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Date of Award

Spring 2025

Document Type

Masters Thesis

Department or Program Affiliation

Geology

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Boujibar, Asmaa

Second Advisor

Anzures, Brendan

Third Advisor

Mulcahy, Sean

Abstract

Mercury’s distinct geochemistry, characterized by its low FeO content and elevated sulfur concentrations suggests that it underwent a unique differentiation process under highly reduced conditions. These conditions promote the formation of unusual sulfides, such as calcium- and magnesium-bearing phases. Understanding the stability and composition of these sulfides is crucial to reconstructing Mercury’s differentiation. To investigate this, high-pressure, high temperature (HPHT) experiments were conducted on synthetic compositions designed to simulate Mercury’s magma ocean (MMO) post core formation. These experiments replicated Mercury mantle-like conditions (1 GPa, 1500-1700 ÅãC, Δ𝐼𝑊-9.8 to -5.5) to determine sulfur concentration in the silicate melt at sulfide saturation (SCSS) and the partitioning behavior of Ca and Mg between the sulfide and silicate phase. By combining experimental data with thermodynamic modeling, this study explores how temperature, pressure, oxygen fugacity and composition influence the formation and stability of calcium- and magnesium-rich sulfides and the implications it has on Mercury’s differentiation.

The combined experimental and modeling results demonstrate that calcium and magnesium partitioning, along with sulfur concentration in the silicate melt at sulfide saturation, are highly sensitive to oxygen fugacity, pressure, temperature and composition. The formation of Ca- and Mg- rich sulfides under Mercury-like conditions suggests that these phases could influence mantle crust differentiation, with sulfides in equilibrium with the low magnesium northern plain (N-LMg) terrane containing up to 12.5 wt.% Ca and 11.7 wt.% Mg. Together, these findings advance our understanding of Mercury’s unique geochemical evolution and provide a framework for exploring sulfide behavior in other reduced planetary bodies.

Type

Text

Keywords

Mercury, Sulfide saturation, Oxygen fugacity, Thermodynamic modeling, Planetary differentiation

Publisher

Western Washington University

OCLC Number

1521416663

Subject – LCSH

Mercury (Planet)--Geology; Sulfides; Thermodynamics; Mineralogy

Geographic Coverage

Mercury (Planet)

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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