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

职业：水合作用对从原子到地球物理尺度的地幔物质物理性质的影响

• 批准号: 0748707
• 负责人: Steven Jacobsen
• 金额: $ 50.93万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-01-01 至 2013-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0748707&HistoricalAwards=false
• 关键词: CAREER; Effects; Hydration; Physical; Properties

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.

该项目从原子尺度到地球物理尺度考察了硅酸盐矿物在地球深水循环中的作用。在400-700 km深度的模拟地幔条件下，一些矿物以羟基（OH）的形式吸收水分的能力显著，导致其物理性质发生改变。实验研究将集中于确定水化作用对高压下地球材料行为的影响。研究结果将提供地幔水化的地球物理指标，为利用地震波远程探测地幔深部水提供便利。研究生和本科生的研究将利用PI开发的新的实验室超声技术。学生将有机会在两个不同的国家实验室使用同步加速器光源在大型设备上进行实验。学生将与更广泛的地球物理团体和公众利益接触，帮助解释在地幔中观测到的神秘结构，这些结构可能与水有关。当地K-12教育活动的重点是通过美国西北大学（Northwestern University）和埃文斯顿65学区（Evanston School District 65）合作的EXCITE项目，缩小少数族裔在科学成就方面的差距。EXCITE项目是一个纵向项目，招收少数族裔三年级学生参加为期六年的项目，其中包括定期访问地球和行星科学系。PI将领导演讲和实践演示，以鼓励他们对地球科学的兴趣，并最终导致埃文斯顿镇高中的高级课程和荣誉科学课程中少数民族学生的入学率增加。在类地行星中，地球是独一无二的，它的表面保留着大量的液态水。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水库，并作为全球动态水循环的一部分。实验岩石学的结果表明，在660公里深处的地幔中，按重量计有可能含有百分之零点几的水，相当于海洋体积的液态水。然而，地球化学证据表明岩浆源区相对干燥。深层水循环和储存的真实程度基本上是未知的，等待矿物物理学和地震学的进一步限制。该奖项旨在解决深层地幔水化作用的广泛影响，并为含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低浓度的氢会影响地球材料的性质。在介孔尺度上，h扩散将使用一套新的宝石级含水地幔相单晶样品进行研究，该样品由PI和学生在德国拜罗伊特bayerhes地质研究所的5000吨多砧压机中培养。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s波速度异常，例如最近在美国东部探测到的s波速度异常。