X-ray and Spectroscopic Studies of Subduction-Related Phases: Probing the Mid-Point of Volatile Recycling in the Earth

我们的水圈和大气中的主要物质，如水和二氧化碳，如何通过板块构造以固体矿物相的形式循环进入地球深处，然后最终在高压和高温下以流体相的形式释放出来，对于俯冲相关的火山活动（如环太平洋“火环”）是如何产生的，以及深部地震（深度大于200公里）的发生是至关重要的。在这个项目中，研究人员计划在高压和高温条件下检查相关的含水和含碳矿物，在这些矿物释放水和二氧化碳的条件下，确定：(1)它们的性质决定何时在深度释放水或二氧化碳；(2)水或二氧化碳是逐渐释放还是突然释放。这些结果将限制通过水引起的融化最终形成环太平洋火山活动的水是如何在地球深处释放的，并有助于模拟岩浆在深处的产生；并将探索二氧化碳是如何在深处释放的，以及它可能被运送到地表的形式。因此，这些结果对于大陆边缘的火山活动的产生，以及与俯冲相关的地震（可能是由流体润滑的）是如何产生的，具有根本的相关性。在进行这些实验时，该小组将率先开发一种新设备，该设备将供整个科学界使用，该设备旨在在劳伦斯伯克利国家实验室的先进光源中对材料进行高压/高温表征。该小组广泛地邀请本科生参与其研究工作，而这项资助支持的研究生中包括一名退伍军人。调查结果也被纳入PI所在机构的本科课程。研究小组计划：(1)利用高精度单晶x射线衍射，研究同时在高压和高温下进入地幔的挥发物的重要载体的性质；(2)利用红外光谱和拉曼光谱对高压下碳酸盐岩成因特征进行表征。与第一个目标相结合，这种支持将促进建立一个新的、社区可访问的、高压/高温同步加速器的单晶x射线衍射设施。进出地球内部的水和二氧化碳的循环是影响固体地球特性（通过它们对融化和流变的影响）和地球表面（通过水圈的体积和地球大气层的组成）的关键过程。该团队建议在俯冲条件下探索含挥发物相的性质，以深入了解：(1)地幔中含挥发物相的多态性（或者，什么是深度脱气）；(2)在高压和高温下含挥发物相的结构（研究为什么这些相含有挥发物）；(3)已知的将水带到深处的相（尤其是lawsonite和phenphentic micas）在接近（希望超过）脱水条件时的表现。它们还将为在地幔条件下与碳酸盐离子结合相关的丰富相多态性提供新的约束：这里的重点将放在富碱碳酸盐上，这些碳酸盐最近被证明与深部碳酸盐熔融有关，并且在高压条件下基本上没有受到质疑。该团队将利用该项目部署两名研究生来协助，工作，摇样机和调试一个新的，世界级的高压单晶x射线衍射装置，该装置将于明年在劳伦斯伯克利国家实验室（LBNL）的先进光源（ALS）建立并投入使用。该设施将通过ALS的一般用户计划提案过程向整个社区开放（该设施也将成为压缩联盟在ALS的批准计划的一部分，因此将为获得时间的用户提供帮助）。除了部署新的社区基础设施外，PI还将：(1)为不同群体的研究生（目前有一名退伍军人，一名归来的女性）和本科生的教育做出贡献；(2)继续为对地球自然史感兴趣的人出版/贡献具有广泛兴趣的文献（并酌情通过新闻稿进行宣传）；(3)将新成果纳入UCSC本科教学（通常每年约90个地球科学专业）。

How the major materials of our hydrosphere and atmosphere, such as water and carbon dioxide, are cycled into the deep Earth within solid mineral phases via plate tectonics, and then ultimately released as fluid phases at high pressures and temperatures, is of key importance for how subduction-associated volcanism (like the circum-Pacific "Ring of Fire") is produced, and also possibly for the occurrence of deep earthquakes (at depths greater than ~200 km). In this project, the investigators plan to examine water- and carbon-containing minerals of relevance under the high-pressure and high temperature conditions under which they release water and carbon dioxide to determine: (1) their properties that govern when water or carbon dioxide are released at depth; and (2) whether water or carbon dioxide are released gradually or abruptly. These results will constrain how the water that ultimately generates circum-Pacific volcanism via water-induced melting is released at depth in the planet, and help in the modeling of magma production at depth; and will explore how carbon dioxide is released at depth and the form in which it might be transported to the surface. Thus, these results have fundamental relevance for the production of volcanism at continental margins, and for how deep subduction-related earthquakes (which are likely greased by fluids) are generated. In conducting these experiments, the group will spearhead the development of a new facility, which will be available to the scientific community as a whole, which is designed to conduct high-pressure/high-temperature characterizations of materials at the Advanced Light Source at Lawrence Berkeley National Labs. The group extensively engages undergraduates in its research effort, and the graduate students supported by this grant include a military veteran. The results are also incorporated into undergraduate curricula at the PI's institution.The investigator team plans to: (1) examine the properties of important carriers of volatiles into Earth's mantle at simultaneous high pressures and high temperatures using high precision single-crystal x-ray diffraction; and (2) characterize the properties of carbonates of relevance to carbonatite petrogenesis at high pressures using infrared and Raman spectroscopy. In tandem with the first objective, the establishment of a new, community-accessible, high-pressure/high-temperature synchrotron-based single crystal x-ray diffraction facility will be facilitated by this support. The cycling of water and carbon dioxide into and out of Earth's interior are pivotal processes that impact both the properties of the solid Earth (through their effects on melting and rheology) and Earth's surface (through the volume of the hydrosphere and the composition of Earth's atmosphere). The team proposes to probe the properties of volatile-bearing phases under subduction conditions to gain insights into: (1) the polymorphism of volatile-bearing phases in Earth's mantle (or, what is degassing at depth); (2) the structures of volatile-bearing phases at high-pressures and temperatures (to examine why these phases hold volatiles); and (3) how phases that are known to carry water to depth (and particularly lawsonite and phengitic micas) behave as they approach (and hopefully exceed) their dehydration conditions. They also will provide new constraints on the rich polymorphism of phases associated with the binding of the carbonate ion under mantle conditions: the focus here will be on alkali-rich carbonates, which have recently been demonstrated to be associated with deep carbonatite melting, and which have largely been uninterrogated at high pressure conditions. The team will utilize this project to deploy two graduate students to assist, work through, shake down and debug a new, world-class high-pressure single-crystal x-ray diffraction set-up that will be set-up and commissioned over the next year at the Advanced Light Source (ALS) at Lawrence Berkeley National Labs (LBNL). This facility will be available to the community as a whole through the General User Program proposal process of the ALS (the facility will also be part of the COMPRES-Consortium's Approved Program at the ALS, and thus will have assistance for users who are awarded time). In addition to this deployment of new community infrastructure, the PI will: (1) contribute to the education of a diverse group of graduate students (currently, one military veteran, one returning female) and undergraduates; (2) continue to publish/contribute to the literature on topics of broad interest for those interested in the natural history of the planet (and promote these as appropriate with press releases); and (3) incorporate new results into UCSC undergraduate teaching (typically, to ~90 earth sciences majors per year).