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

低温热年代学的重点是了解地壳上~10公里岩石的热历史。热年代学技术套件对于了解活跃或地质年轻造山带中岩石隆起和侵蚀的时间和速率至关重要。该项目侧重于深时（即前寒武纪）热史研究中一个特别有前途和新兴的领域。深时热年代学可以用来约束在100-10亿年的时间跨度内发生的加热和冷却的多个阶段。该项目将用锆石（铀钍）/氦热年代学研究在美国大陆中部形成新元古代-寒武纪大不整合的侵蚀时间和程度。作为该项目的一部分，获得的侵蚀约束条件将作为研究大气-生物圈-岩石圈反馈的关键输入，这些反馈与1)罗迪尼亚超大陆的解体，2)雪球地球冰川的潜在触发因素，以及3)寒武纪生物多样性大爆发有关。该项目还将寻求进一步改进锆石（铀钍）/氦温度计的温度灵敏度。该项目包括一个推广和教育计划，旨在通过使用伊利诺伊大学的世界一流资源：珍本图书和手稿图书馆，向本科生和公众灌输对深度时间概念的欣赏。该图书馆收藏了大量可追溯到启蒙运动时期的稀有地质书籍和手稿，这些书籍和手稿将用于展览和地质学课程。这些活动将传授地质时间概念的文化知识，培养对地球科学家如何思考的更深层次的理解，并允许本科生参与到前现代的原始文献中，以提供历史背景和针对他们科学的基本问题。该项目致力于在基础水平上推进深时锆石(U-Th)/He热年代学方法，并利用这些进步来扩大研究人员可以解决的热历史相关问题和问题的范围。研究锆石中辐射损伤-He扩散率关系以及锆石辐射损伤退火动力学有助于改进锆石(U-Th)/He体系的温度敏感性。这项研究将通过斯里兰卡锆石颗粒的阶梯加热扩散实验提高我们对损伤-扩散关系的认识，目前只有一个数据点存在。对一组具有广泛辐射损伤的锆石颗粒进行拉曼光谱测量，并将其与热退火实验相结合，为锆石损伤退火过程提供新的动力学研究。锆石(U-Th)/He深时热年代学的进展将有助于通过热历史模拟来限制美国大陆中部新元古代发掘的时间和规模。这些结果将用于评估大不整合形成的现有地球动力学模型，每个模型都预测了不同的侵蚀时间和程度，从而深入了解大气-生物圈-岩石圈的相互作用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.