Topographic evolution of the Pioneer Mountains (Idaho, USA) in the wake of the Yellowstone hotspot

The track of the Yellowstone hotspot is defined by a series of dated volcanic fields deposited along the Eastern Snake River Plain (ESRP) in southeast Idaho, USA. Bounding this low-lying plain is a crescent of high topography thought to have been produced by thermal uplift in response to the hotspot and/or flexure following emplacement of dense igneous rock in the ESRP. This study investigates the topographic evolution of the Pioneer Mountains, located on the western flank of the ESRP, before, during, and after the closest approach of the hotspot at ~10 Ma. Samples from throughout the mountain range were dated using apatite and zircon (U-Th)/He (AHe, ZHe) and apatite fission track (AFT) low-temperature thermochronology. These data serve as the basis for investigating thermal, tectonic, and landscape evolution using the 3D thermo-kinematic modeling program Pecube. New and existing AHe data (closure temp ~60 °C) span 7-11 Ma and likely reflect exhumation from enhanced erosion accompanying uplift at the closest approach of the hotspot at ~10 Ma. ZHe data (closure temp ~160°C) span 22-30 Ma, and likely reflect the final stages of cooling associated with the tectonic exhumation of the Pioneer metamorphic core complex, which encompasses most of the study area. Core complex deformation is thought to have ceased by ~33 Ma, and we use this time as a baseline for our landscape evolution models. AFT data (closure temp ~100°C) span 7-34 Ma with complex spatial patterns. Our modeling efforts seek to contextualize these patterns within the framework of the known geologic history and, in particular, the changing landscape and thermal structure of the area. Landscape evolution modeling leverages these three thermochronologic datasets to distinguish the low-temperature effects of core complex formation from subsequent exhumation related to landscape evolution. These models are designed to determine how local relief and exhumation rates changed in response to the approach of the hotspot. Preliminary results suggest local relief reached a maximum during the closest approach of the hotspot and subsequently decayed to the topography observed today. Ongoing modeling efforts will further quantify landscape change and investigate the possible influence of a thermal spike during the closest approach of the hotspot.