70-2 Exploring geometric and kinematic linkages between fold-thrust belt and basement-involved structural systems in the seismically active Pampean flat-slab segment

Abstract:

The Argentina-Chile (Pampean) flat-slab segment at 32°S poses ideal opportunities to examine the effects of subducted slab flattening on middle- to upper-crustal deformation and related structural interactions in the overriding plate. Connections between deeply rooted, seismogenic faults underlying the Sierra Pie de Palo basement-cored uplift and upper-crustal faults involving sedimentary cover rocks in the Eastern Precordillera remain poorly understood. We integrate thermochronology data, inverse thermal history models, and preliminary flexural kinematic modeling to constrain the timing and magnitude of deformation and investigate potential geometric and kinematic linkages between sedimentary cover- and basement-involved tectonic domains. New apatite (N=9) and zircon (N=4) (U-Th)/He analyses of Paleozoic bedrock within the thin-skinned Precordillera fold-thrust belt, interpreted using inverse thermal history models, reveal sample cooling to <30°C by ~20–40 Ma, followed by protracted residence at near-Earth surface conditions until present day. In contrast, thermal histories from overlying Neogene foreland basin deposits require up to ~60°C of post-depositional burial reheating, followed by structural exhumation and eastward (foreland)-younging cooling from ~18 to 2 Ma. We compare the range of thermal histories permitted by the thermochronology data with thermal pathways predicted by forward flexural thermokinematic models to examine the influence of end-member interpretations on patterns of uplift, exhumation, and subsidence. Preliminary models testing published structural interpretations and in-sequence kinematics failed to replicate the modern topography and bedrock exposure within the Precordillera. However, revisions to incorporate out-of-sequence faulting—including synchronous activity along most Precordillera faults—yielded significantly improved fits to the regional geology and topography while highlighting the sensitivity of model results to deformation kinematics. In addition, our models demonstrate that interpretations of west-directed structural linkages between Sierra Pie de Palo and the Eastern Precordillera would generate ~4 km of Neogene rock uplift and exhumation in Sierra Pie de Palo, conflicting with thermal histories indicated by thermochronology data. Conversely a preliminary east-directed kinematic model that incorporates preferred (out-of-sequence) deformation kinematics successfully replicates modern topography, produces <1 km of basement exhumation in the Sierra Pie de Palo, and yields partially to unreset predicted AHe, AFT, and ZHe ages consistent with thermochronology results. Ongoing flexural thermokinematic models will further validate and refine patterns of structural deformation, exhumation, and heating/cooling based on comparison with geological datasets.

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