in the Andean foreland. The chronology of young tectonic uplift contradicts models in which early uplift between 20 and 13 Ma is due to the interaction between high topography on the subducting Nazca Plate and the South American craton. In conjunction with the principal uplift of the adjacent Puna Plateau the northernmost Sierras Pampeanas are better explained by E‐W compressional stresses superposed on a thinned lithosphere and inherited zones of structural weakness that facilitated uplift.