Reconstructing the thermal and exhumation history of the Sierras Pampeanas through low-temperature thermochronology: A case study from the Sierra de Velasco

STEVENS GODDARD, ANDREA L.; LARROVERE, MARIANO A.; CARRAPA, BARBARA; ACIAR, R. HERNÁN; ALVARADO, PATRICIA

GEOLOGICAL SOCIETY OF AMERICA BULLETIN

GEOLOGICAL SOC AMER, INC

Lugar: Boulder; Año: 2018

0016-7606

The Sierras Pampeanas of Argentina havebeen used as a classic case study to understandthe processes and mechanisms involved inthick-skinned deformation; however, the historyof exhumation and uplift of these rangesremains enigmatic. This study presents newthermochronology and field observationsfrom the Sierra de Velasco, one of the highestrelief (>4 km) and least studied mountainsin the Sierras Pampeanas. Advances in theannealing and diffusion kinetics of the apatitefission track and (U-Th-Sm)/He systemsprovide the tools to interpret a data set witha complex Carboniferous to Miocene coolinghistory. Our results show that rocks sampledacross 2 km of structural depth have experiencedprotracted exposure to temperaturesat or above ~60 °C from ca. 320 to 120 Ma.The well-constrained thermal history allowsus to identify subsequent thermal perturbationsincluding an elevated geothermal gradientduring Cretaceous rifting, late Cretaceous?Paleocene cooling due to isothermalrelaxation and/or exhumation, and acceleratedMiocene exhumation. Quantitativeestimates of the minimum rock overburdensuggest that 1.0 ± 0.8 km of rock has beeneroded from the Sierra de Velasco since theearly Miocene. Although a low geothermalgradient (≤25 °C/km) may support the exhumationof Sierra de Velasco coincident withthe onset of flat-slab subduction in the lateMiocene, we suggest inherited paleotopographyexisted before the Miocene and possiblysince the Paleozoic. Final cooling andexhumation beginning in the early to middleMiocene, concurrent with the onset of flatslab subduction, contributed to the topographyobserved today, but cannot explainthe entirety of the modern relief. We proposethat a history of long-lived topographymay be extrapolated throughout the SierrasPampeanasregion.