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

俯冲带形成于组成坚硬的地球外壳的岩石圈板块被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面的地幔中。这导致地幔熔化，并表现为表面爆发的火山作用，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藏的形成密切相关。不幸的是，无法直接观察到流体从下降板进入上地幔的性质。该项目将测试侵入浅层大陆地壳和脱水的下伏岩石的大型火成体是否可以作为俯冲带热液系统中深部作业的替代品。这项研究将集中在蒙大拿州有27亿年历史的斯蒂尔沃特建筑群的入侵，自那以来，该建筑群已被侵蚀暴露。具体地说，计划研究机制(骨折、静脉等)。流体从下伏岩石释放并进入上覆火成岩的程度，以及这些岩石在这一过程中被修改的程度。这项研究在研究俯冲带发生的火山爆发作用以及了解俯冲带环境和独特岩浆侵入体中的矿床中所涉及的流体的最终来源方面有着更广泛的应用，这些都是我们现代工业的关键材料的主要来源。铜、铬和铂族元素是对国民经济具有重要意义的关键资源。这笔资金还将用于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，这项工作需要绘制和描述斯蒂尔沃特杂岩下部及其2-3公里厚的变质光环的热液特征(高温矿脉和伟晶状矿体)。这将包括比较静水杂岩中脉状矿体的稳定(特别是碳)和放射成因(Nd、Sr和Pb)同位素组成与周围围岩，以测试国家流体参与其形成的程度。这些热液特征的组成将与Stillwater杂岩的主体岩石和微量元素组成进行比较，直到中条带状系列，目前还没有关于该杂岩的全面报道。这些野外资料可以用来约束俯冲带和层状侵入体环境中流体通道作用的理论模型。它还有助于深入了解三相晶体-液体-气体熔体中从岩浆向国家流体迁移的转变，并对矿床形成模型产生影响。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.