Collaborative Research: Density and structure of s

合作研究：密度和结构

• 批准号: 1620548
• 负责人: Yanbin Wang
• 金额: $ 33.6万
• 依托单位: University of Chicago
• 依托单位国家: 美国
• 项目类别: Continuing 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=1620548&HistoricalAwards=false
• 关键词: Collaborative; Research; Density; structure

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.

硅酸盐是地球外地壳和岩石地幔层的主要成分，在非常高的温度下熔化，尤其是在较深的地方。液态硅酸盐在地球的早期演化历史中发挥了关键作用，并继续影响着当今的动态过程。早期地球很可能在形成过程后熔化。当地球冷却时，液态硅酸盐凝固，并在冷却过程的各个阶段形成特定成分的晶体，从而定义了我们今天的地球的成分结构。大量岩浆从当今的洋中脊上升，这一过程与板块构造密切相关。这些岩浆的冷却产物形成了海底。全球各地的火山活动改变了环境并危及人类生命。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下硅酸盐液体的密度、粘度和结构。过去，获取此类知识的努力一直受到技术挑战的阻碍。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，用于研究高压和高温条件下硅酸盐液体的密度、压缩性和结构。这项研究将支持研究生和博士后的培训和指导，并将为早期职业科学家提供支持。 研究人员提出，通过结合使用大体积压力机和同步辐射的先进技术，研究 Na2O-CaO-MgO-FeO-Al2O3-SiO2 系统中选定成分的液体的结构-密度关系，以涵盖与深部地幔熔融相关的镁铁质至超镁铁质液体的主要成分。结构数据将在巴黎-爱丁堡压力机中以 20 GPa 和 2500 K 的压力收集。密度将使用原位 X 射线吸收和异位沉/浮技术来确定。为了补充密度测量，将在双级多砧压机中使用超声干涉测量法来测量选定的低粘度液体组合物的声速。利用这些数据，团队将在网络形成体（Si 和 Al）发生四面体到八面体配位变化的压力范围内检查结构与密度/压缩性之间的联系。这项工作将为模拟深部地幔条件下的液体压缩提供重要的实验约束，方法是：（1）通过覆盖上地幔、过渡带和下地幔顶部的压力范围内的配位变化，深入了解硅酸盐液体的结构演化；（2）通过液体中的配位转变获得密度和声速数据；（3）建立硅酸盐液体的新状态方程 结合结构信息，以便更好地预测深部地幔条件下的液体密度。