CONICET | Buscador de Institutos y Recursos Humanos

The Sierras Pampeanas region of west-central Argentina has long been considered a geologic typeareafor flat-slab induced thick-skinned deformation. Frictional coupling between the horizontalsubducting plate and South American lithosphere from ~12 Ma to the present provides an obviouscausal mechanism for the basement block uplifts that characterize this region. New low temperaturethermochronometry data show basement rocks from the central Sierras Pampeanas (~ longitude 66 ̊W) including Sierras Cadena de Paiman, Velasco and Mazan retain a cooling history of Paleozoic -Mesozoic tectonics events. Results from this study indicate that less than 2 km of basement hasbeen exhumed since at least the Mesozoic. These trends recorded by both apatite fission track (AFT)and apatite helium (AHe) thermochronometry suggest that recent Mio-Pliocene thick-skinneddeformation associated with flat-slab subduction follow inherited zones of weakness from Paleozoicterrane sutures and shear zones and Mesozoic rifting. If a Cenozoic foreland basin exisited in thisregion, its thickness was minimal and was controlled by paleotopography. Pre-Cenozoic cooling agesin these ranges that now reach as high as 4 km imply significant exhumation of basement rocksbefore the advent of flat slab subduction in the mid-late Miocene. It also suggests that thick-skinneddeformation associated with flat slab subduction may at least be facilitated by inherited crustal-scaleweaknesses. At the most, pre-existing zones of weakness may be required in regions of thick-skinneddeformation. Although flat-slab subduction plays an important role in the exhumation of the SierrasPampeanas, it is likely not the sole mechanism responsible for thick-skinned deformation in thisregion. This insight sheds light on the interpretation of modern and ancient regions of thick-skinneddeformation in Cordilleran systems.

enviar mensaje