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Data from: Brine driven destruction of clay minerals in Gale crater, Mars

Citation

Bristow, Thomas (2021), Data from: Brine driven destruction of clay minerals in Gale crater, Mars, Dryad, Dataset, https://doi.org/10.5061/dryad.k3j9kd576

Abstract

This repository contains files and non-commercial software associated with the journal article "Brine Driven Destruction of Clay Minerals in Gale Crater, Mars.

The article presents mineralogical, geochemical, and sedimentological observations made by the Mars Science Laboratory rover Curiosity in an area called Glen Torridon, Gale crater, Mars. Rocks exposed in Glen Torridon were deposited in a lake that occupied the floor of Gale crater about 3.5 billion years ago and are stratigraphic and depositional equivalents of rocks exposed ~ 400m away on Vera Rubin ridge. The mineralogy of rocks in these two areas are different despite forming in the same lake at the same time. Glen Torridon rocks contain about 30 wt % clay minerals and 2 wt % or less of the mineral hematite (an iron oxide). In contrast, Vera Rubin ridge rocks contain 5 to 13 wt % clay minerals, with larger quantities (between 9 and 16 wt %) of iron oxide and oxyhydroxide minerals. The observed differences in mineralogy are attributed to preferential post-depositional alteration of Vera Rubin ridge rocks by silica-poor brines. These brines are thought to have formed during the deposition of sedimentary strata of the 'sulfate-bearing unit' that overlie Glen Torridon and Vera Rubin ridge rocks. Orbital spacecraft have detected magnesium sulfates in the sulfate-bearing unit. The presence of these highly soluable salts imply that changing climate and/or hydrological conditions in Gale crater resulted in the formation of dense brines during deposition of the sulfate-bearing unit. It is hypothesized that brines infiltrated older clay-bearing sediments, converting iron-rich clay minerals to iron oxides and oxyhydroxides. Glen Torridon rocks also contain a mineral phase not previously identified on the mission. This mineral gives rise to a distinctive x-ray diffraction peak represents a interplanar spacing of 9.22 angstroms. This phase is identified as a mixed-layer serpentine-talc and is thought to have been transported into the crater floor by rivers.

This repository contains:

- Files needed to perform mineral search and Rietveld refinement of measured x-ray diffraction data using BGMN and MDI Jade software. 

- A non-commerical Excel-based program called FULLPAT, used for mineral and x-ray amorphous quantification of x-ray diffraction patterns collected by the CheMin instrument aboard Curiosity.

Python code that was used to identify the 9.22 angstrom phase through automated search the American Mineralogist Crystal Structure Database.

- Collection times of Alpha Particle X-ray Spectrometer analyses of bulk rock geochemical presented in the article that can be used to retrieve raw data from NASA's Planetary Data system (https://pds-geosciences.wustl.edu/msl/msl-m-apxs-4_5-rdr-v1/mslapx_1xxx/extras/)

- A compilation of Li abundances across Vera Rubin ridge and Glen Torridon measured by the ChemCam that were presented in the article and used as a proxy for rock clay mineral content.

Methods

Details of how this dataset was collected can be found in Supplementary Materials published with the journal article.

Usage Notes

The file "APXS_data_Fig.S5_Table_S1.xlxs" is a list of the analysis start times for Alpha Particle X-ray spectrometer data shown in Fig. S5 and Table S1 of the article. Data can be retrieved from: https://pds-geosciences.wustl.edu/msl/msl-m-apxs-4_5-rdr-v1/mslapx_1xxx/extras/

The file "ChemCam_Li_Fig.2.xlsx" is a compiled list of the sol, spacecraft clock identification, and Li abundance of each ChemCam observation point shown in Fig. 2 of the article. All ChemCam spectra utilized to calculate Li abundances in this file can be acquired from: https://pds-geosciences.wustl.edu/msl/msl-m-chemcam-libs-4_5-rdr-v1/mslccm_1xxx/data/

The "FULLPAT" zip folder contains a modified version of the Excel based program FULLPAT used to analyze CheMin instrument XRD data. The folder also contains a copy of the FULLPAT user manual. 

The "BGMN files" and "Jade files" zip folders contain: the crystal structure files, measured XRD patterns from the CheMin instrument, and measured XRD patterns of standards used to analyze Mars XRD patterns using BGMN and MDI Jade software.

The "Kilmarie-9.22-A-peak-search-master" zip folder contains python code used to search for candidate phases that can account for a peak at 9.22 angstroms observed in the Kilmarie sample. 

Funding

National Aeronautics and Space Administration