Quantifying Geochemical Exchange at the Slab-Wedge Interface with Experiments and Natural Samples

建议1447342用实验和自然样品量化板岩-楔形界面的地球化学交换PI：C.Till这个项目的目标是更好地了解当一个构造板块下沉到另一个板块之下时所产生的化学反应，将水和其他化学成分带入地球内部。该项目包括与日本同事的合作，并得到了国际科学和工程组织的部分支持。这种类型的板块俯冲产生了像火环那样的火山弧，以及每年地球上一些最大的地震。了解俯冲导致的化学反应对于了解为什么我们的星球有不同于太阳系其他行星的地壳类型，以及火山弧发出的气体和岩浆如何影响地球大气的组成，至关重要。尽管我们很早就知道俯冲作用促成了这些行星范围的过程，但关于板块衍生的元素与地球地幔发生反应的具体化学反应，仍然存在许多问题。这种知识的缺乏在很大程度上是由于自上而下研究俯冲系统的局限性，部分可以通过研究来自地幔的稀有样品结合这里提出的高压实验来解决。第二部分：这个项目解决了关于俯冲板块-地幔界面的三个具体问题：1)含水矿物，特别是绿泥石，是否形成在地幔楔形的底部，并在高压实验和硼同位素分馏研究所假设的弧状岩浆的形成中发挥关键作用？2)俯冲沉积物熔体的成分是否与实验预测相似，并随后与地幔反应，产生地球化学模型预测的安山岩浆？3)俯冲板块熔体是否如弧岩浆和熔体包裹体的地球化学研究所争论的那样氧化地幔？为了回答这些问题，我们提出了对日本东-赤石超镁铁质杂岩中稀有橄榄岩和榴辉岩矿物的主元素和微量元素、Fe3+/Fet和B同位素组成的原位分析，它们代表了从地幔楔体底部剥离出来的残留岩和圈闭熔体。整个岩石和矿物化学数据还将用于限制沉积物熔体-地幔楔形反应高压实验的起始成分，以补充现场化学和同位素分析。

Abstract for Proposal 1447342 Quantifying Geochemical Exchange at the Slab-Wedge Interface with Experiments and Natural SamplesPI: C. TillThe goal of this project is to better understand the chemical reactions that result when one tectonic plate sinks below another, bringing water and other chemical constituents into the Earth's interior. The project includes collaboration with Japanese colleagues and is partly supported by International Science and Engineering. This type of plate-subduction produces volcanic arcs like those in the Ring of Fire, as well as some of the largest earthquakes on Earth every year. Understanding the chemical reactions that occur as a result of subduction is ultimately important to understand why our planet has a different type of crust than the other planets in our solar system, and how the gases and magmas emitted from volcanic arcs affect the composition of the Earth's atmosphere. Although we have long understood that subduction contributes to these planet-wide processes, many questions remain about the specific chemical reactions in which the plate-derived elements react with the Earth's mantle. This lack of knowledge is largely due to the limitations of studying subduction systems from the top down and can, in part, be resolved by studying rare samples from the mantle in conjunction with high-pressure experiments as proposed here.Part 2:This project addresses three specific questions about geochemical exchange at the subducted plate- mantle interface: 1) Do hydrous minerals, in particular chlorite, form at the base of the mantle wedge and play a key role in the formation of arc magmas as hypothesized by high-pressure experiments and studies of boron isotope fractionation?, 2) Does the composition of subducted sediment melt resemble experimental predictions and subsequently react with the mantle to produce andesitic arc magmas as predicted by geochemical models?, and 3) Do subducted plate fluxes oxidize the mantle as debated by geochemical studies of arc magmas and melt inclusions? To answer these questions we propose in-situ analyses of the major and trace element, Fe3+/FeT, and boron isotopic composition of rare peridotite and eclogite minerals from the Higashi-akaishi ultramafic complex, Japan, which represent restites and trapped melts exhumed from the base of the mantle wedge. The whole rock and mineral chemistry data will also be used to constrain starting compositions for high-pressure experiments on sediment melt-mantle wedge reactions in a complimentary effort to the in-situ chemical and isotopic analyses.