Melting Processes and Crust-Mantle Interaction in the Cascade Arc: Constraints from U-Series, Nd, Os, Pb and Sr Isotopic Data

叶栅弧中的熔化过程和壳幔相互作用：来自 U 系列、Nd、Os、Pb 和 Sr 同位素数据的约束

• 批准号: 0948703
• 负责人: Yemane Asmerom
• 金额: $ 29.24万
• 依托单位: University of New Mexico
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-15 至 2013-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0948703&HistoricalAwards=false
• 关键词: Melting; Processes; Crust; Mantle; Interaction

The subduction zone system on Earth is where net material transfer from the mantle to the continental crust occurs, and where material that is created at spreading ridges is returned to the mantle. Unlike volcanism in mid-ocean ridges, where melting components are limited and melting mechanism are considerably simpler, volcanism in arcs is considerably more complex: components of melt are numerous, such as the down going slab, the mantle wedge, the overlying mantle and continental lithospheres, fluids and sediments. As a result, arc magmas exhibit rich diversity in elemental and isotopic composition over short distances. It is generally agreed that fluid addition plays an important role in melting in subduction zones, most likely by hydrating the mantle wedge and lowering the solidus temperature. The timing of fluid addition and the extent of fluid involvement in generation of magmas in certain arcs, such as the Cascade subduction zone, are not clear. The Cascade arc represents both a slow converging and warm end-member of the global arc system. It is also one of the best characterized arcs, given almost century long geophysical and geologic studies. A uranium-series based study in this arc is ideally suited to answer a number of the outstanding questions. These include, 1) the relative importance of flux melting and dynamic melting in arcs in general and the Cascades in particular, 2) the explanation for the paradox of the estimated high pre-eruptive water content (up to 8% H2O) inferred for some Cascade lavas and yet the lack of enrichment in key fluid indicating elements and isotopic ratios, 3) and the amount of crust component in Cascade lavas. The proposed study will utilize 230Th-238U, 226Ra-230Th, 231Pa-235U, Sr, Nd, Pb and Os isotopic data on young lavas and mineral separates to address the above and related questions.Although this project's aim is answering basic scientific questions, it will support the human development and infrastructural building efforts at the University of New Mexico. The project will serve as a venue for training two graduate students in analytically-based geochemistry and petrology. The lab is used not only by the PIs group but also by a variety of other groups, including students from small undergraduate colleges, such as Cornell College, Iowa, and University of Puget Sound, Washington. The University of New Mexico is a minority serving institution and the current proposal is coupled to an existing Sloan Foundation grant to the PI to support minority PhD students. The study area is a National area of concern for volcanic hazards, and results from this project may contribute towards understanding of volcanic eruption cycles.

地球上的俯冲带系统是发生从地幔到大陆地壳的净物质转移的地方，也是在扩张脊处产生的物质返回到地幔的地方。 与大洋中脊的火山活动不同，其中熔化成分有限且熔化机制相当简单，弧中的火山活动要复杂得多：熔化成分众多，如下降板片、地幔楔、上覆地幔和大陆地幔。岩石圈、流体和沉积物。 因此，弧岩浆在短距离内表现出丰富的元素和同位素组成多样性。人们普遍认为，流体的添加在俯冲带的熔融过程中发挥着重要作用，最有可能是通过水合地幔楔并降低固相线温度。 在某些弧段（例如喀斯喀特俯冲带）中，流体添加的时间和流体参与岩浆生成的程度尚不清楚。 级联弧代表了全局弧系统的缓慢会聚和温暖的端部成员。鉴于近一个世纪的地球物理和地质研究，它也是特征最好的弧之一。 该领域基于铀系的研究非常适合回答许多悬而未决的问题。 其中包括，1) 一般而言，电弧中熔剂熔化和动态熔化的相对重要性，特别是喀斯喀特，2) 对某些情况下推断的估计高喷发前水含量（高达 8% H2O）的悖论的解释梯级熔岩，但关键流体指示元素和同位素比缺乏富集，3) 以及梯级熔岩中地壳成分的量。 拟议的研究将利用年轻熔岩和矿物分离物的 230Th-238U、226Ra-230Th、231Pa-235U、Sr、Nd、Pb 和 Os 同位素数据来解决上述及相关问题。虽然该项目的目的是回答基本科学问题，它将支持新墨西哥大学的人类发展和基础设施建设工作。 该项目将作为培训两名基于分析的地球化学和岩石学研究生的场所。 该实验室不仅供 PI 小组使用，还供其他各种小组使用，包括来自爱荷华州康奈尔学院和华盛顿州普吉特海湾大学等小型本科院校的学生。 新墨西哥大学是一所少数族裔服务机构，当前的提案与斯隆基金会向 PI 提供的现有拨款相结合，以支持少数族裔博士生。 该研究区域是国家关注的火山灾害区域，该项目的结果可能有助于了解火山喷发周期。