Water in the Mantle: Effects of Hydration on Physical Properties of Mantle Minerals

地球地幔过渡带(400至670公里深度)矿物中水的重量百分之一大约等于地球表面上800米的液态水。地球海洋的体积确实有可能不是恒定的，而是通过与地幔固体硅酸盐相中以羟基形式储存的水进行动态交换而在整个地质时期保持不变的。组成上地幔和过渡带的名义上无水的硅酸盐矿物(顽辉石、橄榄石、水晶石和环杉石)可以包含高达几个重量百分比的H2O，在参考地球模型中的地震速度与软解石组成的过渡带中的水化作用(约1%)是一致的。这是一项研究含水顽辉石、橄榄石、水滑石、环木和钙钛矿相的稳定性、晶体化学和物理性质的建议，这些相可能出现在含水的上地幔和过渡带中，以改进对地球内部水分含量的估计。在巴伐利亚地质研究所(巴伐利亚地质研究所，BGI)的同事们的合作下，将合成一系列氢含量和镁/铁比的含水橄榄石、顽辉石、瓦兹利石、环木石和钙钛矿样品。样品将通过单晶X射线和中子衍射、电子探针、红外光谱、拉曼光谱和穆斯堡尔谱以及透射电子显微镜进行表征。等温可压缩系数将通过在科罗拉多大学的钻石顶压室中的单晶X射线衍射和在先进光子源上的同步加速器粉末衍射来测量。拟议研究的更广泛影响包括在一所远离美国主要矿物物理研究中心的大学培训实验室地球物理学的研究生和本科生，并向这些学生介绍APS等更大设施的实验。拟议的研究项目是对科罗拉多大学正在进行的野外观测地球物理项目(地震学)、地球物理模型和行星科学的补充。在美国学生和教师与德国拜罗伊特巴伐利亚地质研究所、牛津大学和ISIS中子衍射设施(英国)的科学家的合作中，该项目具有强大的和持续的国际组成部分。这项拟议研究的国内合作伙伴包括夏威夷大学和阿贡国家实验室的高级光子源(APS)。

One tenth of one weight percent H2O in the minerals of the Transition Zone of the Earth's mantle (400 to 670 km depth) is an amount roughly equal to 800 m. of liquid water over the surface of the planet. It is indeed possible that the volume of Earth's oceans has not been constant, but has been maintained through geologic time by a dynamic exchange with water stored as hydroxyl in the solid silicate phases of the mantle. The nominally anhydrous silicate minerals that make up the upper mantle and Transition Zone (enstatite, olivine, wadsleyite, and ringwoodite) can incorporate up to several weight percent H2O, and seismic velocities in reference Earth models are consistent with significant hydration (~1 percent by weight H2O) of wadsleyite and ringwoodite in a Transition Zone of pyrolite composition. This is a proposal to investigate the stability, crystal chemistry, and physical properties of hydrous enstatite, olivine, wadsleyite, ringwoodite, and perovskite phases that could occur in a hydrous upper mantle and Transition Zone in order to refine estimates of the water content of the Earth's interior. In collaboration with colleagues at the Bavarian Geological Institute (Bayerisches Geoinstitut, BGI), samples of hydrous olivine, enstatite, wadsleyite, ringwoodite and perovskite with a range of hydrogen contents and Mg/Fe ratios will be synthesized. Samples will be characterized by single-crystal X-ray and neutron diffraction, electron microprobe, IR, Raman, and Mossbauer spectroscopies, and transmission electron microscopy. Isothermal compressibilities will be measured by single-crystal X-ray diffraction in the diamond anvil cell at University of Colorado, and by synchrotron powder diffraction at the Advanced Photon Source. The broader impacts of the proposed research include training of graduate and undergraduate students in laboratory geophysics in a university that is distant from major centers of mineral physics research in the US and introducing these students to experiments at larger facilities such as APS. The proposed research project is complementary to on-going field observational geophysics programs (seismology), geophysical modeling and planetary sciences at the University of Colorado. The project has a strong and on-going international component of collaboration of US students and faculty with scientists at the Bavarian Geological Institute in Bayreuth, Germany, University of Oxford, and ISIS neutron diffraction facility (UK). Domestic collaborations of the proposed study include University of Hawaii and Advanced Photon Source (APS) at Argonne National Laboratory.