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.

俯冲带是在构成地球刚性外壳的岩石圈板块被回收回地幔的地方形成的。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的地幔中。这会引起地幔熔化，并以爆炸性的地表火山活动的形式表现出来，例如太平洋盆地周围的火山活动（所谓的“火环”）。俯冲带相关的火山活动与经济矿藏的形成密切相关。不幸的是，从下降板块到上覆地幔的流体运动性质无法直接观察到。该项目将测试侵入浅层大陆地壳和脱水下伏岩石的大型火成岩体是否可以作为俯冲带热液系统深处过程操作的代理。这项研究将集中于蒙大拿州已有 27 亿年历史的斯蒂尔沃特综合体的入侵，该综合体后来因侵蚀而暴露出来。具体来说，计划研究流体从下伏岩石中释放并移动到上覆火成岩中的机制（裂缝、矿脉等）以及在此过程中这些流体被改变的程度。这项研究对于研究俯冲带发生的爆发性火山活动以及了解俯冲带环境和独特的岩浆侵入中的矿床所涉及的流体的最终来源有更广泛的应用，而独特的岩浆侵入是关键材料的主要来源。我们的现代工业。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，这项工作需要对斯蒂尔沃特杂岩体下部及其 2-3 公里厚的变质光环的热液特征（高温矿脉和伟晶体）进行测绘和表征。这将包括比较斯蒂尔沃特杂岩中脉伟晶体的稳定（特别是碳）和放射性（Nd、Sr和Pb）同位素组成与周围的主岩，以测试乡村流体参与其形成的程度。这些热液特征的组成将与斯蒂尔沃特杂岩直至中带状系列的块体岩石主量和微量元素组成进行比较，目前尚无对该杂岩的全面覆盖。这些现场数据可用于约束俯冲带和层状侵入环境中流体通道化的理论模型。它还可以为理解三相晶体-液体-气体糊状体中从岩浆到流体运移的转变提供见解，并对矿床形成模型产生影响。该奖项反映了 NSF 的法定使命，并被认为值得通过以下方式获得支持：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。