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

智力上的优点。氢可能是地球主体中最不受约束的组成变量，它在压力下的地球化学行为也鲜为人知。在低压下(5 Gpa)，它是高度不相容的，但它在地幔矿物中的配伍性随着压力(深度)的增加而增加，因此它在名义上无水的硅酸盐中的溶解度增加到更深的上地幔和过渡带的百分比水平。在这种浓度下，它对这些矿物的弹性性质有重大影响，因此有可能从地震研究中探测到这些地区是否存在水合作用。该项目旨在合成和测量名义上无水高压硅酸盐的含水变体的单晶样品的物理性质，并测量可用于限制氢在地幔中的作用的性质。从以前的多砧板实验中收集了50多个样品进行研究。此外，还将在德国拜罗伊特的拜尔里斯地质研究所使用1200吨和5000吨压力机进行绿辉石、瓦德利石II和钙钛矿的协同合成实验。用单晶X射线衍射法测量水化对镁橄榄石、瓦兹利石和环木石晶体结构和压缩性能的影响，并为用布里渊光谱测量弹性性能提供定向的、有特征的样品。利用单晶X射线衍射仪，在室温和100~600K的温度下，测量了水化作用对橄榄石、水滑石、环辉石和顽辉石热膨胀的影响。通过粉末或单晶同步加速器衍射测量高温可压缩性的探索性实验将与夏威夷大学的研究小组合作进行。这些材料中的质子位置将由ISIS(牛津，英国)或SNS(橡树岭)的单晶中子衍射进行研究。主要目标是提供矿物物理学对地幔中氢的数量和作用的限制。这项研究将促进广泛的机构间和国际合作，并在广泛的科学领域交流思想和技术。该项目还将包括本科生和研究生参与研究，作为PI教学计划的组成部分。

Intellectual merit. Hydrogen is perhaps the most poorly constrained compositional variable in the bulk Earth, and its geochemical behavior at pressure poorly understood. At low pressures (5 GPa) it is highly incompatible, but its compatibility in mantle minerals increases with pressure (depth) so that its solubility in nominally anhydrous silicates increases to percent levels in deeper upper mantle and transition zone. At such concentrations it has a significant effect on elastic properties of these minerals so that it may be possible to detect the presence of hydration in these regions from seismic studies.This project aims to synthesize and measure physical properties of single-crystal samples of hydrous variants of nominally anhydrous high pressure silicates and to measure properties that can be used to constrain the role of hydrogen in the Earth's mantle. A collection of over 50 samples from previous multi-anvil experiments is available for study. Also, collaborative synthesis experiments on omphacite, wadsleyite II, and perovskite will be conducted using 1200 and 5000 ton presses in at Bayerisches Geoinstitut in Bayreuth, Germany. The effects of hydration on the crystal structure and compressibility of forsterite, wadsleyite and ringwoodite will be measured by single crystal X-ray diffraction and oriented, characterized samples will be provided for measurement of elastic properties using Brillouin spectroscopy. The effect of hydration on thermal expansion of olivine, wadsleyite, ringwoodite, and enstatite will be measured at room pressure and temperatures of 100 to 600 K by single crystal X-ray diffraction. Exploratory experiments to measure compressibility at high temperature by powder or single-crystal synchrotron diffraction will be conducted in collaboration with the group at University of Hawaii. Proton positions in these materials will be investigated by single-crystal neutron diffraction at ISIS (Oxford, UK) or SNS (Oak Ridge). The major objective is to provide constraints from mineral physics on the amount and role of H in the Earth's mantle.Broader impacts. This research will promote extensive inter-institutional and international collaboration and result in exchange of ideas and technology across a broad scientific spectrum. This project also will involve undergraduate and graduate in research as an integral part of the PI's teaching program.