Collaborative Research: Density and structure of s

硅酸盐是地球外壳和岩石地幔的主要成分，在非常高的温度下熔化，特别是在更深的地方。液态硅酸盐在地球早期演化史中发挥了关键作用，并继续影响着当今的动力学过程。早期的地球很可能是在形成过程之后熔化的。随着地球的冷却，液态硅酸盐在冷却过程的不同阶段凝固并形成特定组成的晶体，定义了我们今天所拥有的地球的组成结构。大量的岩浆正在从今天的大洋中脊上升，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洋底。全球各地的火山活动改变了环境，危及人类生命。要了解这些过程的动力学和热力学，需要在与地球内部相对应的广泛压力条件下了解硅酸盐液体的密度、粘度和结构。过去，获取此类知识的努力因技术挑战而受阻。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、可压缩性和结构。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。研究人员建议，通过结合使用大容量压力机和同步辐射的先进技术，研究Na2O-CaO-MgO-FeO-Al_2O_3-SiO_2系统中选定成分的液体的结构-密度关系，以涵盖与地幔深部熔融有关的镁铁质到超镁铁质液体的主要成分。结构数据将在巴黎-爱丁堡出版社收集到20 Gpa和2500K，密度将使用原位X射线吸收和非原位沉浮技术来确定。为了补充密度测量，选定的低粘度液体成分的声速将在双级多顶锤压力机中使用超声波干涉法进行测量。有了这些数据，研究小组将在压力范围内检查结构和密度/可压缩性之间的联系，在压力范围内，网络形成物(Si和Al)发生四面体到八面体的配位变化。这项工作将通过以下方式为模拟深部地幔条件下的液体压缩提供重要的实验约束：(1)通过覆盖上地幔、过渡区和下地幔顶部的压力范围的协调变化来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关于密度和声速的数据；以及(3)建立包含结构信息的硅酸盐液体的新的状态方程，以便能够更好地预测深部地幔条件下的液体密度。

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.