Experimental Investigations on the Role of H2O in Magmatic Processes

智力优势：提出了建立水对上地幔熔融温度和压力以及地壳分异结晶影响的定量模型的实验。水在地球内部的循环对于理解地球在地质时期的化学演化具有根本的重要性。H2O在火成岩过程中的重要性早已为人所知，但对H2O影响的实验校准却很少。这些数据对于开发定量工具来估计岩浆中H2O丰度和了解H2O对岩浆过程的影响是必要的。为了取得进展，需要对广泛的实验项目进行新的测量。提出了三个项目。1)系统研究了H2O对天然玄武岩熔体液相的影响。这些实验将确定不同量的水对液相温度的影响。这些实验将构成熔点降低模型的基础，并有助于解决关于少量水对熔点影响的相当大的不确定性。2)水、压力和地幔成分对石榴石橄榄岩熔融作用的研究。这些实验将定量估计水和地幔体组成（主要是碱元素Na2O和K2O）对俯冲带和次大陆地幔环境中岩浆组成和温度的作用。3)水和压力对地壳玄武岩熔体分晶作用的实验研究。在弧岩浆系统中，分异弧岩浆的组成特征及其矿物组合为火山爆发前的水含量、温度和深度分异史提供了依据。玄武岩和安山岩岩浆的实验研究将在水饱和条件下，在300至800兆帕的压力下，在一系列氧逸度下进行。这项工作的动机是在喀斯喀特和墨西哥火山带的弧岩浆中推断出高喷发前含量（高达10 wt. % H2O）。对于前面的所有研究，我们将开发基于热力学的分析模型，以预测熔化/结晶的条件以及涉及H2O时产生的熔体成分。更广泛的影响：从这些研究中获得的信息将通过在专业期刊上发表而广泛传播。有关H2O的信息将引起地球动力学和矿物物理学界的广泛兴趣，并最终与地球海洋和地球上生命的起源有关。从这项研究中获得的实验专业知识将与实验社区的其他成员分享，预测温度、水含量和熔融/结晶压力的模型将被开发并分发给岩石学建模。本项目将培养研究生和本科生的实验岩石学/地球化学研究方法。这项研究将使他们能够参与实验的设计、执行和解释，这通常会为他们的科学生涯提供持续的动力和兴趣。

Intellectual Merit: Experiments are proposed to develop quantitative models of the effects of H2O on the temperature and pressure of melting in the uppermost mantle and fractional crystallization in the Earth's crust. The cycling of water through the Earth's interior is of fundamental importance for understanding the chemical evolution of the Earth over geologic time. The importance of H2O in igneous processes has been known for a long time, but experimental calibrations of the effects of H2O are few and far between. Such data are necessary for developing quantitative tools for estimating H2O abundances in magmas and understanding the influence of H2O on magmatic processes. To make progress new measurements are required on broad range of experimental projects.Three projects are proposed. 1) A systematic investigation of the influence of H2O on the liquidus of natural basaltic melts. These experiments will determine the effects of variable amounts of H2O on liquidus temperature. The experiments will form the basis for models of melting point lowering and help resolve the considerable uncertainty on the influence of small amounts of H2O on melting. 2) Investigation of the role of H2O, pressure and mantle composition on garnet peridotite melting. These experiments will provide quantitative estimates of the role played by H2O and mantle bulk composition (primarily the alkali elements Na2O and K2O) on the composition and temperature of magmas produced in subduction zone and sub continental mantle environments. 3) Experimental studies of the role of H2O and pressure on fractional crystallization of basaltic melts in the crust. In arc magmatic systems the compositional characteristics of differentiated arc magmas and their mineral assemblages provide evidence of the pre-eruptive H2O content, temperature and depth history of differentiation. Experimental studies of basalt and andesite magmas will be carried out at pressures of 300 to 800 MPa over a range of oxygen fugacities under H2O-saturated conditions. This work is motivated by the high pre-eruptive contents (up to 10 wt. % H2O) that have been inferred in arc magmas from the Cascades and Mexican Volcanic Belt. For all of the preceding studies we will develop thermodynamically based analytic models that allow prediction of conditions of melting/crystallization and compositions of melts generated when H2O is involved.Broader Impacts: The information derived from these studies will be broadly disseminated through publication in profrssional journals. The information on H2O will be of broad interest in the geodynamics and mineral physics community and ultimately has relevance for the origin of the Earth's oceans and life on Earth. The experimental expertise gained from this study will be shared with other members of the experimental community and models for predicting temperature, H2O content and pressure of melting/crystallization will be developed and distributed for petrologic modeling. This project will train graduate and undergraduate students in research methods of experimental petrology/geochemistry. The research will allow them to participate in the design, execution and interpretation of experiments, which often provides motivation and interest that lasts throughout their scientific career.