THERMAL EVOLUTION OF THE ANDEAN HINTERLAND (ARGENTINA AND CHILE, 30ºS) DURING CHANGING TECTONIC REGIMES: LEVERAGING INNOVATIONS IN MULTI-SAMPLE THERMAL HISTORY MODELING (HEFTY 2)

MACKAMAN-LOFLAND, C.; LOSSADA, A.; FOSDICK, J.; LITVAK, V.; RODRIGUEZ, M.P.; KETCHAM, R.; BERTOA DEL LLANO, M.; HORTON, B.; MESCUA, J.F.; SURIANO, J.; GIAMBIAGI, L.B.; STOCKLI, D.

Pittsburgh

Congreso; GSA Connects 2023; 2023

Geological Society of America

The Andean hinterland of Chile and Argentina (~30ºS) defines a region of voluminous magmatism, polyphase deformation, and high modern topography above a long-lived subduction margin. Construction of this high-elevation domain has been variably attributed to (1) Miocene or earlier internal shortening, (2) crustal thickening and underthrusting during formation of the retroarc fold-thrust belt, and/or (3) lower crustal to sublithospheric processes including lower crustal flow or dynamic uplift associated with Miocene to recent flat-slab subduction. This study integrates new and published geochronology, low-temperature thermochronology, and structural, magmatic, and sedimentological datasets to reconstruct Mesozoic-Cenozoic hinterland evolution and interrogate the potential drivers of uplift-induced exhumation. Our thermal history modeling approach implements the new time-depth extension to HeFTy 2 software, which enables simultaneous inversion of multiple samples along a structural or topographic profile. This extension allows HeFTy to approximate transient effects such as isotherm deflection and the transition from geothermal to elevation gradients and permits change in the relative position among samples (tilting, folding) within user-defined constraints. Single- and multi-sample modeling results based on apatite He and fission track data (AHe, AFT) published along the western Andean flank confirm an Eocene onset of exhumation-driven cooling below at least ~120ºC, while thermal histories derived from new AHe, AFT, and zircon He analyses from the eastern (retroarc) hinterland resolve Mesozoic cooling below ~80–160ºC, protracted residence at temperatures >40–60ºC, and rapid final exhumational cooling initiating in the early Miocene. Multi-sample models further require ~10º top-to-the-east tilting of eastern sample locations, a structural scenario most compatible with hinterland uplift via underthrusting and development of an orogen-scale fault-bend fold kinematically linked to retroarc shortening. This research demonstrates the utility of multi-sample thermal history modeling in improving results obtained from single sample modeling approaches and deciphering the timing, magnitude, and drivers of exhumational cooling during changing geodynamic conditions.