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.

超高压变质岩提供了一个难得的机会，研究地球的过程中发生的深度c。在大陆碰撞开始时是100公里。位于印度北方的左莫拉里复合体是最大也是最年轻的高压火山之一。这个复杂的规模和年轻，再加上过去十年的分析进展，使我们能够在广泛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。这些空间分布的数据集将使我们能够区分竞争模型，以了解这种高压岩石如何形成，并在大陆碰撞过程中被挖出。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推进科学和美国的利益。额外的教育福利将为博伊西州立大学每年多达25名地质学专业的矿物学和岩石学课程、华盛顿州立大学每年25名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名本科生提供额外的教育福利。州立大学的普通地质学课程。博伊西州立大学和华盛顿州立大学都有大量的拉丁裔和退伍军人学生。Co-PI Long在当地社区学院招募学生，这将使研究成果和教育机会传播给更广泛的区域受众。这两个项目也将在印度瓦迪亚研究所展示成果，以达到广泛的国际人口和推进国际科学。超高压变质岩形成于柯石英稳定场内或上方，并在许多造山带中观察到。超高压岩石的形成和出露机制是构造学中一个长期存在的问题。根据印度Tso Morari杂岩的资料，我们将检验两个重要的超高压变质作用热-力学模型：1）超高压旋回（埋藏至峰值P-T条件，折返至~ 1GPa）发生在c.超高压岩石被埋藏、掘出和侵位为连贯的岩席。具体地说，我们打算回答以下问题：（1）左莫拉里杂岩是在什么时间、什么压温条件下变质的，超高压变质作用持续了多久？2)角闪岩相的叠加是在什么时间和什么压力-温度条件下发生的，左莫拉里杂岩保持热的时间有多长？3)冷却的速度是多少？4)在什么温度范围内会发生与挖掘有关的剪切作用？5)压力-温度-变形-时间路径的空间分布是什么？收集的数据将包括压力-温度条件下使用包体和边缘温压法，Lu-Hf年龄的前100压力石榴石核心和100压力石榴石边缘，U-Pb年龄的任何高U金红石包体，40 Ar/39 Ar年龄的角闪石和白云母，石英c轴张开角测温，和扩散模型的石榴石化学梯度。压力-温度-变形-时间路径将从位于俯冲和折返输送方向上的沿着极端的至少8个地点收集。这些路径的系统性沿程输运差异将区分超高压单元是作为一个连贯的岩席（如目前所假设的）变质和折返，还是作为多个或复杂的结构。结果将与超高压变质作用的各种热-力学模型相结合，在单个或近端露头中使用多个计时器，以尽量减少地理外推，确定沿着和横向走向的年龄，与已发表的热-力学模型进行直接比较，并确定何时中-该奖项反映了NSF的法定使命，并通过使用基金会的学术价值和更广泛的影响审查标准。