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部矿物的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性质。水(氢)不仅存在于地球表面，还存在于地球内部，并缓慢循环。这种全球水循环创造并维持着地球上的海洋。基于过去几十年的大量研究，人们对地球内部浅层的水循环有了一个清晰的概念。然而，地幔最大部分--下地幔中的水循环的性质仍然没有得到很好的约束。全球水循环中的一个关键是融化的作用。熔融使矿物中的水分融化，熔体长距离迁移，造成大规模的水分输送。然而，对全球深部地幔水循环的性质了解很少，主要是因为我们对深部地幔矿物中的水的了解有限。PI团队将汇集一套理论和实验方法来解决这些问题，并将对三个机构的研究生和本科生进行交叉研究项目的培训。在这个新的项目中，将在~660公里到~1000公里深的浅层下地幔条件下测定桥辉橄榄石(主要是下地幔矿物)中的水的溶解度，并将研究水(氢)对桥辉橄榄石的电导率的作用。对纯净的桥锰矿单晶进行了实验研究，并用FTIR和SIMS对其氢含量和溶解机理进行了研究。将使用交流阻抗谱测量这些不同取向的样品的电导率。为了解释实验结果，我们还将对氢在钠镁橄榄石中的溶解度和迁移率进行第一性原理计算研究。这些结果将有助于我们开发全球水循环模型，并针对水分布的地球物理估计对模型进行测试。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.