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

Louisiana State University, Baton Rouge LA

Investigators

Abstract

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.