T74 Advances and Applications of Thermochronology in Tectonic, Magmatic, Basin, and Geomorphic Studies I

Monday, 10 October 2022
8:00 AM - 12:00 PM
601

WHAT WERE THE DRIVERS OF HINTERLAND EXHUMATION DURING FLAT-SLAB SUBDUCTION IN THE SOUTHERN CENTRAL ANDES? INSIGHTS FROM MULTI-SAMPLE THERMAL HISTORY MODELING USING HEFTY 2.0 AND FETKIN SOFTWARE

Paper number: T74-10
Program: Technical Sessions
Time: 10:05 AM – 10:25 AM

Authors

Abstract

Flat-slab subduction is a cornerstone tectonic process, commonly linked to changes in convergent margin thermal structure, enhanced seismicity, and intraplate shortening and magmatism expressed hundreds of kilometers from the trench. Yet, the impacts of flat-slab subduction on hinterland evolution remain poorly understood. We leverage new thermochronological data from the Argentine Frontal Cordillera (a zone of high hinterland topography above the modern flat-slab segment at 29–33ºS) and novel thermal history modeling techniques to interrogate the influence of (1) increased plate coupling, elevated shortening, and structurally-driven exhumation along emergent or subsurface faults, and/or (2) dynamic uplift associated with slab flattening and inboard migration of the subduction hinge. New apatite and zircon (U-Th)/He data quantify hinterland cooling during Paleogene subduction and Neogene flattening of the Nazca oceanic plate. Our thermal history modeling approach implements a time-elevation extension to the 1D HeFTy thermal history modeling program that allows simultaneous inversion of multiple samples along a structural or topographic profile. This extension enables HeFTy to better approximate transient effects such as isotherm compression during rapid exhumation and the transition from geothermal to elevation gradients, and allows for change in the relative depth among samples (e.g., tilting, folding) during the history within user-defined constraints. Multi-sample modeling results from hinterland sample profiles spanning an along-strike distance of >400 km record rapid exhumational cooling coeval with middle Miocene flattening of the subducted slab, and point to structurally-driven exhumation: along an orogen-scale fault-bend fold anticline at 29–31°S, and emergent faults that exhume west-dipping hanging wall panels at ~31–33°S. We illustrate the resulting structural, topographic, and thermochronological relationships along two reconstructed 2D geological cross sections using thermokinematic modeling (FETKin software). This research demonstrates the utility of multi-sample thermal history modeling in refining the results obtained from single-sample modeling approaches, and evaluating the timing, rates, and drivers of exhumation during changes in subduction.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-381296

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