DETRITAL THERMOCHRONOLOGY AND GROWTH OF THE CENTRAL ANDES
Cooling ages near the eastern flank show a large range of ages, reflecting variable and locally high erosion rates at the actively uplifting eastern flank. Detrital apatite He ages in single grains from sandstones in the Hornocal syncline range from ~5 to 40 Ma, reflecting both rapid localized erosion, as well as a widespread Eocene cooling event. Similar patterns are seen in other foreland basin sediments recently incorporated into the range (Trimble et al., in press). Detrital zircons show analogous patterns, with ages as young as 15 Ma requiring localized rapid exhumation from ~6-8 km depths. But most zircon He ages are partially or completely unreset, constraining cumulative exhumation to <6-8 km.
Minimum ages for all systems generally increase to the west, consistent with little to no erosion west of the eastern Cordillera and growth of the range through eastward propagation of the retroarc thrust front. However, even in the internally drained, hyperarid core of the range, local topographic highs and inverted Cenozoic basin must erode to depths of no more than ~2 km, to produce reset detrital apatite He ages. Eo-Oligocene basinal sediments in the Cordillera de Domeyko contain first cycle and clearly unreset detrital zircons with U/Pb and He ages ranging from 50 Ma to 220 Ma, but detrital apatite He ages are 20-22 Ma, much younger than depositional age, requiring localized exhumation to no more than ~2 km.
At the large scale, cooling ages across the central Andes are most consistent with focused exhumation to less than ~6-8 km at rates of ~0.3-0.8 km/Myr in a ~150-km wide swath of high precipitation at the eastern front, caused by horizontal accretion and propagation rates of about 5-7 km/Myr. Erosion in the range interior is limited to <1-2 km depths in local topographic highs and inverted basins.