What Causes UHT Metamorphism: Lengthscales and Timescales

导致 UHT 变质的原因：长度尺度和时间尺度

• 批准号: 1348003
• 负责人: Bradley Hacker
• 金额: $ 30.46万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-03-01 至 2019-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1348003&HistoricalAwards=false
• 关键词: What; Causes; UHT; Metamorphism; Lengthscales

Crustal rocks that have undergone regional metamorphism at temperatures greater than 900°C are thought provoking; explaining how such high temperatures are attained in the crust is challenging. Central to developing a cogent explanation is quantifying the spatial and temporal scales over which such high temperature prevailed: short spatial and temporal scales imply localized plutonism or fluid flow, whereas long scales indicate larger scale processes. Southern Madagascar represents a key place for studying ultrahigh-temperature metamorphism. There are, however, two key pieces of information missing from our understanding of this otherwise excellent study area: a quantification of how peak temperature varied with depth and with position at a specific depth, and a quantification of how temperature evolved with time. Three endmember hypotheses for the cause of ultrahigh-temperature metamorphism--subduction beneath an arc, collisional thickening and plutonism, and extreme collisional thickening--will be tested using relatively new techniques: titanium-in-zircon, titanium-in-quartz, and zirconium-in-rutile thermometry and pseudosection modeling, in conjunction with laser-ablation split-stream uranium/thorium-lead dates and trace elements of monazite and zircon.Because Southern Madagascar is an archetypal example of exceptionally hot crust, ideas developed there can be applied globally. This proposal is targeted toward understanding how exceptionally hot crust develops, but it will also impact the following questions: What processes are active today beneath hot collision orogens such as Tibet? How do the rheology, topographic, density, and composition of Earth?s crust evolve during collisions? What role did Madagascar play in the evolution of the East African-Antarctica Orogen? These topics are of cross-disciplinary interest in tectonics, petrology, geochronology, geodynamics, geodesy and geophysics. This project brings together scientists from the U.S., Madagascar, Australia, and France. The PIs will interact closely and serve as mentors to each other's students. This provides cross-cultural experiences that ensure that the collaborative impact of this project will be long lasting. This project will provide training and research opportunities for an NSF Graduate Fellow, several undergraduates, and enable us to will continue visiting local elementary schools to expose potential future scientists to Earth science. Continued development of our laser-ablation split-stream technique will benefit the broad range of visitors to our laboratory, the development of laser-ablation systems, and the development of inductively coupled plasma mass spectrometers.

地壳岩石在900℃以上的温度下发生区域变质作用令人深思；解释地壳如何达到如此高的温度具有挑战性。提出令人信服的解释的核心是量化如此高温盛行的空间和时间尺度：短的空间和时间尺度意味着局部的深成作用或流体流动，而长的尺度则表明更大规模的过程。马达加斯加南部是研究超高温变质作用的重要场所。然而，我们对这个原本出色的研究领域的理解缺少两个关键信息：峰值温度如何随深度和特定深度位置变化的量化，以及温度如何随时间演变的量化。超高温变质作用原因的三种端元假说——弧下俯冲、碰撞增厚和深成作用以及极端碰撞增厚——将使用相对较新的技术进行测试：锆石中钛、石英中钛和金红石中锆测温和伪剖面建模，并结合激光烧蚀 分流铀/钍铅年代以及独居石和锆石的微量元素。由于马达加斯加南部是异常炎热地壳的典型例子，因此在那里开发的想法可以在全球范围内应用。该提议旨在了解异常炎热的地壳是如何形成的，但它也会影响以下问题：今天，像西藏这样的热碰撞造山带下面正在活跃哪些过程？碰撞期间地壳的流变、地形、密度和成分如何演变？马达加斯加在东非-南极造山带的演化中发挥了什么作用？这些主题具有构造学、岩石学、地质年代学、地球动力学、大地测量学和地球物理学的跨学科兴趣。该项目汇集了来自美国、马达加斯加、澳大利亚和法国的科学家。 PI 将密切互动并充当彼此学生的导师。这提供了跨文化体验，确保该项目的协作影响将持久。该项目将为一名 NSF 研究生和几名本科生提供培训和研究机会，并使我们能够继续访问当地小学，让未来潜在的科学家接触地球科学。我们的激光烧蚀分流技术的持续发展将使我们实验室的广大参观者、激光烧蚀系统的开发以及电感耦合等离子体质谱仪的开发受益。