Exhumation on the Micro to Regional Scale: Case Studies from Central Idaho, USA, and West Antarctica

Abstract

Exhumation is a fundamental geologic process responsible for bringing rock to Earth’s surface from deep underground through tectonic and/or erosional means. This dissertation presents three case studies exploring processes contributing to and/or preserving a record of exhumation on micro to regional scales. Two case studies in the Pioneer Mountains, Idaho, USA, detail a shift in exhumational style from the tectonic exhumation of a metamorphic core complex between 50 – 15 Ma to exhumation driven by landscape evolution in the wake of the Yellowstone hotspot after 15 Ma. Micro-scale structural and geochemical observations are combined using a novel method to track a linked history of deformation and cooling during core complex exhumation. This history is then expanded upon using low-temperature thermochronology and thermo-kinematic modeling, revealing spatial patterns of exhumation related to the end of core complex development and a shift to landscape evolution linked to the approach of the Yellowstone hotspot. The third case study applies these thermochronologic and modeling methods to uncovering the Cenozoic exhumation history of western Marie Byrd Land (MBL), West Antarctica. Models based on bedrock thermochronologic data detail a spatial pattern of exhumation that correlates with uplift of the MBL dome, a ~800 by ~300 km topographic swell thought to be supported by a hot mantle anomaly. Although the limited available bedrock data for western MBL do not record a history of landscape evolution relevant to incision of the West Antarctic Ice Sheet, model predictions of thermochronologic ages across the landscape, including the bottoms of deep glacial troughs, can be compared to age distributions of seafloor detrital material eroded from MBL, providing insight into the magnitude and timing of glacial erosion. Taken together, these case studies characterize exhumation processes on spatial scales covering several orders of magnitude, and the methods and insight presented here serve as a foundation for ongoing investigation of exhumation in Idaho, West Antarctica, and beyond.