CAREER: Refining zircon (U-Th)/He deep-time thermochronology for constraining Neoproterozoic thermal histories

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Low-temperature thermochronology focuses on understanding the thermal histories of rocks in the upper ~10 km of Earth's crust. The suite of thermochronologic techniques has become essential for understanding the timing and rates of rock uplift and erosion in active or geologically young orogenic belts. This project focuses on a particularly promising and emerging area of research in deep-time (i.e. Precambrian) thermal histories. Deep-time thermochronology can be used to constrain the multiple phases of heating and cooling that have occurred over time spans of 100-1000 million years. This project will examine the timing and magnitude of erosion that created the Neoproterozoic-Cambrian Great Unconformity in the midcontinent U.S. with zircon (uranium-thorium)/helium thermochronology. The erosion constraints obtained as part of this project will serve as crucial inputs for investigations of atmosphere-biosphere-lithosphere feedbacks that relate estimates of erosion to 1) the disassembly of the supercontinent Rodinia, 2) potential triggers for snowball Earth glaciations, and 3) the Cambrian explosion in biodiversity. The project will also seek to further refine the temperature sensitivity of the zircon (uranium-thorium)/helium thermochronometer. The project incorporates an outreach and education plan that seeks to instill an appreciation for the concept of deep-time among undergraduates and the public through the use of a world-class resource available at the University of Illinois: the Rare Book and Manuscript Library. This library houses an extensive collection of rare geologic books and manuscripts dating back to the Enlightenment, which will be utilized in exhibits and incorporated into geology courses. These activities will impart a cultural knowledge of the concept of geologic time, foster a deeper appreciation for how Earth scientists think, and allow undergraduate students to engage with pre-modern primary literature to provide historical context and target fundamental questions of their science.This project focuses on advancing deep-time zircon (U-Th)/He thermochronologic methods at a fundamental level and uses these advancements to expand the range of thermal history related problems and questions that researchers can address. Investigations of the radiation damage-He diffusivity relationship in zircon and the kinetics for radiation damage annealing in zircon will help refine the temperature sensitivity of the zircon (U-Th)/He system. This research will advance our knowledge of the damage-diffusivity relationship via step-heating diffusion experiments on Sri Lankan zircon grains over a damage range for which currently only a single data point exists. Raman spectroscopy measurements from a suite of zircon grains with a wide range of radiation damage will be combined with thermal annealing experiments to provide new kinetics on the process of damage annealing in zircon. The advances in zircon (U-Th)/He deep-time thermochronology will help constrain the timing and magnitude of Neoproterozoic exhumation in the midcontinent U.S. through thermal history modeling. These results will be used to assess existing geodynamic models for the formation of the Great Unconformity, each of which predicts a different timing and magnitude of erosion, and thus provide insight into atmosphere-biosphere-lithosphere interactions in deep-time.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.