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Wishstone to Watchtower; amorphous alteration of plagioclase-rich rocks in Gusev Crater, Mars

Steven W. Ruff and Victoria E. Hamilton
Wishstone to Watchtower; amorphous alteration of plagioclase-rich rocks in Gusev Crater, Mars
American Mineralogist (February 2017) 102 (2): 235-251


Previous observations by the Spirit rover in Gusev crater revealed a suite of rocks dubbed Wishstone and Watchtower Class in which the parent lithology and daughter products of a distinctive style of aqueous alteration are evident. Results from Spirit's Miniature Thermal Emission Spectrometer (Mini-TES; approximately 2000-340 cm (super -1) ) were compromised by dust contamination of one of the instrument's mirrors, for which a correction has since been developed. Now we have documented nearly 200 examples of rocks encompassing the span of alteration from Wishstone Class, which spectrally resemble minimally altered plagioclase-phyric basalt, to the most altered Watchtower Class. Among them is a rock dubbed Bruce that may be a previously unrecognized alteration spectral end-member. We employed factor analysis/target transformation and linear least-squares modeling to investigate the spectral characteristics and mineralogy of these rocks. Our results amplify those of a prior preliminary analysis showing that alteration produced a material resembling basaltic glass that masks the spectral features of plagioclase. The association of this amorphous silicate component with a ferric iron nanophase oxide phase identified via Spirit's Mossbauer spectrometer is now clearly shown by our data, further characterizing the distinctive mineralogic expression of the alteration. These components and the absence of any recognizable secondary silicates or opaline silica may be an expression of alteration in the extreme aridity and cold of the martian environment. Similar mineralogic characteristics of soil measured with the CheMin X-ray diffraction instrument on the Curiosity rover in Gale crater may be an indication that this alteration process is widespread on Mars.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 102
Serial Issue: 2
Title: Wishstone to Watchtower; amorphous alteration of plagioclase-rich rocks in Gusev Crater, Mars
Affiliation: Arizona State University, School of Earth and Space Exploration, Tempe, AZ, United States
Pages: 235-251
Published: 201702
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 56
Accession Number: 2017-018515
Categories: Extraterrestrial geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 8 tables
Secondary Affiliation: Southwest Research Institute, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201713
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