Links between Mountain Uplift, Climate, and Surface Processes in the Southern Patagonian Andes

Abstract

Miocene surface uplift of the southern Patagonian Andes, related to an episode of rapid plate convergence prior to the ∼14–10 Ma collision of the Chile Ridge with the South American subduction zone, has produced one of the most pronounced orographic rain shadows on Earth. Apatite fission track ages from the western flank of this Andean segment imply that 3–4 km of denudation has occurred in this region since ∼17 Ma. The track-length distribution of the studied samples suggests a complex thermal history with initial cooling followed by reheating, presumably owing to the progressive opening and eastward migration of a slab window after the ridge-trench collision, and ultimately more rapid cooling since ∼4 Ma. These thermochronological data are in good agreement with constraints on the elevation history of the southern Patagonian Andes. Based on sedimentological and geochronological data from ∼23 to ∼14 Ma sedimentary rocks in the eastern foreland, and oxygen isotope data from pedogenic carbonate contained in these deposits, we infer that > 1 km of surface uplift of these mountains occurred between ca. 17 and 14 Ma. Carbon isotope data from the pedogenic carbonate samples demonstrate that this led to strong aridification in the eastern foreland and, presumably, strongly increased precipitation rates on the windward western side of the mountains. Because a thicker trench fill promotes weaker coupling along the plate interface, this implies that progressive surface uplift of the southern Patagonian Andes and the increasing sediment flux to the adjacent segment of the South American trench may have contributed significantly to a decrease in compressive deformation and surface uplift.