Mechanisms of Subsidence and Uplift of Southern Patagonia and Offshore Basins During Slab Window Formation

DING, XUESONG; DÁVILA, FEDERICO M.; LITHGOW?BERTELLONI, CAROLINA

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS

AMER GEOPHYSICAL UNION

Año: 2023 vol. 24

1525-2027

Subduction of bathymetric anomalies (e.g., an active ridge) can alter the morphology ofsubducted slabs and their coupling to surface processes. A natural laboratory to study these effects is thesubduction of the Oceanic Chilean Ridge beneath the South American plate, which led to the formationof the Patagonian slab window. Its formation and subsequent northward migration contributed to theregression of Patagoniense sea and exhumation of marine strata to their present elevation. To date, there isno quantitative analysis of the effects on the sediment routing system of the slab window. We modeled theNeogene topographic change and foreland sedimentary evolution from the Andean Cordillera to Atlanticmargin. Our results show that subcrustal-driven subsidence correlated with accelerated subduction of theNazca plate is required to explain the timing of the Patagonian transgression and thickness and spatial extent ofmarine beds during the incursion. In other words, traditional mechanisms, such as foreland flexure and globalsea-level rise, are insufficient. The subsequent regression and accumulation of mid-Miocene alluvial-fluvialdeposits were associated with the growth of the Cordillera and a possible flattening of Nazca subduction inthe middle Miocene. Isostatic uplift of ∼1 km due to lithospheric thinning during slab window formationcan explain the foreland exhumation, sediment bypass, and increases in the offshore sedimentation rate.However, spatial-temporal varying dynamic uplift is required to explain the along-strike variations in forelandsedimentation. Our study provides new insights into the interplay between slab window formation, crustaldeformation, and landscape evolution.