Collaborative Research: Density and structure of silicate liquids under deep mantle conditions

合作研究：深部地幔条件下硅酸盐液体的密度和结构

• 批准号: 1619964
• 负责人: James Van Orman
• 金额: $ 27.3万
• 依托单位: Case Western Reserve University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-07-01 至 2020-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1619964&HistoricalAwards=false
• 关键词: Collaborative; Research; Density; structure; silicate

Silicates, the major constituents of Earth's outer crust and rocky mantle layers, melt at very high temperatures, especially at deeper depths. Liquid forms of silicates played a pivotal role in the early evolution history of planet Earth and continue to influence dynamic processes in present day. The early Earth was most likely molten after the formation process. As the Earth cooled off, liquid silicates solidified and crystals of particular compositions formed at various stages of the cooling process, defining the composition structure of the Earth as we have today. Giant amounts of magmas are ascending from present-day mid-ocean ridges, a process closely related to plate tectonics. The cooling products of these magmas form the ocean floors. Volcanic activities over the globe change the environment and endangering human lives. Understanding the dynamics and thermodynamics of these processes requires knowledge of density, viscosity, and structure of silicate liquids over a wide range of pressure conditions corresponding to the Earth's interior. Efforts for obtaining such knowledge have been impeded by technical challenges in the past. To overcome the technical challenges, the investigators have developed a series of synchrotron-based techniques for studying density, compressibility, and structure of silicate liquids under high pressure and temperature conditions. This research will support the training and mentoring of a graduate student and post doc, and will provide support to early career scientists. The investigators propose to study structure-density relations of liquids with selected compositions in the system Na2O-CaO-MgO-FeO-Al2O3-SiO2 to cover major components of mafic to ultramafic liquids relevant to deep mantle melting, by combining advanced techniques using large-volume presses and synchrotron radiation. Structure data will be collected in the Paris-Edinburgh press to 20 GPa and 2500 K. Density will be determined using both in-situ X-ray absorption and ex-situ sink/float techniques. To complement density measurements, sound velocities of selected low-viscosity liquid compositions will be measured using ultrasonic interferometry in a double-stage multianvil press. With these data the team will examine the link between structure and density/compressibility across the pressure range where tetrahedral-to-octahedral coordination change of network formers (Si and Al) occurs. This work will provide vital experimental constraints on modeling liquid compression at deep mantle conditions, by (1) gaining insights into structural evolution of silicate liquids through coordination changes over the pressure range covering the upper mantle, transition zone, and the top of the lower mantle (2) obtaining data on density and acoustic velocity through the coordination transition in liquids, and (3) establishing new equations of state for silicate liquids incorporating structural information, to enable better prediction of liquid density under deep mantle conditions.

硅酸盐是地球外壳和岩石地幔层的主要成分，在非常高的温度下融化，尤其是在更深的深处。硅酸盐的液体形式在地球的早期进化史上起着关键作用，并继续影响当今的动态过程。在形成过程后，早期地球很可能是熔融的。随着地球的冷却，液体会在冷却过程的各个阶段形成的特定组成的固体和晶体，从而定义了地球的组成结构，就像我们今天一样。巨型岩浆正在从当今的中山山脊上升，这一过程与板块构造密切相关。这些岩浆的冷却产品形成了海地。全球的火山活动改变了环境并危及人类的生命。了解这些过程的动力学和热力学需要了解与地球内部相对应的各种压力条件上的密度，粘度和结构。过去的技术挑战阻碍了获得此类知识的努力。为了克服技术挑战，研究人员开发了一系列基于同步加速器的技术，用于研究在高压和温度条件下硅酸盐液体的密度，可压缩性和结构。这项研究将支持研究生和后DOC的培训和指导，并将为早期职业科学家提供支持。 研究人员建议研究液体与系统Na2o-Cao-Mgo-Feo-Al2o3-Sio2中所选成分的结构密度关系，以覆盖Mafic的主要成分与与深层熔化相关的超镁铁质液体，并通过使用大量volume Prastes和Synchrotrotron辐射结合先进技术。结构数据将在巴黎 - 埃德替恩堡出版社中收集到20 GPA和2500K。密度将使用原位X射线吸收和Ex-Situ水槽/浮点技术确定。为了补充密度测量，将在双阶段多阶段压机中使用超声干涉测量法测量选定的低粘度液体组成的声速。使用这些数据，团队将检查整个压力范围内的结构与密度/压缩性之间的联系，其中四面体到近二面体的协调变化发生了网络组合者（SI和AL）的变化。这项工作将通过（1）通过（1）了解硅酸盐液体的结构演变，通过在压力范围上的配位变化来对硅酸盐液体的结构演变进行建模，从而提供重要的实验限制。结合结构信息，以便在深幔条件下更好地预测液体密度。