Quantifying Rare Earth (REE) and High Field Strength (HFSE) Element Mobility in Fluids at Conditions Appropriate for Forearc to Subarc Cold and Hot Subduction Zones

在适合弧前至弧下冷俯冲带和热俯冲带的条件下量化流体中稀土 (REE) 和高场强 (HFSE) 元素的迁移率

• 批准号: 1220548
• 负责人: Adam Simon
• 金额: $ 37.94万
• 依托单位: University of Nevada Las Vegas
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-15 至 2012-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1220548&HistoricalAwards=false
• 关键词: Quantifying; Rare; Earth; REE; Field

Intellectual Merit: Ocean lithosphere and overlying sediments undergo metamorphic dehydration as these materials are subducted (i.e., increasing pressure and temperature). This process has been hypothesized to account for distinctive geochemical signatures in arc magmas as opposed to those from mid-ocean ridges (MORB) and ocean islands (OIB). The underlying process involves the ability of exsolved fluids to selectively fractionate elements during fluid-rock reactions. The fluid is proposed to enrich arc magmas in the large ion lithophile elements (LILE: K, Rb, Cs, Sr, Ba) relative to high field strength elements (HFSE: Nb, Zr, Ta, Hf, Ti), as well as enriching the magmas in light-REE (LREE) relative to the middle- and heavy-REE (MREE, HREE). At present, data needed to quantify such processes are mostly available for pure or dilute aqueous solutions and cover a relatively small area in the P-T space wherein prograde metamorphic dehydration occurs in the forearc and subarc environments. Experimental studies are proposed to expand significantly our knowledge of the behavior of the REE and HFSE in aqueous fluid as a function of fluid chemistry, pressure and temperature at subduction zone conditions. For example, the partitioning of Nb between rutile and fluid, La and Ce between monazite and fluid, and Y between xenotime and fluid will be determined for a range of fluid bulk compositions, including H2O-NaCl and H2O-NaF systems, with quartz used to ensure the fluid contains sufficient Si relative to that expected in nature. This work will thus allow assessment of the effects of dissolved Cl, F and Si on trace element solubilities in realistic aqueous fluids. Two complementary experimental techniques will be used: 1) a hydrothermal diamond anvil cell (HDAC) at 1 - 3 GPa and 300-600°C, wherein Nb, La, Ce and Y concentrations will be measured in situ by using synchrotron X-ray fluorescence (SXRF); and 2) a piston-cylinder apparatus at 1 and 1.8 GPa and 700-900°C, wherein trace element concentrations in fluid will be measured by using the mass-loss technique combined with LA-ICP-MS analysis of recovered crystals to assess the nature of congruent dissolution of the solid phases. Successful development and calibration of the experimental technique was demonstrated (and described in this proposal) by measuring xenotime solubility, hence Y abundance, in a HCl-H2O fluid to 5 GPa. New results will add significantly to the limited mineral-fluid partitioning data base over pressure-temperature regime of interest, and allow geologists to model more accurately the effects of fluid-present metamorphism and magmatism in the subduction zone environment. Broader Impacts: This project involves collaboration between three UNLV faculty members who combine their expertise to mentor one female PhD student, Ms. Elizabeth Tanis, and at least two UNLV undergraduate students per year. The PhD student is already working on this project and has presented data at two AGU meetings as well as one submitted manuscript that is accepted pending revision. All students will be trained in cutting-edge synchrotron-based experimental techniques, piston-cylinder mass loss experiments, analytical chemistry and interpretation of geochemical data sets, and, importantly, will develop research relationships with a diverse group of scientists through collaboration with faculty at UNLV, Memorial University of Newfoundland and beamline scientists at the Advanced Photon Source. The PIs participate regularly in community outreach, presenting lectures and hands-on geology demonstrations to K-12 students. Simon and Burnley regularly visit K-12 classes, and Simon is the Geoscience member of a UNLV-Clark County School District "summer institute" that brings 60 K-5 teachers to UNLV each summer for intensive science-curriculum education as well as the Geoscience content mentor for the Clark Magnate High School science Olympiad team in 2011-2012. Results will be incorporated directly into courses taught by the PIs, and results will presented at appropriate science meetings and published in peer-reviewed journals.

知识专长：海洋岩石圈和上覆沉积物在俯冲过程中经历变质脱水（即，增加压力和温度）。这一过程被认为是弧岩浆与大洋中脊（MORB）和洋岛（OIB）岩浆不同的地球化学特征。潜在的过程涉及出溶流体在流体-岩石反应期间选择性地压裂元素的能力。流体富集弧岩浆中的大离子亲石元素（LILE：K，Rb，Cs，Sr，Ba）相对于高场强元素（HFSE：Nb，Zr，Ta，Hf，Ti），以及富集轻稀土元素（LREE）相对于中，重稀土元素（MREE，HREE）。 目前，量化这些过程所需的数据大多是纯或稀水溶液，并涵盖了一个相对较小的面积在P-T空间，在弧前和弧下环境中发生的变质脱水。实验研究提出了显着扩大我们的知识的稀土元素和HFSE在水性流体中的流体化学，压力和温度在俯冲带条件下的函数的行为。例如，对于一系列流体本体组成，包括H2O-NaCl和H2O-NaF系统，将确定Nb在金红石和流体之间的分配、La和Ce在独居石和流体之间的分配以及Y在磷钇矿和流体之间的分配，其中石英用于确保流体相对于自然界中预期的含有足够的Si。因此，这项工作将允许评估的影响，溶解的氯，氟和硅对微量元素的溶解度在现实的水性流体。将使用两种互补的实验技术：1）在1 - 3GPa和300-600°C下的水热金刚石压砧单元（HDAC），其中将通过使用同步加速器X射线荧光（SXRF）原位测量Nb、La、Ce和Y的浓度;和2）活塞-气缸装置，在1和1.8GPa和700-900 ℃下，其中流体中的痕量元素浓度将通过使用质量损失技术结合LA-ICP-MS来测量。对回收的晶体进行MS分析，以评估固相的一致溶解的性质。实验技术的成功开发和校准通过测量磷钇矿在HCl-H2O流体中至5 GPa的溶解度（因此Y丰度）来证明（并在本提案中描述）。 新的结果将显着增加有限的矿物流体分区数据库的压力-温度制度的利益，并允许地质学家更准确地模拟流体存在的变质作用和岩浆作用在俯冲带环境的影响。更广泛的影响：该项目涉及三名UNLV教职员工之间的合作，他们联合收割机结合自己的专业知识，每年指导一名女博士生Elizabeth Tanis女士和至少两名UNLV本科生。博士生已经在这个项目上工作，并在两次AGU会议上提交了数据，以及一份提交的手稿，被接受等待修订。所有学生都将接受尖端的同步加速器实验技术，活塞缸质量损失实验，分析化学和地球化学数据集的解释的培训，重要的是，将通过与UNLV，纽芬兰纪念大学和先进光子源的光束线科学家合作，与不同的科学家群体建立研究关系。PI定期参加社区外展活动，为K-12学生提供讲座和动手地质演示。西蒙和伯恩利定期访问K-12类，西蒙是UNLV克拉克县学区“暑期研究所”的地球科学成员，每年夏天将60名K-5教师带到UNLV进行强化科学课程教育，以及2011-2012年克拉克马纳特高中科学奥林匹克队的地球科学内容导师。研究结果将直接纳入PI教授的课程，研究结果将在适当的科学会议上发表，并发表在同行评审的期刊上。

项目成果

HIMU geochemical signature originating from the transition zone

• DOI: 10.1016/j.epsl.2020.116323
• 发表时间: 2020-07-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Huang, Shichun;Tschauner, Oliver;Tischler, Jon
• 通讯作者: Tischler, Jon