Date of Award

Spring 1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geological Sciences

First Advisor

Brian M. Hynek

Second Advisor

Lang Farmer

Third Advisor

Tom McCollom

Fourth Advisor

Alexis Templeton

Fifth Advisor

Steve Schmidt

Abstract

Acid-sulfate alteration is a dominant weathering process in high temperature, low pH, sulfur-rich volcanic environments. Additionally, hydrothermal environments have been proposed as locations where life could have originated on Earth. Based on the extensive evidence of flowing surface water and persistent volcanism, similar locations and processes could have existed on early Mars. Globally observed alteration mineral assemblages likely represent relic Martian hydrothermal settings. Yet the limited understanding of environmental controls, limits the confidence of interpreting the paleoconditions of these hydrothermal systems and assessing their habitability to support microbial life. This thesis presents a series of laboratory experiments, geochemical models, analog fieldwork, and Martian remote sensing to characterize distinguishing features and controls of acid-sulfate alteration. The experiments and models were designed to replicate alteration is a highly acidic, sulfurous, and hot field sites. The basaltic minerals were individually reacted in both experimental and model simulations with varying initial parameters to infer the geochemical pathways of acid-sulfate alteration on Earth and Mars. It was found that for a specific starting material, secondary mineralogies were consistent. Variations in pH, temperature and duration affected the abundance, shape, and size of mineral products. Additionally evaporation played a key role in secondary deposits; therefore, both alteration and evaporitic processes need to be taken into consideration. Analog volcanic sites in Nicaragua were used to supplement this work and highlight differences between natural and simulated alteration. In situ visible near-infrared spectroscopy demonstrated that primary lithology and gas chemistry were dominant controls of alteration, with secondary effects from environmental controls, such as temperature and pH. The spectroscopic research from the field was directly related to Mars observations in Noctis Labyrinthus, Terra Sirenum, Syrtis Major, and Mawrth Vallis to help interpret ancient conditions in those settings. To further apply the results from experiments, models, and fieldwork, Coprates Chasma in eastern Valles Marineris was studied using mineralogical and morphological data. Emplacement of alteration minerals indicated both pre- and post-rifting hydrothermal activity. Smaller southern grabens appeared to have experienced a unique alteration. In summary, this dissertation presents research that contributes to the understanding of the geological evolution of Mars and potentially habitability.

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