Early Archean alteration minerals in mafic-ultramafic rocks of the Barberton greenstonebelt as petrological analogs for clay mineralogy on Mars

1Eugene G. Grosch,2Janice L. Bishop,3Christian Mielke,4Alessandro Maturilli,4Jörn Helbert
American Mineralogist 106, 672–684 Link to Article [http://www.minsocam.org/MSA/AmMin/TOC/2021/Abstracts/AM106P0672.pdf]
1Geology Department, Rhodes University, Grahamstown/Makhanda 6140, South Africa 2
2Carl Sagan Center, SETI Institute and NASA-Ames Research Center, Mountain View, California 94043, U.S.A. 3
3GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam 4
4Institute for Planetary Research, DLR, Rutherfordstrasse 2, 12489, Berlin-Adlershof, Germany
Copyright: The Mineralogical Society of America

Characterization of terrestrial analog sites is critical for detection and determination of clay mineralogy in remote sensing studies of Mars aimed at geological, hydrological, and potentially biological
investigations. In this study, we investigate a suite of hydrothermally altered early Archean rocks from
the Barberton greenstone belt (BGB) of South Africa as potential petrological, mineralogical, and
spectral analogs to hydrothermally altered metabasalts and mafic-ultramafic intrusions in the martian
subsurface and impact craters. We present the first spectral imaging measurements on exceptionally
well-preserved early Archean mafic-ultramafic rocks from the BGB, with the aim of studying their
clay mineralogy and spectral signatures. Multiple spectral analyses were conducted on different
sample textures (rock powders, crushed rocks, and rock slabs) appropriate for Mars rover and remote
sensing exploration. Visible/near-infrared (VNIR) and mid-IR reflectance spectra were acquired on
particulate samples, while VNIR spectral imaging data were collected on rock slabs. Mid-IR emission
spectra were measured for the rock slabs and grains. Spectral features are compared from these different spectral techniques to identify the minerals present in the samples and compare macroscale vs.
microscale detections. The measured spectra reveal absorption bands that correspond to clay mineralogy of the serpentine and chlorite mineral groups, consistent with petrographic observations, as well
as magnetite, olivine, quartz, feldspar, and Al-phyllosilicate. The spectral data acquired in this study
expand the reference spectra data set for remote sensing studies. The implications of this study are that
rocks from early Archean greenstone belts, such as those of the BGB, serve as potential clay-bearing
petrological analogs for hydrothermal environments on Mars.

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