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

超高压变质岩提供了一个难得的机会来研究在大陆碰撞开始时发生在100公里深处的地球过程。印度北部的措莫拉里复合体是这些超高压地层中最大、最年轻的一个。这个复杂的规模和年龄，加上过去十年分析的进步，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在相互竞争的模型中区分出这种超高压岩石是如何形成的，以及在大陆碰撞期间是如何被挖掘出来的。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。博伊西州立大学每年将招收多达25名矿物学和岩石学专业的学生，华盛顿州立大学每年将招收25名结构地质学专业的学生，华盛顿州立大学每年将招收1500名普通地质学专业的本科生。博伊西州立大学和华盛顿州立大学都有一个不寻常的人口结构，拉丁裔和退伍军人学生人数很多。Co-PI Long在当地社区大学招收学生，这将使研究成果和教育机会能够传播给更广泛的地区受众。这两个pi还将在印度的Wadia研究所展示结果，从而在广泛的国际人口统计和国际上推进科学。超高压变质岩形成于土质稳定场内部或之上，在许多造山带中可见。超高压岩石的形成和演化机制是构造学中一个长期存在的问题。基于从印度Tso Morari杂岩收集的数据，我们将验证来自超高压变质热-力学模型的两个重要假设：1)超高压旋回（埋藏至峰值P-T条件，挖掘至~1 GPa）发生在c. 5 Myr; 2)超高压岩石被埋藏、挖掘和放置为一致的层状。具体而言，我们拟回答以下问题：1)左莫拉里杂岩是在什么时间、什么压力-温度条件下变质的，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，措莫拉里杂岩的高温持续了多长时间？3)冷却速度是多少？4)在什么温度范围内发生了与挖掘相关的剪切？5)压力-温度-变形-时间路径的空间分布是怎样的？收集的数据将包括使用包裹体和边缘热气压计的压力-温度条件，超高压前石榴石岩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，角闪石和白云母的40Ar/39Ar年龄，石英c轴开口角测温，以及石榴石化学梯度的扩散模型。压力-温度-变形-时间路径将从至少8个位置收集，这些位置位于俯冲和掘出运输方向的极端位置。这些路径的系统沿输运差异将区分超高压单元是作为一个连贯的片状物（如目前所假设的）变质和挖掘出来的，还是作为多个或复杂的结构。研究结果将与不同的超高压变质热力学模型相结合，使用多个时计在单个或近端露头中使用，以最大限度地减少地理外推，确定沿走向和跨走向的年龄，与已发表的热力学模型进行直接比较，并确定曹莫拉里杂岩的中地壳侵位发生时间。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.