Thermochronological Evidence for Eocene Deformation in the Southern Patagonian Andes: Linking Orogenesis Along the Patagonian Orocline

Abstract

Thermochronologic results from zircon fission track and (U-Th)/He data collected across the Patagonian batholith, basement and thrust belt of the southern Patagonian Andes between 51°S and 53°S resolves new spatiotemporal patterns of Paleogene rock cooling that allows us to reconstruct deformational and erosional events along- and across-strike. Our study applies a novel modeling strategy, the Path Family Approach, to filter geologically plausible thermal solutions from inverse modeling results for rocks in this study according to a sample's structural and tectonic context. Our results identify minimal cooling and interpreted exhumation of batholith rocks throughout the Paleogene. However, in the western domain we identify synchronous cooling of Jurassic volcaniclastic rocks in the thrust belt both along- and across-strike between 50 and 35 Ma, which we interpret as a period of out-of-sequence deformation that coincides with the start of a distinct period of orogenesis in the Fuegian Andes (54°S). This finding may suggest that the southern Patagonian Andes and Fuegian Andes evolved as a connected orogenic system along the bend of the Patagonian orocline. In the central domain, modeled cooling of thermally reset Cretaceous basinal strata from 60 to 50 Ma corresponds to a well-recognized erosional unconformity in the adjacent Cenozoic foreland depocenter, indicating that contemporaneous exhumation occurred beyond the margins of the basin. Although not diagnostic, exhumation within the orogenic belt, beyond the Cenozoic foreland basin, provides a new regional context to interpret the cause of this regional erosion event. Collectively these results inform the Paleogene tectonic evolution of the orogen.