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.

超高压力变质岩提供了一个难得的机会来研究在C的深度处发生的地球过程。大陆碰撞开始时100公里。印度北部的TSO Morari综合体是这些超高压力台中最大，最年轻的综合体之一。这种复合物的规模和青年，再加上过去十年的分析进步，使我们能够在广泛的地理区域收集独特的准确的变质压力，温度，年龄和结构测量。这些空间分布的数据集将使我们能够在竞争模型中区分这种超高压力岩石在大陆碰撞期间如何形成并被挖掘出来。这项工作将通过支持2名博士学位学生和2-6名本科生的定向研究和教育工作来提高科学和美国的兴趣。在博伊西州立大学（Boise State University）的矿物质学和岩石学课程中，每年多达25名地质专业的教育福利，在华盛顿州立大学的结构地质学课上，每年25个地质专业，每年在一般地质班的华盛顿州立大学每年在华盛顿州立大学。博伊西州立大学和华盛顿州立大学都为不寻常的人群提供了高拉丁裔和退伍军人的学生人数。 Co-Pi长期招募当地社区大学的学生，这将使研究结果和教育机会传播给更广泛的区域受众。这两个PI还将在印度瓦迪亚研究所（Wadia Institute）呈现结果，在国际上达到了广泛的国际人口统计学和进步。超高压力形成和发掘的机制在构造中是一个长期存在的问题。根据印度的TSO Morari复合物收集的数据，我们将测试两个重要的假设，这些假设从超高压力变质的热机械模型中得出：1）C中发生了超高压力循环（埋葬至峰值P-T条件，挖掘至〜1 GPA）出现在C中。 5 MYR和2）超高压力岩石被埋葬，挖掘并分配为连贯的床单。具体来说，我们建议回答以下问题：1）在什么时间和在什么压力温度条件下变成了什么压力温度，超高压力变质持续了多长时间？ 2）在什么时候和在什么压力温度条件下发生了过度印刷，而TSO Morari复合物岩石保持热了多长时间？ 3）冷却速度是多少？ 4）在哪种温度范围内发生了与挖掘有关的剪切？ 5）压力 - 温度变形时间路径的空间分布是什么？ 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.压力 - 温度变形时间将从俯冲和挖掘运输方向的极端位于极端的至少8个地方收集。这些路径中的系统沿运输差异将区分超高压力单元是否被变成并将其作为相干纸张（目前假定）或多个或复杂结构进行挖掘。结果将与单一或近端露头中的多个计时仪的UHP变质的多种热机械模型整合在一起，以最大程度地减少地理外推，确定沿摩托车的年龄，并直接比较已发表的热机械模型，并确定何时中间的统计范围，并确定了统计范围的统计范围。值得通过基金会的智力优点和更广泛的影响审查标准来通过评估来支持。