Tectonic and Geodynamic Controls on the Neogene Landscape Evolution of Southern Patagonia

DING, XUESONG; DÁVILA, FEDERICO M.; LITHGOW-BERTELLONI, C

Chicago

Congreso; American Geophysical Union Fall Meeting; 2022

AGU

The subduction of the Oceanic Chilean Ridge under the South American plate since Early-Middle Miocene led to the formation of the Patagonian slab window. Its formation and subsequent northward migration have affected the Andean orogenic deformation and sediment routing from the Cordillera to retroarc foreland basins and ultimately to distal offshore basins. Previous studies that model the evolution of southern Patagonia focus either on one segment of the system (e.g., the foreland) or restrict the time period of study. In this work, we use a source-to-sink landscape evolution code (Badlands) to model the whole system from the Andes to the Atlantic margin over the entire Neogene, spanning both the Oligo-Miocene marine transgression and the present-day slab window stage. We aim to unravel which geodynamic/tectonic scenario of exhumation of the Southern Andean belt explains sedimentation in the Patagonian foreland and offshore basins. Our modeling results show that, in addition to foreland flexural accommodation and sea-level rise, subcrustal-driven subsidence across all of Patagonia is required to explain the timing of the Patagonian transgression and the thickness and spatial extent of marine beds during the incursion. The effects of dynamic (mantle flow driven) subsidence can be correlated with changes in Nazca plate subduction. Its magnitude varies between 150-200 m, depending on the imposed global sea-level curve. The subsequent regression and accumulation of Miocene alluvial-fluvial deposits were associated with the growth of the Cordillera. However, an additional sub-lithospheric force is likely required to reproduce the marine regression. Finally, isostatic uplift due to lithospheric thinning or dynamic topography accompanying slab window formation could explain the foreland uplift, sediment bypass, and increases in offshore sedimentation rate. Reported tilted river terraces require either a spatially varying isostatic uplift or a migrating wave of dynamic uplift.