EAR-PF: Water in the Lower Mantle: Gaining Insight through Melt Generation and Deformation Textures

Vennari, Cara Elizabeth, Santa Cruz CA

Investigators

Abstract

Dr. Cara Vennari has been granted an NSF EAR postdoctoral fellowship to carry out research and education plans at the University of Chicago and the University of Utah. Water has been studied extensively in the upper mantle, where it has been shown to lower the melting temperature of mantle rock and weaken it; however, there has been less systematic study of water in the lower mantle. Using diamond anvil cells to generate high pressures during laboratory experiments, she will investigate the melting temperature and strength of lower mantle rock with a variety of water content to advance our understanding of hydrous silicate melts and explain local anisotropic regions of the lower mantle. Broader impacts of this work include its direct application to other Earth science disciplines (geodynamics, petrology, geophysics, planetary sciences and geochemistry), mentorship of younger students, and volunteering through outreach programs. The overall goal of this project is to understand the effect of water in the lower mantle. The first is high pressure melting of synthetic pyrolite composition, with the goals being to determine (with a range of water content) the melting temperature, explore the stable phases, and probe the melt and recrystallized products for the cation and hydrous distribution. Hydrous melts and mineralogy have been assumed to affect the rheologic character of the lower mantle properties; however, there have been no experimental evidence to support this, so the second type of experiment will be an axial stress experiment at lower mantle pressures to investigate the deformation of hydrous peridotite. Techniques used for the melting measurements include in situ powder diffraction coupled with ex situ SEM analysis. Strength measurements of hydrated lower mantle phases will be investigated using X-ray diffraction with radial geometry. 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.