Date of Award

Spring 1-1-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Brian M. Hynek

Second Advisor

Thomas McCollom

Third Advisor

Alexis Templeton

Fourth Advisor

Raina Gough

Fifth Advisor

Stephen Mojzsis

Abstract

Hydrothermal acid-sulfate alteration is a common process in volcanic systems on Earth, and it may be inferred that this process played an important role in Mars’ geologic history as well. Several areas have been identified on Mars with minerals which are characteristic of acid-sulfate alteration: hydrated silica, sulfates, phyllosilicates, and Fe-oxides. Relic hydrothermal systems will play a key role in future investigations of Mars and the search for biosignatures. It is necessary to develop a detailed understanding of the mineral assemblages which form in these environment, and the geochemical processes by which they arise. This dissertation work addresses our ability to confidently and thoroughly characterize hydrothermal acid-sulfate mineral assemblages using rover-deployed instrumentation methods, and the role of high Fe parent basalts on secondary mineralogy.

Analysis of hydrothermal deposits was completed using Mars analog instrumentation to identify strengths and weaknesses for each method. VNIR, XRD, and Raman laser spectrometers analyzed 100 hydrothermally altered terrestrial samples. Results indicate phyllosilicates may be detected in XRD without any additional sample preparation when present at ≥ 10 wt %. VNIR was particularly useful for the identification of phyllosilicates and silica; however, these deposits are easily missed when observed with limited rover VNIR. For more robust phyllosilicate detection and “ground truthing” of orbital data, VNIR spectrometers on future rover payloads should cover the entire 300 – 2500 nm range.

Previous work has shown that parent rock composition plays a significant role in secondary mineral assemblage, and Icelandic basalts are among the closest terrestrial analogs for Mars. Our examination of the role of primary Fe content on secondary mineralogy found ~60 % Fe natroalunite forming in Iceland, adding to the growing list of natural systems containing intermediate alunite group minerals. There is a direct correlation between parent Fe and the abundance of Fe-bearing secondary minerals. Projected trends from our laboratory investigations indicate 20 – 32 wt % Fe-bearing mineralogy should form in Martian systems, similar to products from our terrestrial basalts. Alteration of crystalline “Mars” basalt produced both Fe-sulfates and Fe-oxides while all others contained only Fe-sulfates, indicating a transition to co-precipitation at > 17.0 wt % parent FeOT.

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