CSEDI Collaborative Research: C-O-H Volatile Metasomatism in the Cratonic Mantle - Implications for Mid-Lithospheric Discontinuities

地球是太阳系中唯一一颗表面分为海洋和大陆的行星。因此，了解大陆的起源以及它们的一部分如何在数十亿年内保持稳定，是了解地球演化的核心。古老而稳定的大陆核心（地幔）下面是厚厚的地幔层（位于地壳下面的地球硅酸盐层），这些地幔根被认为有助于大陆的稳定。然而，大陆地幔是如何形成和演化的仍然存在争议。特别是，岩浆或流体与地幔相互作用的作用，无论是在大陆形成期间或之后，是不清楚的，虽然广泛的分层观察到的地幔中的地震成像可能是由岩浆和流体相关的过程。这项研究将限制的熔体/流体和地幔反应，是一致的地球物理观测在岩石圈中部深度的包围方案的形成和演化的dronons。研究结果-通过同行评审的出版物，会议演示和座谈会，教室讲座和活动传播-将影响广泛的地球科学子学科，包括岩石学地球化学，矿物物理学，地球动力学和地震学。该提案将支持高温实验岩石学、矿物物理学和地震学领域的女博士生，并支持几名本科生的研究活动，包括来自代表性不足群体的学生。除了他们自己的研究，所有的学生将参与讨论，并与所有3个PI一起撰写研究文章，学习如何将固体地球科学的三个不同但相关的子学科的概念和方法联合收割机结合起来。因此，该提案将直接促进几名学生在其职业生涯的不同阶段的教育经验和专业发展。拟议的研究还将支持矿物物理学领域的早期职业PI，并将帮助研究人员吸引K-12学生参与科学。大陆内部20 - 30亿年的稳定性是地球动力学和热演化的关键特征。因此，了解地幔的地球物理结构、岩石学和物质特性，以及产生它们的构造历史，是地球科学面临的重大挑战之一。陆下地幔的一个奇特特征是在60-150 km深处存在明显的地震剪切速度降低，通常称为中岩石圈不连续面（MLDs）。由于MLD在克拉通内的广泛存在，它们的起源可能与克拉通形成有关;然而，MLD和克拉通形成之间的因果关系尚未建立，MLD的起源仍然存在很大争议。一种假设是MLDs代表富含CO2-H2O挥发物的区域，这导致含水和/或碳酸盐矿物或部分熔体的稳定性。本计画将借由整合实验岩石学、矿物物理学及地震学的结果来验证此假说。通过实验室实验，该项目将限制在MLD深度的混合CO2-H2O挥发物熔融的地幔橄榄岩的相平衡，考虑到挥发物引入的代理可能会随着克拉通形成模型而变化。我们的目标将是确定部分熔体的含水和碳酸盐矿物相的稳定性，并获得矿物相的组成和比例作为深度，温度和熔体/流体的函数：橄榄岩的比例为每种情况下。在相平衡实验和捕虏体数据的指导下，利用共振超声光谱（罗斯）和第一性原理模拟确定了角闪石和云母的适当端元和中间固溶体的热弹性性质。利用实验中的矿物组合和新矿物物理学中更新的弹性数据，将预测地幔速度模型。这些将比较南部非洲克拉通（通过联合反演表面波，Sp和Ps数据）和北美的地幔模型，并用于计算合成Sp和Ps接收器函数堆栈，将比较全球MLD观测。拟议的研究将测试是否一个或几个方案的流体/熔体渗透到地幔，如果有的话，满足地球物理和岩石学特征的大陆地幔在岩石圈中部的深度。我们的研究还将产生具体的产品，如贫化地幔+CO2+H2O的固相线参数化;交代地幔矿物组合作为P-T，渗透流体/熔体成分和流体/熔体：岩石比的函数;用更新的热弹性数据计算MLD相关组合的地震速度的代码;和观测到的地幔不连续参数和地幔速度模型。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的学术价值和更广泛的影响审查标准。

Earth is the only planet in the Solar System whose surface is divided into oceans and continents. Hence understanding the origin of continents and how portions of them remain stable for billions of years is central to understanding the evolution of the Earth. The old, stable cores of continents (cratons) are underlain by thick layers of mantle (the silicate layer of the Earth that lies below the crust), and these mantle roots are thought to contribute to continental stability. Yet, it remains debated how the continental mantle formed and evolved. In particular, the roles of magma or fluid interaction with the mantle, either during or after the continent formation, are unclear, although widespread layering observed in the cratonic mantle by seismic imaging may have been created by magma and fluid related processes. This research will constrain the formation and evolution of cratons by bracketing scenarios of melt/fluid and mantle reactions that are consistent with geophysical observations at mid-lithospheric depths. The research findings - disseminated through peer-reviewed publications, conference presentations and colloquia, and class room lectures and activities - will impact a wide range of Earth science sub-disciplines including petrology-geochemistry, mineral physics, geodynamics, and seismology. The proposal will support female PhD students in high P-T experimental petrology, mineral physics, and seismology, and support the research activities of several undergraduate students, including students from underrepresented groups. In addition to their own research, all the students will participate in discussions and write research articles together with all 3 PIs, learning how to combine concepts and methods from three different yet related sub-disciplines of solid Earth science. The proposal will thus directly further the educational experience and professional development of several students at various stages of their careers. The proposed research will also support an early career PI in the field of mineral physics and will aid the investigators in engaging K-12 students in science.The stability of the continental interiors for 2-3 billion years is a key feature of the Earth's dynamical and thermal evolution. Understanding the geophysical structure, petrology, and material properties of cratonic mantles and the tectonic history that produced them is therefore one of the grand challenges of Earth science. A curious feature of subcontinental mantles is the presence of distinct reductions in seismic shear velocity at depths of 60-150 km, often called mid-lithospheric discontinuities (MLDs). Given the widespread occurrence of MLDs within cratons, their origins may be linked to craton formation; however, the causal link between MLD and craton formation is yet to be established, and MLD origins remain highly debated. One hypothesis is that MLDs represent zones enriched in CO2-H2O volatiles, which led to stability of hydrous and/or carbonate minerals or partial melts. This project will test this hypothesis by integrating results from experimental petrology, mineral physics, and seismology. Through laboratory experiments, this project will constrain the phase equilibria of cratonic mantle peridotites fluxed by mixed CO2-H2O volatiles at MLD depths, taking into consideration how the agent of volatile introduction may vary with craton formation models. The goal will be to determine the stability of hydrous and carbonate mineral phases over partial melts and obtain the compositions and proportions of mineral phases as a function of depth, temperature, and melt/fluid:peridotite ratio for each of the cases. Guided by the phase equilibria experiments and compiled xenolith data, thermoelastic properties of the appropriate end members and intermediate solid solutions of amphibole and mica will be determined using Resonant Ultrasound Spectroscopy (RUS) and first principles simulation. Using the mineral assemblages from experiments and updated elasticity data from new mineral physics, mantle velocity models will be predicted. These will be compared to mantle models for southern African craton (to be obtained by joint inversion of surface wave, Sp and Ps data) and North America, and used to calculate synthetic Sp and Ps receiver function stacks that will be compared to MLD observations globally. The proposed research will test whether one or several scenarios of fluid/melt infiltration into cratons, if any, satisfy the geophysical and petrologic characters of continental mantles at mid-lithospheric depths. Our research will also lead to specific products such as solidus parameterizations of depleted mantle+CO2+H2O; metasomatized mantle mineral assemblages as a function of P-T, infiltrated fluid/melt composition and fluid/melt:rock ratio; codes for computing seismic velocities for MLD-related assemblages with updated thermoelastic data; and observed mantle discontinuity parameters and mantle velocity models.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.