Multi-Mineral Geochronology and REE Geochemistry of High- and Ultrahigh-Pressure Metamorphic Rocks: North Qaidam Terrane, Northwest China

智力上的优点。超高压(UHP)变质作用是大陆俯冲和碰撞的结果。对这种很少露出的岩石的研究可以为大陆碰撞、生长和造山过程以及地壳/地幔相互作用提供新的见解。关于超高压变质作用的一个悬而未决的问题是，这些岩石如何在保持其高P/T矿物组合的同时返回地表。解决这一问题的关键是更好地了解掘尸速度。为了获取这些信息，本项目重点研究了中国柴北山榴辉岩相岩石。锆石、独居石和钛铁矿的U-Pb年代学将与压力、温度和矿物共生作用(基于稀土元素地球化学、矿物包裹体分析和温压分析)相结合，以评估峰期和退变作用的年龄。这些数据将限制与榴辉岩-麻粒岩-和角闪岩相减压相关的折返速率。比率将根据与不同形成压力(深度)相对应的叠加矿物生长带之间的年龄差异(由副锆石和其他相的U-Pb年代学确定)(根据矿物包裹体、稀土元素地球化学和含石榴石矿物组合的温压测定推断)来计算。这项研究可能会极大地促进我们对柴达木地体地质历史的认识，并为超高压折返过程提供新的视角。更广泛的影响。这项研究的核心是与中国同事的合作，从而加强国际科学交流与合作。在我们之前的研究中进行的合作研究已经发表了六篇期刊文章，我们希望继续这种富有成效的合作。在我们之前和继续的工作中开发的微量元素分析程序扩展了最先进的、多用户的斯坦福-USGS SHRIMP-RG设施的能力，从而增强了该设施用于研究和教育的效用。该项目还将为斯坦福大学的研究生和本科生提供培训和研究经验。

Intellectual merit. Ultrahigh-pressure (UHP) metamorphism (i.e., at depths 80 km) is a consequence of continental subduction and collision. Investigation of such rarely exposed rocks can provide new insights into processes of continental collision, growth, and mountain building, as well as crust/mantle interaction. An outstanding question regarding UHP metamorphism concerns how these rocks return to the surface while preserving their high P/T mineral assemblages. Critical to addressing this question is a better understanding of the exhumation rates. To attain such information, this project focuses on well exposed eclogite-facies rocks of the North Qaidam Mountains of China. U-Pb geochronology of zircon, monazite and titanite will be coupled with pressure, temperature, and mineral paragenesis (based on REE geochemistry, mineral inclusion analysis, and thermobarometry) to evaluate ages of peak and retrograde metamorphism. These data will constrain exhumation rates associated with their eclogite- to granulite- and amphibolite-facies decompression. Rates will be calculated based on the age difference (determined by U-Pb geochronology of accessory zircon and other phases) between superposed mineral growth zones corresponding to different pressures (depths) of formation (as inferred from mineral inclusions, REE geochemistry, and thermobarometry of garnet-bearing mineral assemblages). This study is likely to significantly advance our knowledge of the geologic history of the N. Qaidam terrane, and provide new perspectives on UHP exhumation processes in general. Broader impacts. Central to this research is collaboration with Chinese colleagues, thereby enhancing international scientific exchange and cooperation. Collaborative research during our previous research has resulted in six journal publications, and we expect to continue this productive collaboration. The trace element analysis routine developed during our previous and continuing work expands capabilities of the state-of-the-art, multi-user Stanford-USGS SHRIMP-RG facility, thereby enhancing the utility of this facility for research and education. This project will also provide training and research experience for Stanford University graduate and undergraduate students.