Collaborative Research: CSEDI: Understanding the Role of Hydrogen and Melting in the Water Transport Across the Transition Zone-Lower Mantle Boundary

该项目的目的是对地球深处的矿物性质进行新的实验和理论研究，这将有助于我们了解地球地幔中全球水循环的本质。不仅在地球表面，水（氢）也存在于地球内部，并在缓慢地循环。这种全球水循环创造并维持着地球上的海洋。根据过去几十年的一些研究，人们对地球内部浅层部分的水循环有了一个清晰的认识。然而，在地幔的最大部分，即下地幔中，水循环的性质仍然知之甚少。全球水循环的一个关键是融水的作用。融化将矿物质中的水分转移到熔体中，熔体进行长距离迁移，造成大规模的水运。然而，由于我们对地幔深部矿物中水分的认识有限，对地幔深部全球水循环的性质了解甚少。PI团队将汇集一套理论和实验方法来解决这些问题，并将在一个跨领域的研究项目中培训三所机构的研究生和本科生。ppi还将参与公众外展活动。本项目将在~660 km ~ ~1000 km深的下地幔浅层条件下测定桥菱岩（下地幔优势矿物）的水溶性，并研究水（氢）对桥菱岩电导率的影响。对桥菱石的清洁单晶进行实验研究，并利用红外光谱和SIMS对其氢含量和溶解度机理进行研究。电导率将测量这些样品的不同取向使用交流阻抗谱。第一性原理计算研究也将进行氢在菱镁石中的溶解度和迁移率，以帮助解释实验结果。这些结果将帮助我们开发一个全球水循环模型，并根据地球物理对水分布的估计来测试模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The aim of this project is to conduct new experimental and theoretical studies on the properties of mineral in the deep interior of Earth that will help us to understand the nature of global water circulation in Earth’s mantle. Not only on the surface, water (hydrogen) is present inside of Earth and slowly circulates. This global water circulation creates and maintains oceans on Earth. Based on a number of studies during the last a few decades, there is a clear idea about the water circulation in the shallow part of Earth’s interior. However, the nature of water circulation in the largest part of the mantle, the lower mantle, remains poorly constrained. A key in the global water circulation is the role of melting. Melting removes water from minerals to melt, and melt migrates a long distance to cause large-scale water transport. However, the nature of global water circulation in the deep mantle is very poorly understood mainly because our understanding of water in the minerals in the deep mantle is limited. The PI team will bring together a suite of theoretical and experimental methods to address these questions, and will train both graduate and undergraduate students at three institutions on a cross-cutting research project. The PIs will also engage in public outreach events.In this new project, the water solubility in bridgmanite (dominant lower mantle mineral) will be determined under the shallow lower mantle conditions from ~660 km to ~1000 km depth, and also the role of water (hydrogen) on electrical conductivity in bridgmanite will be investigated. Experimental studies will be made on clean single crystals of bridgmanite and the hydrogen content and solubility mechanisms will be studied using FTIR and SIMS. Electrical conductivity will be measured on these samples for different orientations using the AC impedance spectroscopy. First-principle computational studies will also be made on hydrogen solubility and mobility in bridgmanite to help interpreting the experimental results. These results will help us to develop a model of global water circulation and to test models against geophysical estimates of water distribution.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.