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: 1264560
• 负责人: Adam Simon
• 金额: $ 37.94万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 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 2016-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1264560&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.

智力优点：在变质脱水下的海洋岩石圈和上覆的沉积物，因为这些材料被俯冲（即压力和温度的增加）。假设这一过程是为了解释弧岩层中与众不同的地球化学特征，而不是来自中山山脊（Morb）和海洋岛（OIB）的岩浆。基础过程涉及在液体岩石反应过程中溶解的流体在选择性分数元件中的能力。提出了相对于高田间强度元素（HFSE：NB，NB，ZR，TA，HF，TI），并相对于在轻度（Lree）中，相对于中间和重型（Med-Mudlid-eveere）（Med-Ree）（Med-Ree，Meree，Meree，Hree，Hree，Hree，Hree，Hree，Hree，Hree）。目前，量化此类过程所需的数据主要用于纯或稀释水溶液，并覆盖了P-T空间中相对较小的区域，在该程序中，程序变质脱水发生在前臂和Subarc环境中。提出了实验研究，以显着扩大我们对REE和HFSE在水性流体中的行为的了解，这是俯冲带条件下的流体化学，压力和温度的函数。例如，将在金红石和流体之间，洛杉矶和流体之间的LA和CE进行分配，以及异种和流体之间的y，y对于一系列流体散装组成，包括H2O-NACL和H2O-NAF系统，用于确保液体含有足够的液体相对于本质上预期的si。因此，这项工作将允许评估溶解的Cl，F和Si对逼真的水性液体中痕量元件溶解度的影响。将使用两种完整的实验技术：1）在1-3 GPA和300-600°C下的水热钻石砧细胞（HDAC），其中NB，LA，CE和Y浓度将通过使用Synchrotron X射线荧光（SXRF）进行原位测量； 2）在1和1.8 GPA和700-900°C下的活塞缸设备，其中将通过使用质量损坏技术与回收晶体的LA-ICP-MS分析一起测量流体中的痕量元素浓度，以评估固体阶段溶解的一致性的性质。通过测量异种溶解度，在HCl-H2O流体中测量异种溶解度，从而证明了实验技术的成功开发和校准（并在本提案中进行了描述）。新的结果将显着增加有限的矿物流体分配数据库，而不是感兴趣的压力温度制度，并使地质学家能够更准确地对俯冲带环境中流体至上的变质和岩浆作用建模。更广泛的影响：该项目涉及将三名UNLV教师之间的合作，他们将其专业知识与一名精神一名女博士生伊丽莎白·塔尼斯（Elizabeth Tanis）女士以及每年至少有两名UNLV本科生。博士生已经在研究该项目，并在两次AGU会议上介绍了数据，以及一项提交的手稿，该手稿被接受。所有学生都将接受基于尖端同步加速器的实验技术，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，重要的是，将通过与UNLV，纽芬兰大学纪念大学和纽芬兰大学的纪念大学和高级光子科学家的纪念化学家合作，通过与科学家的科学家合作建立研究关系。 PI定期参加社区外展活动，向K-12学生展示讲座和动手地质演示。西蒙（Simon）和伯恩利（Burnley）定期访问K-12课程，西蒙（Simon）是UNLV-Clark县学区“夏季学院”的地球科学成员，该学院每年夏天将60名K-5教师参加UNLV，从事强化科学课程教育以及Clark Magnate High School Science Olympiade Olympiad Team，2011年至2012年的Clark Magnate High School Science Team。结果将直接纳入PIS教授的课程中，结果将在适当的科学会议上介绍，并在同行评审的期刊上发布。