Causes of Variable Shortening and Tectonic Subsidence During Changes in Subduction: Insights From Flexural Thermokinematic Modeling of the Neogene Southern Central Andes (28–30°S)

Abstract

The Andes of western Argentina record spatiotemporal variations in morphology, basin geometry, and structural style that correspond with changes in crustal inheritance and convergent margin dynamics. Above the modern Pampean flat-slab subduction segment (27–33°S), retroarc shortening generated a fold-thrust belt and intraforeland basement uplifts that converge north of ∼29°S, providing opportunities to explore the effects of varied deformation and subduction regimes on synorogenic sedimentation. We integrate new detrital zircon U-Pb and apatite (U-Th)/He analyses with sequentially restored, flexurally balanced cross sections and thermokinematic models at ∼28.5–30°S to link deformation with resulting uplift, erosion, and basin accumulation histories. Tectonic subsidence, topographic evolution, and thermochronometric cooling records point to (a) shortening and distal foreland basin accumulation at ∼18–16 Ma, (b) thrust belt migration, changes in sediment provenance, and enhanced flexural subsidence from ∼16 to 9 Ma, (c) intraforeland basement deformation, local flexure, and drainage reorganization at ∼12–7 Ma, and (d) out-of-sequence shortening and exhumation of foreland basin fill by ∼8–2 Ma. Thrust belt kinematics and the reactivation of basement heterogeneities strongly controlled tectonic load configurations and subsidence patterns. Geo/thermochronological data and model results resolve increased shortening and combined thrust belt and intraforeland basement loading in response to ridge collision and Neogene shallowing of the subducted oceanic slab. Finally, this study demonstrates the utility of integrated flexural thermokinematic and erosion modeling for evaluating the geometries, rates, and potential drivers of retroarc deformation and foreland basin evolution during changes in subduction. © 2022. American Geophysical Union. All Rights Reserved.