Exhumation and uplift of the Sierras Pampeanas: preliminary implications from K–Ar fault gouge dating and low-T thermochronology in the Sierra de Comechingones (Argentina)

Abstract

The Sierras Pampeanas in central and northwestern Argentina constitute a distinct morphotectonic feature between 27°S and 33°S. The last stage of uplift and deformation in this area are interpreted to be closely related to the Andean flat-slab subduction of the Nazca plate beneath the South American plate. K-Ar fault gouge dating and low-temperature thermochronology along two transects within the Sierra de Comechingones reveal a minimum age for the onset of brittle deformation about 340 Ma, very low exhumation rates since Late Paleozoic time, as well as a total exhumation of about 2.3 km since the Late Cretaceous. New Ar-Ar ages (7.54-1.91 Ma) of volcanic rocks from the San Luis volcanic belt support the eastward propagation of the flat-slab magmatic front, confirming the onset of flat-slab related deformation in this region at 11.2 Ma. Although low-temperature thermochronology does not clearly constrain the signal of the Andean uplift, it is understood that the current structural relief related to the Comechingones range has been achieved after the exhumation of both fault walls (circa 80-70 Ma).

Post-Caledonian brittle deformation in the Bergen area, West Norway: results from K–Ar illite fault gouge dating

“…The illite crystallinity is a measure of crystallite thickness, but is also influenced by structural distortion, e.g., dependent age spectra (e.g., Pluijm et al, 2001;Solum et al, 2005;Löbens et al, 2011;Bense et al, 2014;Torgersen et al, 2015) that have been explained by two main processes:…”

Exhumation history and landscape evolution of the Sierra de San Luis (Sierras Pampeanas, Argentina) - new insights from low - temperature thermochronological data

“…On the other hand, recent thermochronological studies in other regions of the Sierras Pampeanas near the Sierra de San Luis indicate that exhumation and cooling associated with uplift since the Cenozoic was considerably small (Löbens et al, 2011;Bense et al, 2013;Enkelmann et al, 2014).…”

“…1; Enkelmann et al, 2014), whereas coeval fault activity was recognized for the Sierras de Córdoba (Whitmeyer, 2008) and the Sierra de Comechingones (Löbens et al, 2011) based on Ar/Ar pseudotachyllite and K-Ar fault gouge data, respectively. Permian exhumation and deformation, in turn, is also recorded in other areas of the Sierras Pampeanas (Coughlin et al, 1998;Bense et al, 2013Bense et al, , 2014Sato et al, 2015).…”

“…Thermochronological data which allow a quantitative evaluation of cooling and exhumation of the basement blocks are still scarce in the southeastern Sierras Pampeanas (Jordan et al, 1989;Coughlin et al, 1998;Löbens et al, 2011Löbens et al, , 2013aBense et al, 2013, Dávila andCarter, 2013;Richardson et al, 2013;Enkelmann et al, 2014;Collo et al, 2015). Hence, the evolution of these ranges since the late Paleozoic is still a matter of ongoing debate (e.g., Jordan et al, 1989;Carignano, 1999;Löbens et al, 2011;Dávila and Carter, 2013;Enkelmann et al, 2014;Rabassa et al, 2014).…”

“…Hence, the evolution of these ranges since the late Paleozoic is still a matter of ongoing debate (e.g., Jordan et al, 1989;Carignano, 1999;Löbens et al, 2011;Dávila and Carter, 2013;Enkelmann et al, 2014;Rabassa et al, 2014).…”