Experimental Investigations of the Role of H2O in Subduction Zone Processes

技术说明：将开展三个项目。 1)H2O存在下地幔熔融的实验研究将确定关键矿物的化学组成和熔体的组成。 这些结果将被用来了解的过程，从俯冲大洋岩石圈到地幔楔橄榄岩的水转移。2)将对1至2 GPa（地球深度30至60公里）的浅层地幔熔融进行系统调查。 这些实验将使用地幔模拟成分和H2O量的受控变化。 他们的目的是提供限制的磁通熔化和反应性的地幔楔中的多孔流动的定量模型的发展。3)弧形安山岩到流纹岩的地壳水平分离结晶实验研究。 这些实验将在100至300 MPa的压力下进行，在H2O饱和条件下的氧逸度范围内，并将校准斜方辉石熔体温度计和湿度计。 该温湿度计可广泛应用于安山岩-流纹岩岩浆中。 4)安山岩和英安岩熔岩的平行地球化学和岩石学研究。Shasta和纽贝里火山的喀斯喀特山脉，美国提供地壳分异过程的定量信息。 在所有的实验研究中，我们将开发定量的，基于化学的分析工具，允许估计的熔化/结晶过程中H2O参与。通过俯冲带环境的H2O通量的影响是了解地球的壳幔系统在过去的45亿年的化学演化的根本重要性。这一信息的影响H2O的熔融和结晶过程将使我们能够开发更好的模型，耦合地幔流与俯冲。 最终，这项研究与地球的起源有关吗？海洋和大气的演变。更广泛的意义和重要性：这项工作将推进我们对俯冲带环境中岩浆形成过程的理解。 H2O是形成这些从火山喷发的岩浆的关键成分（如Mt.或者在深层冷却结晶形成地壳。 通过了解水对岩浆生成过程中的温度和化学反应的影响，我们将更好地了解化学元素在这些岩浆中的位置和方式，以及在地球内部循环的H2O的位置和数量。 这是地球科学中一个基本的重要问题，对许多实际问题都有影响。 两个直接的公众利益是：1）矿床的形成，集中了具有经济重要性的元素（如铜，锌，铅），它们可以被提取，2）H2O是产生危险的火山爆发的活性成分，这是俯冲火山的标志：知道H2O的数量可以被纳入是理解这些火山爆发如何工作的基础。

Technical description:Three projects will be carried out. 1) Experimental studies mantle melting in the presence of H2O will determine the chemical composition of key minerals and the composition of the melt. These results will be used to understand the processes that transfer H2O from the subducted oceanic lithosphere into mantle wedge peridotite. 2) A systematic investigation of shallower mantle melting from 1 to 2 GPa (30 to km 60 depth in the Earth), will be carried out. These experiments will use mantle analog compositions and controlled variations in the amount of H2O. Their purpose is to provide constraints for the development of quantitative models of flux melting and reactive porous flow in the mantle wedge. 3) Experimental studies on crustal- level fractional crystallization of arc andesites to rhyolites. These experiments will be carried out at pressures of 100 to 300 MPa over a range of oxygen fugacities under H2O-saturated conditions and will calibrate an orthopyroxene-melt thermometer and hygrometer. This thermometer-hygrometer will be widely applicable to andesite-rhyolite magmas. 4) Parallel geochemical and petrologic investigations on andesite and dacite lavas from Mt. Shasta and Newberry volcano in the Cascades, USA to provide quantitative information on crustal differentiation processes. In all of the experimental studies we will develop quantitative, thermodynamically based analytical tools that allow estimation of melting/crystallization processes where H2O is involved. The effects of H2O flux through the subduction zone environment are of fundamental importance for understanding the chemical evolution of the Earth's crust-mantle system over the last 4.5 billion years. This information on the influence of H2O on melting and crystallization processes will allow us to develop better models that couple mantle flow with subduction. Ultimately, the research has relevance for the origin of the Earth?s oceans and the evolution of the atmosphere. Broader significance and importance:This work will advance our understanding of the processes that lead to the formation of magmas in subduction zone environments. H2O is a key ingredient in the formation of these magmas that erupt from volcanoes (like Mt. St. Helens) or cool and crystallize at depth to form the Earth's continental crust. By understanding water's influence on the temperature and chemical reactions of this magma generation process, we will gain a better understanding of where and how chemical elements are concentrated in these magma and where and how much H2O is recycled through the Earth's interior. This is a fundamentally important problem in Earth Science that has implications for a number of practical matters. Two of immediate public interest are: 1) the formation of ore deposits that concentrate elements of economic importance (e.g. Cu, Zn, Pb) where they can be extracted and 2) H2O is the active ingredient in producing the dangerous volcanic eruptions that are the signature of subduction volcanoes: knowing the amount of H2O that can be incorporated is fundamental fro understanding how these eruptions work.