PRELIMINARY INVESTIGATION OF FOLD-THRUST BELT–INTRAFORELAND BASEMENT-INVOLVED DEFORMATION USING APATITE (U-Th)/He THERMOCHRONOLOGY DATA AND THERMAL HISTORY MODELING: INSIGHTS FROM THE ARGENTINE PRECORDILLERA AND SIERRAS PAMPEANAS (31–32°S)

The Andean broken foreland of west-central Argentina resides above a modern zone of flat-slab subduction and involves spatially overlapping thin-skinned (e.g., involving sedimentary cover rocks) and crystalline basement-involved deformation accompanied by intense middle- to upper- crustal seismic activity. At 31–32°S, the Andean retroarc and broken foreland region is composed of the thin-skinned, east-directed Central Precordillera fold-thrust belt (CP), the west- directed Eastern Precordillera frontal thrust system (EP), which exposes sedimentary cover rocks but has been variably linked to thin-skinned or basement-involved structural systems, and the basement-involved Sierras Pampeanas (SPs), which partition the distal foreland. Uncertainties persist regarding the timing and magnitude of deformation in these ranges, limiting interpretations of the geometry and kinematic linkages among potentially seismogenic faults. In this presentation, we integrate new and published apatite (U-Th)/He (AHe) thermochronology data from the CP and EP to constrain the timing and magnitude of deformation-induced exhumation, make preliminary geometric and kinematic interpretations, and guide forthcoming fieldwork and sampling targets. AHe thermochronology quantifies the timing of rock cooling below ~40–80°C, and, if cooling can be linked to fault-induced uplift and enhanced erosion, may provide insight into the timing of deformation. A variety of factors (including grain size, radiation damage, zonation, inclusions, He implantation, and grain fragmentation) can influence He date distribution within samples; as some of these factors can be quantified using thermal history modeling, our workflow uses thermal history modeling (HeFTy 2 software) for data visualization, screening, and interpretation based on both single-aliquot and sample mean data. Preliminary results show no major differences in thermal history results based on single grain data vs. central tendency statistics, and demonstrate eastward younging in the timing of exhumational cooling from the CP (>12–7 Ma), to the EP (~8–5 Ma), to the westernmost SPs (< 5 Ma). This spatial pattern in the thermochronology data aligns with an eastward-propagating kinematic model that links uplift and exhumation of the EP with thin-skinned structures accommodating shortening in the CP.