Date of Award

Spring 1-1-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geological Sciences

First Advisor

Joseph R. Smyth

Second Advisor

Anne F. Sheehan

Third Advisor

Charles R. Stern

Abstract

The Earth's deep water cycle has been the object of significant debate in the mineral physics community. Many researchers have devoted their time and effort to investigate the mechanisms by which water may be transported and stored in the mantle. The bulk of this research has focused on the Mg2SiO4 polymorphs, olivine, wadsleyite, and ringwoodite, which have three cations to four oxygens (3:4) stoichiometry. There is however a significant fraction in the mantle having two cations to three oxygen (2:3) stoichiometry. In the upper mantle this fraction is composed of pyroxene and garnet, while in the transition zone the pyroxenes dissolve into the garnet phase. The majorite end-member is a pure magnesium silicate garnet that may dominate the garnet phase in the transition zone. Many previous studies have assumed that the hydration of this phase is negligible; however recent evidence suggests that the hydration of garnet may be significant. This study presents data collected on a hydrous mineral assemblage containing wadsleyite, ringwoodite, and majorite. There are very few poly-phase samples of this composition that have been synthesized, and analysis of this sample by electron probe microanalysis, Raman spectroscopy, and secondary ion mass spectroscopy has yielded valuable information on the partitioning of water and iron between these phases. The majorite has been analyzed by single crystal x-ray diffraction under both ambient and high pressure conditions. This study also presents an empirical seismic velocity model of the upper 1000 Km of Earth's mantle, with the goal of constraining the amount of hydrogen that may be sequestered in the transition zone.

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