Mesozoic-Cenozoic denudation history of the Patagonian Andes (southern Chile) and its correlation to different subduction processes

Fission track (FT) analysis is applied to assess the Mesozoic and Cenozoic thermal and denudational history of the Patagonian Andes between 44 degrees and 51 degreesS and the geologic and geomorphic response of late Cenozoic subduction of the active Chile rise mid-oceanic spreading center on the ove rriding plate. Seventy-two FT ages from 43 samples are presented. Zircon FT ages indicate fast post intrusion cooling of Cretaceous parts of the Patag onian batholith and previously unreported Miocene magmatic rocks south of 4 8 degreesS. Metamorphic basement rocks to the east of the batholith are con strained as having been deposited and metamorphosed in the early Carbonifer ous and Late Permian. Apatite FT data reveal initiation of accelerated cool ing and denudation at ca. 30 Ma at the western margin of southern continent al South America followed by an up to 200 km eastward migration of the locu s of maximum denudation that ceased at ca. 12-8 Ma at the position of the p resent-day main topographic divide. This migration is proposed to be relate d to either coeval eastward migration of the retroarc deformation, the effe cts of subduction erosion in the overriding plate at the Peru-Chile trench or less likely, shallowing of the angle of subduction. East of the divide, <3 km of denudation has occurred since the Late Cretaceous. Enhanced denuda tion is interpreted to be the result of increased tectonic uplift driven by a large increase in convergence rates at ca. 28-26 Ma that triggered orogr aphically enhanced precipitation on the west side of the Patagonian Andes a llowing increased erosion by fluvial incision and mass transport processes. The actual process of spreading center subduction had remarkably little in fluence on denudation in the upper plate and indeed coincides with a slowdo wn in denudation.