Doctoral Dissertations

Date of Award

8-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Geology

Major Professor

Harry Y. McSween

Committee Members

Larry A. Taylor, Theodore C. Labotka, Robert N. Compton

Abstract

The planet Mars is geologically more similar to Earth than to other planets of the solar system. For the past 50 years, new rovers, orbital spacecraft, and new martian meteorites have helped us to understand the geological processes that occurred on Mars. In this dissertation, I investigate a wide range of martian igneous compositions, such as shergottite and nakhlite meteorites, Gusev and Gale surface basalts, and the Northwest Africa (NWA) 7034 breccia. I attempt to better understand magmatic processes that occurred in the martian mantle and crust as well as surficial processes using various petrologic and geochemical tools.

As shown by thermodynamical modeling, fractional crystallization of primary martian magmas can form a wide variety of magma compositions, including: tholeiitic and alkaline, under polybaric conditions.

Parental magmas of the most common martian meteorites, shergottites, appear to have undergone water-degassing, as judged from analyses of light-lithophile elements (Li, B, Be) with varying solubilities in exsolved aqueous fluids and Li isotopes, which can be fractionated by degassing. This magmatic water might have been a major source for martian surficial water during the Amazonian period.

In addition to shergottites, I examine the petrology of four Miller Range nakhlites, which, according to various petrological evidences, come from the same parent meteorite. However, modal abundances show that their parent meteorite was heterogeneous. Therefore, discovery of new nakhlites will be critical to fully understand stratigraphic differences in the nakhlite cumulate pile.

Finally, I show that one unusual vitrophyric clast in the NWA 7034 polymict martian breccia is likely an impact melt whose parent rock has the same composition as the Humphrey Gusev basalt, and represents the first martian sample with a similar composition to surface rocks measured by rovers.

I demonstrate in this dissertation that there is a wide variety of martian igneous compositions and that the study of these compositions and recovery of new martian meteorites and analyses of martian surface basalts by rovers is critical to understanding crustal and mantle petrologic processes on Mars.

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