Collaborative Research: Tracking Novel Metal Isotope Signatures during Subduction Metamorphism

合作研究：追踪俯冲变质作用过程中的新金属同位素特征

• 批准号: 1949655
• 负责人: Shelby Rader
• 金额: $ 6.2万
• 依托单位: Indiana University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-04-01 至 2024-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1949655&HistoricalAwards=false
• 关键词: Collaborative; Research; Tracking; Novel; Metal

Subduction is a key geologic process governing the Earth’s chemical evolution. Through this process, sediments bearing the chemical signatures of low-temperature interaction with the hydrosphere and atmosphere are delivered, along with ocean crust altered by interaction with seawater, to the Earth’s deep interior. With increasing depth and pressure, metamorphic changes to the subducting slab’s mineralogy lead to the release of fluids and, in some cases, melts, enriched in some elements over others. These materials may return to the Earth’s surface via the route of arc volcanism, leaving behind a chemically altered slab that continues to sink deeper into the mantle. The research broadly aims to better understand the chemical exchange that occurs between the slab and overlying mantle during subduction metamorphism using the molybdenum (Mo) and thallium (Tl) isotope tracer systems. Isotopes of Mo and Tl experience strong fractionation in the oceans, leading to distinct isotope signatures in sediments and altered ocean crust that are ultimately transferred to subduction zones. While recent research on the Mo and Tl isotope systems in volcanic arc rocks indicate that Tl isotopes match subduction zone inputs well, there is a large mismatch between the Mo isotope composition of most arcs and subduction zone inputs. The work will focus on the origins of the divergent behaviors of the Mo and Tl isotope systems and provide new understanding of the deep Earth cycling of these elements. The work uses two well-characterized suites of high pressure-low temperature (HPLT) metamorphic rocks as analogs for the chemical processes and mineralogical changes that occur in sedimentary rocks during subduction. The Schistes Lustres and related rocks from the western Alps exhibit a metamorphic gradient that ultimately reaches pressures approaching 3 GPa, but prior work has shown only limited mobile-element loss. The Catalina Schist from California represents warmer subduction metamorphic conditions and shows considerable mobile element loss. The bulk-rock Mo and Tl isotope compositions of the two sample suites will be determined in order to ascertain whether these isotope systems experience fractionation during HPLT metamorphism. In situ analysis via LA-ICP-MS will determine which minerals host these elements and how they are redistributed during progressive metamorphism. Isotope analysis of purified mineral splits will determine whether isotopic fractionation occurs between mineral phases.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.

俯冲是管理地球化学演化的关键地质过程。通过这一过程，带有与水圈和大气相互作用的化学特征的沉积物以及与海水与海水的相互作用改变的海皮与地球内部的深层内部。随着深度和压力的增加，俯冲板的变质变化导致液体释放，在某些情况下会融化，富含某些元素，而不是其他元素。这些材料可以通过弧火山的途径返回地球表面，留下化学变化的平板，该平板继续深入地幔。该研究广泛地旨在更好地了解使用钼（MO）和Thallium（TL）同位素示踪系统在俯冲变质过程中板和上覆盖层之间发生的化学交换。 MO和TL的同位素在海洋中经历了强烈的分馏，从而导致沉积物中不同的同位素特征，并改变了最终转移到俯冲带的海壳。尽管火山弧岩石中的MO和TL同位素系统的最新研究表明，TL同位素匹配俯冲带的输入很好，但大多数弧和俯冲带的MO同位素组成之间存在很大的不匹配。这项工作将集中于MO和TL同位素系统不同行为的起源，并提供对这些元素深层循环的新理解。这项工作使用了两个高压低温（HPLT）变质岩石的特征良好的套件，作为化学过程的类似物和俯冲过程中沉积岩石中发生的矿物学变化。来自西阿尔卑斯山的Schistes Lustres和相关岩石暴露了一种变质​​梯度，最终达到3 GPA的压力，但先前的工作仅显示出有限的移动元素损失。来自加利福尼亚州的Catalina片岩代表变暖的变质状况，并显示出相当大的移动元件损失。将确定两个样品套件的散装岩石MO和TL同位素组成，以确定在HPLT变质过程中这些同位素系统是否经历分馏。通过LA-ICP-MS进行原位分析将确定哪些矿物质托有这些元素，以及它们在进行性变质过程中如何重新分布。纯化的矿物拆分的同位素分析将确定同位素分级是否发生在矿物阶段之间。该奖项反映了NSF的法定任务，并使用基金会的知识分子优点和更广泛的影响来评估，被视为珍贵的支持。

项目成果

Forming Earth’s Continental Crust: A Nontraditional Stable Isotope Perspective

地球大陆地壳的形成：非传统稳定同位素视角

• DOI: 10.2138/gselements.17.6.413
• 发表时间: 2021
• 期刊: Elements
• 影响因子: 4.5
• 作者: Aarons, Sarah M.;Johnson, Aleisha C.;Rader, Shelby T.
• 通讯作者: Rader, Shelby T.

Thallium behavior during high-pressure metamorphism in the Western Alps, Europe

• DOI: 10.1016/j.chemgeo.2021.120349
• 发表时间: 2021-09
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: Shelby T. Rader;R. Gaschnig;S. Newby;G. Bebout;Michael J. Mirakian;J. Owens