Late Quaternary fault evolution at the Sierra de Aconquija, Argentina, characterized from 10Be and drone-based topographic data

Quantifying fault evolution in time and space is essential for characterising earthquake hazards and understanding landscape evolution. For a complete picture of Quaternary fault evolution, slip rates calculated from geomorphic strain markers bridge the gap between long-term rates from geological data and contemporary data from seismicity or geodesy. Here, we present a high-resolution record of fault slip rates from the Sierra de Aconquija (SdA), northwest Argentina, based on ¹⁰Be surface exposure dating of boulders and cm-scale topographic data derived from drone-based photogrammetry. Located at the broken foreland of the southern-central Andes, the SdA overlies a transition zone from dipping to flat-slab subduction and therefore provides an opportunity to investigate how complex slab interactions at depth manifest in upper-crustal fault slip. Coalesced alluvial fans have been deposited on the western flank of the SdA, which preserve at least seven aggraded depositional units up to ~300 ka and display scarps associated with east-dipping, range-bounding, reverse faults. We present 55 new cosmogenic ¹⁰Be surface exposure ages from boulders deposited on the fan surfaces. These ages extend an existing fan chronology of 43 ages to cover ~55 km along strike. To measure fault slip, we flew 54 drone surveys to collect photogrammetry data from which we generated 14, centimetre-scale, digital-elevation models using structure-from-motion techniques. Preliminary slip rates span 0.06–2.22 mm/yr. Our data indicate that a fault strand propagated outward from the range front around ~200 ka, which exhibits comparable average slip rates to a parallel strand at the range front. The slowest rates of ~0.06 mm/yr are from the end of this outbound strand and the fastest rates of 1.23–2.22 mm/yr are at the southern end of the Aconquija fault, where deformation is focused on a single range-front strand. Long-term slip rates decrease around a pronounced bend in the fault, suggesting rupture segmentation and ongoing fault linkage. Overall, late Quaternary deformation along the western SdA is evolving both outwards from the range front, and southwards along the range front. This pattern supports existing models of landscape evolution and drainage divide migration linked to Quaternary slip on predominantly east-dipping faults. Ongoing work aims to integrate these findings into a broader context of tectonic and landscape evolution in the Andean foreland.