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Layered Intrusion-Footwall Hydrothermal Interactions - An Analog For Subduction Zone Hydrothermal Sytems

层状侵入-下盘热液相互作用 - 俯冲带热液系统的模拟

基本信息

批准号：
1647727
负责人：
A. Boudreau
金额：
$ 25.04万
依托单位：
Duke University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2018
资助国家：
美国
起止时间：
2018-06-01 至 2022-09-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1647727&HistoricalAwards=false
关键词：
Layered Intrusion Footwall Hydrothermal Interactions

项目摘要

Subduction zones are formed where lithospheric plates that make up the rigid, outer shell of the Earth are recycled back into the Earth's mantle. When that happens, the rigid plate is heated and releases water and other volatiles into the overlying mantle. This induces melting in the mantle and expresses itself in explosive surface volcanism, such as those around the Pacific Ocean basin (the so-called 'Ring of Fire'). Volcanism associated with subduction zones is closely linked to the formation of economic mineral deposits. Unfortunately, the nature of fluid movement from the descending slab into the overlying mantle cannot be directly observed. This project will test if large igneous bodies that intruded into the shallow continental crust and dehydrated underlying rocks can serve as proxies to processes operation at depth in subduction zone hydrothermal systems. The study will be centered on the intrusion of the 2.7 billion year old Stillwater Complex in Montana, and which has since been exposed by erosion. Specifically, it is planned to investigate mechanisms (fractures, veins, etc.) by which fluids liberated from the underlying rocks and moved into the overlying igneous rocks and the degree that these were modified during this process. The study has broader applications to the study of the explosive volcanism that occurs at subduction zones as well as understanding the ultimate source of fluids involved in ore deposits in both the subduction zone environment and in unique magmatic intrusions that are the main sources of critical materials for our modern industry. Copper, chromium and the platinum-group elements are examples of critical resources with great importance for the national economy. The funding also will help support advanced training for a graduate student and senior thesis projects for undergraduate students. More specifically, the work entails mapping and characterization of hydrothermal features (high temperature veins and pegmatoidal bodies) of the lower part of the Stillwater Complex and its 2-3 km thick metamorphic aureole. This will include comparing the stable (particularly carbon) and radiogenic (Nd, Sr, and Pb) isotopic composition of veins pegmatoidal bodies in the Stillwater Complex with the surrounding host rock to test the degree country fluids were involved in their formation. The composition of these hydrothermal features will be compared with bulk rock major and trace element composition of the Stillwater Complex up to the Middle Banded series, for which there currently is no comprehensive coverage of the complex. These field data can be used to constrain theoretic models of fluid channelization in both subduction zone and layered intrusion settings. It can also lead to insights toward understanding the transition from magmatic to country fluid migration in three-phase crystal-liquid-gas mushes, and has consequences for ore deposit formation 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.

俯冲带形成于构成地球坚硬外壳的岩石圈板块再循环回到地幔的地方。当这种情况发生时，刚性板块被加热并将水和其他挥发物释放到上覆地幔中。这导致地幔熔化，并表现为爆炸性的表面火山活动，例如太平洋盆地周围的火山活动（所谓的“火环”）。与俯冲带有关的火山作用与经济矿床的形成密切相关。不幸的是，流体从下降板块进入上覆地幔的运动性质无法直接观察到。该项目将测试侵入浅大陆地壳的大型火成岩体和脱水的下层岩石是否可以作为俯冲带热液系统深度作业过程的替代物。该研究将集中在蒙大拿州27亿年历史的静水复合体的入侵，该复合体已被侵蚀暴露。具体而言，计划调查机制（骨折、静脉等）。流体从下伏岩石中释放并进入上覆火成岩的方式，以及在此过程中这些岩石被改变的程度。该研究在研究俯冲带发生的爆炸性火山作用以及了解俯冲带环境和独特岩浆侵入体中矿床所涉及的流体的最终来源方面具有更广泛的应用，这些侵入体是关键物质的主要来源。我们现代工业的材料。铜、铬和铂族元素是对国民经济具有重要意义的关键资源。这笔资金还将帮助支持研究生的高级培训和本科生的高级论文项目。更具体地说，这项工作需要对静水杂岩下部的热液特征（高温脉和伟晶岩体）及其2-3公里厚的变质晕进行测绘和定性。这将包括比较稳定的（特别是碳）和放射性（Nd，Sr和Pb）同位素组成的静脉伟晶岩体在静水复杂与周围的寄主岩石，以测试的程度国家流体参与其形成。这些热液特征的组成将与静水杂岩直至中间带状系列的大块岩石主要和微量元素组成进行比较，目前还没有对该杂岩的全面报道。这些数据可以用来约束流体通道化的理论模型在俯冲带和层状侵入设置。它也可以导致对理解从岩浆到国家流体迁移在三相晶体-液体-气体糊状物的转变的见解，并对矿石存款形成模型产生影响。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智力价值和更广泛的影响审查标准进行评估的支持。