Timing of uplift in the Argentine Frontal Cordillera (34-32.5°S), through (U-Th)/He Thermochronology

We use the apatite (U-Th)/He low temperature thermochronometer to study the rock uplift history in the Frontal Cordillera of Argentina between 32.5-34°S, where an abrupt transition in the subduction angle of the Nazca Plate occurs. The Andes in our study area are composed of three major physiographic and tectonic provinces, which have been uplifted as the deformation front stepped eastward over the last 20 Ma. From west to east they are the Principal Cordillera, Frontal Cordillera and Precordillera. The thin-skinned Aconcagua fold-thrust-belt, which today comprises the Principal Cordillera was active between ~20-8 Ma. The thick-skinned Frontal Cordillera began uplifting around 9 Ma. Finally, in the northern part of the study area, uplift and deformation of the Precordillera commenced between 5-2 Ma. South of 33°S, in the absence of the Precordillera, the total amount of crustal shortening is half that of the north, despite similar average and peak range elevations. Remnants of a regionally extensive paleolandscape are preserved in both areas. Two age-elevation profiles were collected from the granitic Permo-Triassic Choiyoi Group in the headwaters of the Rio Tunuyán (south of 33°S) and Rio Mendoza (north of 33°S). In the Tunyán area, 7 samples were collected between 2600 and 4500 m, with paleolandscape remnants at an elevation of ~5000 m. Total local relief in the Río Mendoza sampling area is 2800 m, from which the lower 1400 m were sampled between elevations of 2100 and 3500 m. We aim to constrain 1) the timing of the initiation of deformation-related exhumation of the proximal foredeep associated with the Aconcagua fold and thrust belt and 2) the rate of rock uplift induced river incision of the Rio Mendoza and Rio Tunyán as a proxy for surface uplift.