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

高压和超高压变质岩的多矿物年代学和稀土地球化学：中国西北柴达木地体

• 批准号: 0710927
• 负责人: Dennis Bird
• 金额: $ 17.96万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-01 至 2010-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0710927&HistoricalAwards=false
• 关键词: Multi; Mineral; Geochronology; REE; Geochemistry

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.

智力上的优点。超高压（UHP）变质作用（即，深度80公里）是大陆俯冲和碰撞的结果。对这些很少暴露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，这些岩石如何返回到地表，同时保留其高P/T矿物组合。解决这一问题的关键是更好地了解挖掘率。为了获得这些信息，本项目的重点是中国柴北缘的榴辉岩相岩石。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（基于稀土元素地球化学、矿物包裹体分析和热压法）相结合，以评估峰期和退变质作用的年龄。 这些数据将限制与榴辉岩-麻粒岩相和角闪岩相减压有关的折返速率。将根据与不同形成压力（深度）对应的叠加矿物生长带之间的年龄差（通过副锆石和其他相的U-Pb地质年代学确定）（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热压测定法推断）计算速率。这项研究可能会大大推进我们对北大西洋的地质历史的认识。柴达木盆地超高压折返过程的研究提供了新的视角。更广泛的影响。这项研究的核心是与中国同事合作，从而加强国际科学交流与合作。在我们以前的研究中，合作研究已经在六个期刊上发表，我们希望继续这种富有成效的合作。在我们以前和持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Stanford-USGS SHRIMP-RG设施的能力，从而提高了该设施在研究和教育方面的实用性。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。