Award Date

8-31-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geoscience

First Committee Member

Elisabeth M. Hausrath

Second Committee Member

Joel Hurowtiz

Third Committee Member

Oliver Tschauner

Fourth Committee Member

Arya Udry

Fifth Committee Member

Paul Forster

Number of Pages

279

Abstract

This dissertation is comprised of three studies investigating clay mineralogy on, or near the martian surface, with an introductory chapter, introducing and linking the three studies. Chapter two is on the subject of clay mineral synthesis, including Fe/Mg clay minerals which have been detected at multiple locations across the southern highlands. These Fe/Mg clay minerals have been previously interpreted as forming in anoxic/reducing environments, conducive to the preservation of organic matter. The results of this study suggest that the previous interpretation of Fe/Mg-rich clay as requiring anoxic/reducing conditions may not be accurate, as the minor presence of Mg (below what is found in many naturally occurring nontronites) allowed for the rapid precipitation of Fe-rich clay minerals under oxidized conditions. These results would prompt a reinterpretation of clay-bearing environments on the martian surface and may explain the relative dearth of detectable organic carbon on Mars.

Chapter three is on the subject of nontronite dissolution kinetics and its implications for Mars. Nontronite is a Fe-rich smectite and has been identified on the martian surface with orbital Visible Near InfraRed (VNIR) spectrometers. The results of this study suggest nontronite is stable relative to the primary minerals in basalt under acidic and oxidizing conditions and once formed may remain on the martian surface for significant durations. Nontronite dissolution is more rapid than other clay minerals, such as kaolinite and montmorillonite (under acidic and oxidizing conditions). These results suggest the dissolution of mixed clay units may produce stratigraphy (e.g. Al-rich clay minerals overlying Fe/Mg-rich phyllosilicates) similar to that observed in the Mawrth Vallis region and other localities on the martian surface and may therefore imply surficial weathering.

In chapter four, reactive transport modeling was applied to investigate potential weathering profiles detected at, or near the martian surface. These result suggest that when Fe/Mg rich clay minerals are exposed to pedogenic conditions they alter to montmorillonite and kaolinite (i.e. the Al-rich overlying layer). The models included four scenarios where the parent materials consisted of: nontronite; nontronite and montmorillonite; nontronite and saponite and pure saponite. In all scenarios and in all cases (i.e. regardless of temperature, pH and flow rate) the weathering of the parent material resulted in the precipitation of an Al-rich layer. Similar stratigraphy has been observed in the Mawrth Vallis region and other localities on the martian surface. These results would suggest that the observed transitions in clay mineral chemistry are the result of weathering, implying the surface of Mars may have been exposed to long-term liquid water at its surface.

Keywords

Clay; Life; Mars; Nontronite; Soil; Weathering

Disciplines

Geochemistry | Geology | Mineral Physics

Language

English

Available for download on Friday, August 31, 2018


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