CAREER: Developing noble gases as tracers of metamorphic dehydration

职业：开发惰性气体作为变质脱水的示踪剂

• 批准号: 2047024
• 负责人: Andrew Smye
• 金额: $ 63.56万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-01 至 2026-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2047024&HistoricalAwards=false
• 关键词: CAREER; Developing; noble; gases; tracers

The habitability of Earth is controlled by the distribution of volatile elements (e.g. water, carbon dioxide) between surface (atmosphere + hydrosphere) and interior reservoirs (mantle + core). Metamorphism during burial and heating of oceanic plates at subduction zones regulates the supply of water into the Earth’s mantle, critically affecting how the mantle flows. However, the specific pathways and fluxes by which water is transported beyond arc volcanoes are uncertain. While direct tracing of subducted water is made difficult by its small number of isotopes, the noble gases are elementally- and isotopically-rich, are fractionated by physical processes and are ideal tracers for the movement of metamorphic fluids. Application of the noble gases as tracers of the deep water cycle requires development of a linkage between noble gas composition and the magnitudes of water loss during subduction. This project will result in a systematic characterisation of the distribution and composition of noble gas isotopes in ancient samples of subducted oceanic crust, establishing the framework for noble gases to be used as tracers of metamorphic fluids. The integrated research and education program proposed here will result in: 1) quantification of the key physical processes that control subduction-processing of volatiles; 2) career-enhancement for an early career scientist and a graduate student, and 3) broadened participation and enhanced diversity in petrological research via a series of formative research institutes targeting applicants from minority-serving institutions.Earth's upper mantle contains an indelible elemental abundance pattern of heavy noble gases (Ar, Kr, Xe) that is strikingly similar to seawater. Because this is a unique composition in the solar system, the only credible explanation is that a non-disrupted, seawater-like noble gas signature survives the subduction process, generally thought to exclude more than 95% of input volatiles. Given that the noble gases are between 100 and 100,000 times more soluble in fluids than crustal minerals, even minor amounts of phase separation during release and transport of metamorphic fluids will fractionate the noble gas composition of subducting rock. How, then, do noble gases escape removal and significant fractionation during subduction? And, can the noble gases be used to quantitatively trace the subduction of water? This project will address these questions through the integration of noble gas compositions, mineralogically-bound H2O contents and thermodynamic estimates of pressure and temperature from exhumed subduction-related rocks. The proposed research will systematically test the overarching hypothesis that noble gas composition is principally controlled by the extent of metamorphic dehydration during subduction. At the core of the educational component of this CAREER program is the development and implementation of a series of summer institutes dedicated to enhancing diversity in petrological research. This program will result in the petrological training of a cohort of undergraduates, many of whom will come from minority-serving institutions. Petrological and geochemical datasets collected as part of the proposed research program will be used to nurture interest, and increase comprehension of undergraduate students, from a diverse array of institutions and backgrounds, in metamorphic petrology.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.

地球的可居住性受挥发性元素（如水、二氧化碳）在地表（大气层+水圈）和内部储层（地幔+地核）之间的分布控制。俯冲带洋板块埋藏和加热期间的变质作用调节了水向地幔的供应，严重影响了地幔的流动。然而，水被输送到弧火山之外的具体途径和通量尚不确定。虽然直接追踪俯冲水是困难的，因为它的同位素数量很少，稀有气体是元素和同位素丰富，通过物理过程分馏，是变质流体运动的理想示踪剂。应用惰性气体作为深水循环的示踪剂，需要建立惰性气体成分与俯冲过程中失水量之间的联系。这一项目将导致对俯冲洋壳古代样品中惰性气体同位素的分布和组成进行系统的定性，建立惰性气体用作变质流体示踪剂的框架。本文提出的综合研究和教育计划将导致：1）控制挥发物俯冲加工的关键物理过程的量化; 2）为早期职业科学家和研究生提供职业提升，3）通过一系列针对少数民族申请者的形成性研究机构，扩大了岩石学研究的参与度，地球的上地幔含有一种不可磨灭的重惰性气体（Ar，Kr，Ar）元素丰度模式，与海水惊人地相似。由于这是太阳系中独特的成分，唯一可信的解释是，一种未被破坏的、类似海水的惰性气体特征在俯冲过程中幸存下来，通常认为排除了95%以上的挥发物。由于稀有气体在流体中的溶解度是地壳矿物的100至100，000倍，因此在变质流体的释放和运输过程中，即使是少量的相分离也会使俯冲岩石的稀有气体成分破裂。那么，在俯冲过程中，惰性气体是如何逃脱迁移和显著分馏的呢？而且，惰性气体能用来定量地追踪水的俯冲吗？该项目将通过整合稀有气体成分、矿物学结合的H2O含量以及对与俯冲有关的岩石的压力和温度的热力学估计来解决这些问题。拟议的研究将系统地检验惰性气体成分主要受俯冲过程中变质脱水程度控制的总体假设。在这个职业计划的教育部分的核心是开发和实施一系列的暑期学院，致力于提高岩石学研究的多样性。该计划将导致一批本科生的岩石学培训，其中许多人将来自少数民族服务机构。岩石学和地球化学数据集收集作为拟议的研究计划的一部分，将用于培养兴趣，并增加本科生的理解，从不同的机构和背景，在变质岩石学。这个奖项反映了NSF的法定使命，并已被认为是值得的支持，通过评估使用基金会的智力价值和更广泛的影响审查标准。