Earth and Planetary Sciences ETDs

Publication Date

Summer 7-29-2019

Abstract

The 410-discontinuity separating the uppermost mantle from the transition zone is commonly believed to be caused by the olivine-wadsleyite transformation. However, the velocity change at the 410-discontinuity predicted by the standard pyrolitic model is not completely consistent with the seismic observations, leading to questions about the accuracy of the seismic models, or uncertainties of the mineral physics predictions. More regional seismic observations suggest that the depth, sharpness, and velocity jumps at the 410-discontinuity are different at different places, caused by thermal and/or compositional heterogeneities in the upper mantle. To explain the inconsistencies between the mineral physics and seismic models and constrain the composition, temperature and pressure conditions in the mantle, a thorough study on the elastic properties of relevant phases, especially wadsleyite at high-pressure condition is needed. As the major hydrogen-bearing mineral in the transition zone, the single-crystal elastic properties of hydrous Fe-bearing wadsleyite high-pressure condition is controversial. In this study, I used in-situ Brillouin spectroscopy combined with diamond anvil cell (DAC) technique to measure the elastic properties of a Fe-bearing wadsleyite sample up to 18GPa, at ambient-temperature condition. The bulk (KS) and shear (G) moduli are 164(1) GPa and 104.5(4) GPa respectively. Higher KS’ is obtained by this study as 4.7(2) compared with previous studies. The G’=1.62(4) is identical to the one obtained by a previous study on the wadsleyite with similar chemical composition. The hydrogen in the wadsleyite can soften the KS and G at ambient condition, but the effect diminishes at higher pressures due to the larger KS’ and G’ for hydrous samples. In addition, the anisotropy of wadsleyite decreases dramatically with increasing H2O content and increases with Fe content.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Jin Zhang

Second Committee Member

Brandon Schmandt

Third Committee Member

Charles Shearer

Language

English

Document Type

Thesis

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