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研究硅酸盐矿物在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，一些矿物具有以羟基（OH）形式吸收水的显着能力，从而导致物理性质发生改变。实验研究将侧重于确定水合作用对高压下地球材料行为的影响。结果将提供地幔水合作用的地球物理指标，有助于利用地震波远程检测地幔深处的水。研究生和本科生研究将利用 PI 开发的新实验室超声波技术。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施中进行实验。学生将与更​​广泛的地球物理界和公众利益互动，帮助解释在地幔地震中观察到的神秘结构，这些结构可能与水有关。当地 K-12 活动的重点是通过 EXCITE 项目缩小少数族裔科学成就差距，EXCITE 项目是西北大学和埃文斯顿学区 65 之间的合作伙伴关系。EXCITE 项目是一项纵向计划，招收少数族裔三年级学生参加为期六年的项目，其中包括常规项目参观地球与行星科学系。 PI 将主持演讲和实践演示，鼓励他们对地球科学的兴趣，并最终提高少数族裔学生在埃文斯顿镇高中的先修课程和荣誉科学课程的入学率。地球在地球上的类地行星中是独一无二的。在其表面维持大量液态水。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。实验岩石学结果表明，在深达 660 公里的地幔中，可能含有重量百分比为百分之几的 H2O，相当于海洋液态水的体积。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，有待矿物物理学和地震学的进一步限制。该职业奖解决了深部地幔水合作用的更广泛影响，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了新的机会。在原子尺度上，氢位置和弹性特性的确定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特性。在细观尺度上，将使用一套新的宝石级含水地幔相单晶样品套件来研究 H 扩散，这些样品套件是由 PI 和学生在德国拜罗伊特 Bayerishes Geoinstitut 的 5000 吨多砧压机中生长的。将通过原位技术研究水合作用对相变的影响。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横波速度异常，例如最近在美国东部下方检测到的异常。