Investigating tectonic exhumation and hotspot-related landscape evolution with thermo-kinematic modeling, Pioneer Mountains, Idaho

Abstract:

Thermal history modeling provides a means to evaluate how the cooling paths of individual rocks fit into a regional history of tectonic and erosional exhumation. This study integrates a suite of (U-Th)/He apatite and zircon ages using Pecube 3D thermokinematic modeling in order to investigate the transition from tectonics-dominated exhumation to erosion and incision-dominated exhumation in the Pioneer Mountains, Idaho. The study region is centered on the Pioneer metamorphic core complex (PMCC). High-temperature thermochronologic studies of the PMCC have traced tectonic exhumation via brittle-ductile detachment faulting from ~500 °C to 200 °C between 50-33 Ma (Silverberg, 1990; Vogl et al., 2012; McFadden et al., 2015). HeFTy modeling of new ZHe data indicates rapid cooling (~30°C/myr) associated with tectonic exhumation of the PMCC likely ceased between 29-26 Ma. These data are used to establish a baseline for subsequent landscape evolution modeling using Pecube. New and existing AHe dates across the PMCC cluster around 10 Ma (Vogl et al., 2014), coinciding with the timing of the nearest approach of the Yellowstone hotspot. Thermal and flexural uplift associated with the hotspot and subsequent emplacement of dense volcanic material along the Eastern Snake River Plain is thought to have initiated enhanced erosion in the Pioneers and the development of the >1 km of relief observed today. Pecube modeling is used to predict thermochronologic age distributions for a series of landscape evolution scenarios related to the approach of the hotspot. Taking advantage of a spatially distributed sample set, we use the observed AHe ages to test the plausibility of these scenarios and characterize the potential influence of the Yellowstone hotspot on the regional landscape. We also evaluate the possible influence of a regional thermal spike related to the hotspot. Preliminary results suggest a range of landscape evolution scenarios are capable of reproducing the AHe data; however, predicted apatite fission track age distributions vary significantly between these scenarios, suggesting the analysis of fission track data (in progress) will be key for understanding the landscape evolution history of the Pioneers and shedding light on the lasting impact of a continental hotspot on the regional landscape.