Exploring Anisotropy in the Deep Earth

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Large regions of the Earth are anisotropic for propagation of seismic waves, which are waves that propagate at different speeds in different directions. Anisotropy is present in the crust, in the upper mantle, particularly subduction zones, in the lower mantle mainly the lowermost zone, and the inner core. The detailed mechanisms that produce the crystal alignments that lead to anisotropy in the deep Earth are still poorly understood. This project will conduct experiments and modeling of high pressure and temperature to explore the processes by quantitative analysis of preferred orientation patterns of crystals that form at deep Earth conditions. The project will provide data that are critical for interpreting macroscopic seismic observations. But the methods in synchrotron diffraction that will be developed, as well as advanced methods of data analysis, are also relevant for a broad range of physical sciences. The experimental as well as modeling methodologies that are developed will be made available to other researchers. They will be promoted through publications, workshops, training and distribution of software. The research will fund the research of a PhD student. The primary goal of this project is to advance understanding of mechanisms that are active during geodynamic convection. Plastic deformation has been largely attributed to dislocation creep but other mechanisms are likely to play an important role, particularly dynamic recrystallization. This project will explore new methods such as synchrotron multigrain crystallography to study nucleation and grain growth in situ at lower mantle conditions. The outcomes of these experiments on lower mantle minerals such as ringwoodite, bridgmanite, ferropericlase and postperovskite will be used to model anisotropy in a convective lower mantle. Contrary to previous models that relied on dislocation glide, this work will include recrystallization and also investigate the influence of preferred crystal alignment on dynamic flow. 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.