Early Cretaceous to Cenozoic Growth of the Patagonian Andes as Revealed by Low-Temperature Thermochronology

Abstract

The Southern Patagonian Andes at the latitude of the Chile Triple junction in Argentina and Chile (46°–47.5°S) are the object of an ongoing discussion regarding their orogenic evolution in terms of tectonic crustal thickening and exhumation. Recent works point to an Early Cretaceous onset of shortening according to observations in foreland sequences. The ensuing Cenozoic thermal history of the region was influenced by increased shortening, oceanic-ridge collision and formation of asthenospheric windows in a dynamic subduction setting. Furthermore, the onset of Patagonian glaciations after 7 Ma added increased complexities to the analysis of the main drivers of crustal cooling in this region. We applied zircon (U-Th)/He and apatite fission track thermochronometry, and inverse thermal modeling to unravel the thermal history throughout different structural domains of the Patagonian Andes. New thermochronological data and thermal models showed a previously unrecognized set of Cretaceous cooling ages (120-80 Ma) toward the foreland, that we relate to the onset of contraction during initial tectonic inversion. Toward the hinterland, Cenozoic cooling ages predominate, and are related to Oligocene-Miocene contraction in response to increased subduction velocities. Based on the regional distribution of thermochronological ages and on results from thermal modeling, a resetting of the zircon (U-Th)/He and apatite fission track systems in response to crustal heating related to the formation of an asthenospheric window after 16 Ma appears unlikely. After 7 Ma cooling rates increased in response to enhanced glacial erosion.