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Published June 28, 2016 | Published + Supplemental Material
Journal Article Open

Silicic volcanism on Mars evidenced by tridymite in high-SiO₂ sedimentary rock at Gale crater


Tridymite, a low-pressure, high-temperature (>870 °C) SiO₂ polymorph, was detected in a drill sample of laminated mudstone (Buckskin) at Marias Pass in Gale crater, Mars, by the Chemistry and Mineralogy X-ray diffraction instrument onboard the Mars Science Laboratory rover Curiosity. The tridymitic mudstone has ∼40 wt.% crystalline and ∼60 wt.% X-ray amorphous material and a bulk composition with ∼74 wt.% SiO₂ (Alpha Particle X-Ray Spectrometer analysis). Plagioclase (∼17 wt.% of bulk sample), tridymite (∼14 wt.%), sanidine (∼3 wt.%), cation-deficient magnetite (∼3 wt.%), cristobalite (∼2 wt.%), and anhydrite (∼1 wt.%) are the mudstone crystalline minerals. Amorphous material is silica-rich (∼39 wt.% opal-A and/or high-SiO₂ glass and opal-CT), volatile-bearing (16 wt.% mixed cation sulfates, phosphates, and chlorides−perchlorates−chlorates), and has minor TiO₂ and Fe₂O₃T oxides (∼5 wt.%). Rietveld refinement yielded a monoclinic structural model for a well-crystalline tridymite, consistent with high formation temperatures. Terrestrial tridymite is commonly associated with silicic volcanism, and detritus from such volcanism in a "Lake Gale" catchment environment can account for Buckskin's tridymite, cristobalite, feldspar, and any residual high-SiO₂ glass. These cogenetic detrital phases are possibly sourced from the Gale crater wall/rim/central peak. Opaline silica could form during diagenesis from high-SiO₂ glass, as amorphous precipitated silica, or as a residue of acidic leaching in the sediment source region or at Marias Pass. The amorphous mixed-cation salts and oxides and possibly the crystalline magnetite (otherwise detrital) are primary precipitates and/or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions, temperatures, and acidities. Anhydrite is post lithification fracture/vein fill.

Additional Information

© 2016 National Academy of Sciences. Freely available online through the PNAS open access option. Contributed by John P. Grotzinger, May 5, 2016 (sent for review March 18, 2016); reviewed by Jon Blundy, Robert M. Hazen, and Harry Y. McSween) We acknowledge the unwavering support of the JPL engineering and MSL operations staff. This research was supported by the NASA Mars Science Laboratory Mission. The MSL APXS was financed and managed by the Canadian Space Agency, with MacDonald Dettwiler & Assoc., Brampton, as prime subcontractor for the construction of the instrument. Operation of the MSL APXS is supported by CSA Contract 9F052-110786 and by NASA. Some of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. J.D.F. thanks the Danish Villum Foundation for support. S.P.S. acknowledges UK Space Agency funding. Author contributions: R.V.M., D.T.V., D.F.B., R.G., S.J.C., D.W.M., S.M.M., A.S.Y., J.P.G., T.F.B., and J.-M.M. designed research; R.V.M., D.T.V., D.F.B., R.G., S.J.C., E.B.R., D.W.M., S.M.M., R.T.D., A.H.T., A.S.Y., J.P.G., C.N.A., T.F.B., J.A.C., D.J.D.M., J.D.F., K.V.F., J.F., T.G.G., and J.-M.M. performed research; R.V.M., D.T.V., D.F.B., R.G., S.J.C., E.B.R., D.W.M., S.M.M., R.T.D., A.H.T., A.S.Y., J.P.G., C.N.A., T.F.B., J.A.C., D.J.D.M., J.D.F., K.V.F., J.F., T.G.G., J.-M.M., E.M.S., and S.P.S. analyzed data; and R.V.M. and J.P.G. wrote the paper. Reviewers: J.B., Bristol University; R.M.H., Carnegie Institution of Washington; and H.Y.M., The University of Tennessee, Knoxville. The authors declare no conflict of interest. Data deposition: CheMin and APXS experiment data records and CheMin diffraction patterns have been deposited with the NASA Planetary Data System at pds-geosciences.wustl.edu/msl/msl-m-chemin-4-rdr-v1/mslcmn_1xxx/ for the CheMin data and pds-geosciences.wustl.edu/msl/msl-m-apxs-4_5-rdr-v1/mslapx_1xxx/ for the APXS data. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1607098113/-/DCSupplemental.

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Published - PNAS-2016-Morris-7071-6.pdf

Supplemental Material - pnas.1607098113.sapp.pdf


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