CAREER: Effects of Hydration on the Physical Properties of Mantle Materials from Atomic to Geophysical Scales

该项目研究了硅酸盐矿物在从原子到地球物理尺度的地球深水循环中的作用。在400-700公里深度的模拟地幔条件下，某些矿物以羟基(OH)的形式具有显著的吸水能力，从而导致物理性质的改变。实验研究的重点将是确定水合作用对地球材料在高压下行为的影响。这些成果将提供地幔水化的地球物理指标，有助于利用地震波远程探测地幔深处的水。研究生和本科生的研究将利用PI开发的新的实验室超声波技术。学生们将有机会在两个不同的国家实验室使用同步辐射光源在大型设施中进行实验。学生将与更广泛的地球物理界和公众兴趣接触，帮助解释在地幔中通过地震观测到的神秘结构，这些结构可能与水有关。当地的K-12活动侧重于通过西北大学和埃文斯顿第65学区的合作项目Excite缩小少数族裔的科学成就差距。Excite项目是一个纵向项目，招募少数族裔三年级学生参加一个为期六年的项目，定期访问地球和行星科学系。PI将领导演讲和动手演示，以鼓励他们对地球科学的兴趣，并最终将导致埃文斯顿镇高中高级选修和荣誉科学课程的少数民族学生人数增加。地球在地球表面保持着巨大的液态水水库方面是独一无二的。地幔的固体硅酸盐矿物有可能在地球内部储存另一个主要的H2O储藏库，并作为动态全球水循环的一部分。实验岩石学的结果表明，在660公里深的地幔中，可能含有十分之几重量百分比的H2O，相当于海洋体积的液态水当量。然而，地球化学证据表明，岩浆源区相对干燥。深水循环和储存的真实范围基本上是未知的，并等待矿物物理和地震学的进一步限制。这一职业奖涉及深部地幔水化作用的更广泛影响，并旨在为含OH地幔硅酸盐矿物的结构和物理性质的实验研究提供新的机会。在原子尺度上，确定氢的位置和弹性性质将有助于理解为什么相对较低浓度的氢会影响地球材料的性质。在介观尺度上，将使用一套新的宝石质量的含水地幔相单晶样本来研究氢扩散，该单晶是由PI和学生在德国拜罗伊特拜尔里斯地质研究所5000吨多砧板压力机上生长的。将用原位技术研究水化对相变的影响。最后，实验数据将与热弹性模型相结合，以解释地震层析成像报告的神秘的S波速异常，例如最近在美国东部地下探测到的那个。

This project examines the role of silicate minerals in Earth's deep water cycle from atomic to geophysical scales. Under simulated mantle conditions of 400-700 km depth, some minerals have a remarkable ability to absorb water as hydroxyl (OH), resulting in modified physical properties. Experimental studies will focus on determining the effects of hydration on the behavior of Earth materials at high pressures. Results will provide geophysical indicators of mantle hydration that facilitate detection of water in the deep mantle remotely using seismic waves. Graduate and undergraduate research will capitalize on new laboratory ultrasonic techniques developed by the PI. Students will have the opportunity to lead experiments at large-scale facilities using synchrotron-light sources at two different national laboratories. Students will interface with the broader geophysical community and public interest in aiding interpretation of enigmatic structures observed seismically in the mantle, which may be related to water. Local K-12 activities focus on closing the minority science achievement gap through Project EXCITE, a partnership between Northwestern University and Evanston School District 65. Project EXCITE is a longitudinal program, which recruits minority third-grade students for a six-year program involving regular visits to the Department of Earth and Planetary Sciences. The PI will lead presentations and hands-on demonstrations that encourage their interest in Earth science, and will ultimately lead to increased enrollment of minority students in advanced-placement and honors science courses at Evanston Township High School.Earth is unique among the terrestrial planets in maintaining a large reservoir of liquid water on its surface. The solid silicate minerals of the mantle have the potential to store another major reservoir of H2O inside the Earth and act as part of a dynamic global water cycle. Results from experimental petrology have shown that it is possible to contain several tenths of a percent H2O by weight in the mantle down to 660-km depth, equal to ocean volumes of liquid-water equivalent. However, geochemical evidence suggests that magma source regions are relatively dry. The real extent of deep water cycling and storage is essentially unknown and awaits further constraints from mineral physics and seismology. This CAREER award addresses the broader implications of deep-mantle hydration and targets new opportunities for experimental studies on the structures and physical properties of OH-bearing mantle silicate minerals. At the atomic scale, determination of hydrogen positions and elastic properties will advance understanding of why relatively low concentrations of hydrogen influence the properties of Earth materials. At the mesoscopic scale, H-diffusion will be studied using a new sample suite of gem-quality single-crystals of hydrous mantle phases, grown by the PI and students in the 5000-ton multi-anvil press at Bayerishes Geoinstitut in Bayreuth, Germany. The effects of hydration on phase transformations will be studied with in-situ techniques. Finally, experimental data will be combined with thermoelastic modeling to interpret enigmatic S-wave velocity anomalies reported from seismic tomography, such as the one recently detected beneath the eastern US.