Hydration State of the Transition Zone and Lowermost Mantle

过渡带和最低地幔的水合状态

• 批准号: 1452344
• 负责人: Steven Jacobsen
• 金额: $ 34.35万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1452344&HistoricalAwards=false
• 关键词: Hydration; State; Transition; Zone; Lowermost

The global water cycle is connected to the Earth's deep interior through plate tectonics. Hydrous minerals within oceanic crust carry the components of water (H2O) into the mantle at convergent plate boundaries, having influence on melt generation and volcanism as part of a cycle that returns H2O to the surface repeatedly over geologic time. How deeply the water cycle extends into the Earth's mantle is not known. However, evidence is mounting that certain mantle minerals such as ringwoodite, found in a layer called the transition zone (410-660 km depth), may contain a significant -if not the largest- geochemical reservoir of H2O in the planet. The presence of just a few weight percent H2O bound in minerals of the transition zone would constitute more water than is present in the oceans. Determining the scale and distribution of H2O in the mantle has implications for understanding the geochemical water cycle, deep melt generation, and determining the Earth's composition and origin of Earth's water.This study combines mineral physics experiments on laboratory-grown, hydrated mantle materials at high pressures and high temperatures with new and forthcoming regional seismic studies emanating from NSF's Earthscope (USArray) to constrain the scale and distribution of water in the Earth's mantle transition zone. At deep mantle conditions, water is no longer found in the familiar liquid form, but rather bound as hydroxyl (OH) through charge-coupled chemical substitutions in the crystal structure of high-pressure silicates. Hydrous melts may also be present at depths where the H2O storage capacity of minerals such as bridgmanite is relatively low. Experimental techniques including GHz-ultrasonic interferometry at Northwestern University and Brillouin scattering at the Advanced Photon Source, Argonne National Laboratory, will be employed to measure the influence of hydration on the elastic properties of mantle minerals such as wadsleyite, ringwoodite, and majoritic garnet, as well as on silicate glasses. Those results will be used to build a publically-available thermoelastic database, which provides input such as elastic moduli and their pressure-temperature derivatives needed to forward model expected seismic velocities in the mantle as a function of depth, temperature, and water content. Combined with observations from regional-scale seismic studies of the mantle, the results will be used to infer the mantle hydration state beneath North America and more globally as high-resolution seismic data become available.

全球水循环通过板块构造连接到地球深内部。海洋壳中的含水矿物在收敛板边界处将水的成分（H2O）带入地幔中，对熔体的产生和火山症影响，这是循环的一部分，该循环在地质时间内反复返回H2O。尚不清楚水周期延伸到地球地幔中的深度。但是，有证据表明，某些地幔矿物（例如Ringwoodite）在一个称为过渡区（410-660 km深度）的层中发现的，如果不是地球中H2O的最大的地球化学储层，则可能包含重要的。在过渡区的矿物质中，H2O仅有几个重量百分比的存在将构成比海洋中的水更多的水。确定地幔中H2O的规模和分布对理解地球化学水周期，深层产生以及确定地球水的组成和起源。这项研究结合了矿物质物理学实验，将实验室成长的，水分的地幔材料与高温和高温和即将到来的区域的渗透率与n seasis seration squartions squartions squartians n s seragion serage n s n s n s squales一起进行，在地球地幔过渡区。在深陆壁条件下，不再以熟悉的液体形式发现水，而是通过高压硅酸盐晶体结构中的电荷耦合化学取代为羟基（OH）。含水熔体也可能存在于矿物质（例如Bridgmanite）的H2O存储能力相对较低的深度。西北大学的GHz-硫代干涉仪和高级光子源的Brillouin散射，Argonne National Laboratory的实验技术将用于衡量水合对Wadsleyite矿物质（如Wadsleyite，Ringwoodite，Ringwoodite，Ringwoodite和Mapior Itic garnet）等地幔矿物质的影响。这些结果将用于构建公共可用的热弹性数据库，该数据库提供了弹性模量及其压力温度衍生物等输入，以将地幔中预期的地震速度转发为深度，温度和水含量的函数。结合从地幔区域尺度的地震研究的观察结果，结果将用于推断北美下面的地幔水合状态，并且随着高分辨率地震数据的可用性，全球范围更大。