Thermodynamic Measurements and Phase Equilibria of High-Pressure Silicates

需要资金来测量选定的高压地幔硅酸盐的低温热容。热容是一个基本的热力学参数，直到最近还不可能在低温下对小体积的合成材料进行测量。所需矿物相的合成将在多砧板设备中进行，低温热容测量将使用物理性质测量系统进行。热容测量将在几个地幔阶段进行，包括高压多晶型橄榄石和长石。这些测量将允许从现有的焓测量和/或实验相平衡中产生这些相和相关相的吉布斯自由能。这项研究的结果有望阐明地幔组合的稳定性，并将允许计算在俯冲和大陆碰撞期间变质的高压岩石的新相图。为了更深入地了解越来越多的已知岩石在造山事件或火山爆炸作用期间达到超高压并返回地表，需要对新的反应进行评估，这项研究将对此做出重大贡献。这项工作有助于更广泛地了解地球深部的基本构造过程。以前对地幔组合的研究基于许多简化，包括相对简单的成分。膨胀的组成系统更接近于真实的地幔和在那里产生的火山岩。未来对这类复杂系统的研究取决于对重要地幔矿物的热力学和相平衡的透彻了解，包括这一提议中所探讨的那些。相平衡对地幔的结构和动力学提供了重要的约束，地幔是绝大多数火山岩和许多大地震的来源。

Funding is requested to measure the low-temperature heat capacities of selected high-pressure mantle silicates. Heat capacity is a fundamental thermodynamic parameter that until recently has been impossible to measure at low temperatures on small volumes of synthetic material. Synthesis of the desired mineral phases will be conducted in a multi-anvil apparatus and low-temperature heat capacity measurements will be conducted with a Physical Properties Measurement System. Heat capacity measurements will be carried out on several mantle phases, including high-pressure polymorphs of olivine and feldspar. These measurements will allow generation of the Gibbs free energies of these and associated phases from the extant enthalpy measurements and/or experimental phase equilibria. Results of this study are expected to shed light on the stability of assemblages in the mantle and will allow calculation of new phase diagrams for high-pressure rocks that are metamorphosed during subduction and continental collision. A deeper understanding of the increasing number of rocks known to have reached ultrahigh pressures and returned to the surface during mountain-building events or explosive volcanic action requires the evaluation of new reactions, to which this study will contribute materially. This work contributes to a broader understanding of fundamental tectonic processes in the deep Earth. Previous studies of mantle assemblages have been based on many simplifications, including relatively simple compositions. Systems of expanded composition more closely represent the real mantle and the volcanic rocks that are generated there. Future study of such complex systems is dependent on a thorough knowledge of the thermodynamics and phase equilibria of important mantle minerals including those explored in this proposal. The phase equilibria provide important constraints on the structure and dynamics of the mantle, which is the source for the great majority of volcanic rocks and for many major earthquakes.