Collaborative Research: How do ultrahigh pressure metamorphic sheets form and exhume? A case study from the Tso Morari complex, India

合作研究：超高压变质片如何形成和挖掘？

• 批准号: 2118114
• 负责人: Matthew Kohn
• 金额: $ 34.14万
• 依托单位: Boise State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-06-01 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2118114&HistoricalAwards=false
• 关键词: Collaborative; Research; How; do; ultrahigh

Ultrahigh pressure metamorphic rocks provide a rare opportunity to investigate Earth processes that occur at depths of c. 100 km at the onset of continental collisions. The Tso Morari complex in northern India represents one of the largest and youngest of these ultrahigh pressure terranes. The size and youth of this complex, coupled with analytical advances over the last decade, permit us to collect uniquely precise metamorphic pressures, temperatures, ages, and structural measurements across a wide geographic region. These spatially distributed datasets will allow us to discriminate among competing models for how such ultrahigh pressure rocks form and are exhumed during continental collisions. This work will advance science and US interests by supporting the directed research and education efforts of 2 PhD students and 2-6 undergraduate students. Additional educational benefits will accrue to as many as 25 geology majors per year at Boise State University in mineralogy and petrology classes, 25 geology majors per year at Washington State University in a structural geology class, and 1500 undergraduates per year at Washington State University in general geology classes. Both Boise State and Washington State Universities serve an unusual demographic with high Latino and military veteran student populations. Co-PI Long recruits students at local community colleges, which will allow research results and educational opportunities to be disseminated to a broader regional audience. Both PIs will also present results at the Wadia Institute, India, reaching a broad international demographic and advancing science internationally.Ultrahigh pressure metamorphic rocks form within or above the coesite stability field and are observed in many orogens. The mechanisms by which ultrahigh pressure rocks form and exhume is a long-standing problem in tectonics. Based on data collected from the Tso Morari complex in India, we will test two important hypotheses that derive from thermal-mechanical models of ultrahigh pressure metamorphism: 1) Ultrahigh pressure cycles (burial to peak P-T conditions and exhumation to ~1 GPa) occur in c. 5 Myr, and 2) Ultrahigh pressure rocks are buried, exhumed, and emplaced as coherent sheets. Specifically, we propose to answer the following questions: 1) At what time and at what pressure-temperature conditions were Tso Morari complex rocks metamorphosed, and how long did ultrahigh pressure metamorphism last? 2) At what time and at what pressure-temperature conditions did amphibolite-facies overprinting occur, and how long did the Tso Morari complex rocks remain hot? 3) What was the rate of cooling? 4) Over what temperature range did exhumation-related shearing occur? 5) What is the spatial distribution of pressure-temperature-deformation-time paths? Data collected will include pressure-temperature conditions using inclusion and rim thermobarometry, Lu-Hf ages on pre-ultrahigh pressure garnet cores and ultrahigh pressure garnet rims, U-Pb ages on any high-U rutile inclusions, 40Ar/39Ar ages of hornblende and muscovite, quartz c-axis opening angle thermometry, and diffusion modeling of chemical gradients in garnet. Pressure-temperature-deformation-time paths will be collected from at least 8 localities located at extremes along the subduction and exhumation transport directions. Systematic along-transport differences in these paths will discriminate whether the ultrahigh pressure unit was metamorphosed and exhumed as a coherent sheet (as currently assumed) or as multiple or complex structures. Results will be integrated with diverse thermal-mechanical models of UHP metamorphism using multiple chronometers in single or proximal outcrops to minimize geographic extrapolation, determine ages along- and across-strike, make direct comparisons to published thermal-mechanical models, and identify when mid-crustal emplacement of the Tso Morari complex occurred.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.

超高压变质岩为研究发生在c深度的地球过程提供了难得的机会。大陆碰撞开始时100公里。印度北部的措莫拉里杂岩体是这些超高压地体中最大、最年轻的地体之一。这个复杂的规模和年轻，加上过去十年的分析进步，使我们能够在广阔的地理区域收集独特精确的变质压力、温度、年龄和结构测量结果。这些空间分布的数据集将使我们能够区分这些超高压岩石在大陆碰撞期间如何形成和挖掘的竞争模型。这项工作将通过支持 2 名博士生和 2-6 名本科生的定向研究和教育工作来促进科学和美国的利益。博伊西州立大学每年多达 25 个地质学专业的矿物学和岩石学课程、每年 25 个地质学专业的结构地质学课程以及华盛顿州立大学每年 1500 名本科生将获得额外的教育福利地质课。博伊西州立大学和华盛顿州立大学的学生群体都不同寻常，其中包括大量拉丁裔和退伍军人学生。联合首席研究员 Long 在当地社区学院招收学生，这将使研究成果和教育机会传播给更广泛的地区受众。两位 PI 还将在印度瓦迪亚研究所展示研究结果，影响广泛的国际人口并推动国际科学发展。超高压变质岩形成于柯石英稳定场内部或之上，并在许多造山带中观察到。超高压岩石形成和掘出的机制是构造学中长期存在的问题。根据从印度 Tso Morari 综合体收集的数据，我们将检验源自超高压变质作用热机械模型的两个重要假设：1）超高压循环（埋藏到峰值 P-T 条件并折返到约 1 GPa）发生在c. 5 Myr，以及 2) 超高压岩石被掩埋、挖掘并安置为连贯的薄片。具体来说，我们建议回答以下问题：1）Tso Morari杂岩在什么时间、什么压力-温度条件下发生变质，超高压变质作用持续了多长时间？ 2）角闪岩相叠印是在什么时间、什么压力-温度条件下发生的，Tso Morari杂岩的高温持续了多长时间？ 3) 冷却速率是多少？ 4) 折返相关剪切发生在什么温度范围内？ 5）压力-温度-变形-时间路径的空间分布是什么？收集的数据将包括使用包裹体和边缘温压测定法的压力-温度条件、超高压前石榴石核心和超高压石榴石边缘的 Lu-Hf 年龄、任何高 U 金红石包裹体的 U-Pb 年龄、角闪石的 40Ar/39Ar 年龄和白云母、石英 c 轴张角测温以及石榴石中化学梯度的扩散建模。压力-温度-变形-时间路径将从位于俯冲和折返输送方向极端位置的至少 8 个地点收集。这些路径中系统性的沿传输差异将区分超高压单元是否变形并被挖掘为连贯的片材（如目前假设的）或多重或复杂的结构。结果将与超高压变质作用的各种热机械模型相结合，在单个或近端露头中使用多个计时器，以最大限度地减少地理外推，确定沿和跨冲击的年龄，与已发布的热机械模型进行直接比较，并确定何时中期Tso Morari 复合体发生了地壳就位。该奖项反映了 NSF 的法定使命，并且通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。