Manganese-Iron Phosphate Nodules at the Groken Site, Gale Crater, Mars

Creators: Treiman, Allan H.¹; Lanza, Nina L.²; VanBommel, Scott³; Berger, Jeff⁴; Wiens, Roger⁵; Bristow, Thomas⁶; Johnson, Jeffrey⁷; Rice, Melissa⁸; Hart, Reginald⁸; McAdam, Amy⁹; Gasda, Patrick²; Meslin, Pierre-Yves¹⁰; Yen, Albert¹¹; Williams, Amy J.¹²; Vasavada, Ashwin¹¹; Vaniman, David¹³; Tu, Valerie⁴; Thorpe, Michael⁹; Swanner, Elizabeth D.¹⁴; Seeger, Christina¹⁵; Schwenzer, Susanne P.¹⁶; Schröder, Susanne¹⁷; Rampe, Elizabeth⁴; Rapin, William¹⁸; Ralston, Silas J.⁴; Peretyazhko, Tanya⁴; Newsom, Horton¹⁹; Morris, Richard V.⁴; Ming, Douglas⁴; Loche, Matteo¹⁰; Le Mouélic, Stéphane²⁰; House, Christopher²¹; Hazen, Robert²²; Grotzinger, John P.¹⁵; Gellert, Ralf²³; Gasnault, Olivier⁸; Fischer, Woodward W.¹⁵; Essunfeld, Ari²; Downs, Robert T.²⁴; Downs, Gordon W.²⁴; Dehouck, Erwin²⁵; Crossey, Laura J.¹⁹; Cousin, Agnes¹⁰; Comellas, Jade M.²⁶; Clark, Joanna V.¹⁵; Clark, Benton²⁷; Chipera, Steve¹³; Caravaca, Gwenaël¹⁸; Bridges, John²⁸; Blake, David F.⁶; Anderson, Ryan²⁹

1. Lunar and Planetary Institute
2. Los Alamos National Laboratory
3. Washington University in St. Louis
4. Johnson Space Center
5. Purdue University West Lafayette
6. Ames Research Center
7. Johns Hopkins University Applied Physics Laboratory
8. Western Washington University
9. Goddard Space Flight Center
10. Observatoire Midi-Pyrénées
11. Jet Propulsion Lab
12. University of Florida
13. Planetary Science Institute
14. Iowa State University
15. California Institute of Technology
16. The Open University
17. Deutsche Zentrum für Luft- und Raumfahrt (DLR)
18. Research Institute in Astrophysics and Planetology
19. University of New Mexico
20. Laboratoire de Planétologie et Géodynamique de Nantes
21. Pennsylvania State University
22. Carnegie Institution for Science
23. University of Guelph
24. University of Arizona
25. Claude Bernard University Lyon 1
26. University of Hawaii at Manoa
27. Space Science Institute
28. University of Leicester
29. United States Geological Survey

Abstract

The MSL Curiosity rover investigated dark, Mn-P-enriched nodules in shallow lacustrine/fluvial sediments at the Groken site in Glen Torridon, Gale Crater, Mars. Applying all relevant information from the rover, the nodules are interpreted as pseudomorphs after original crystals of vivianite, (Fe²⁺,Mn²⁺)₃(PO₄)₂·8H₂O, that cemented the sediment soon after deposition. The nodules appear to have flat faces and linear boundaries and stand above the surrounding siltstone. ChemCam LIBS (laser-induced breakdown spectrometry) shows that the nodules have MnO abundances approximately twenty times those of the surrounding siltstone matrix, contain little CaO, and have SiO₂ and Al₂O₃ abundances similar to those of the siltstone. A deconvolution of APXS analyses of nodule-bearing targets, interpreted here as representing the nodules’ non-silicate components, shows high concentrations of MnO, P₂O₅, and FeO and a molar ratio P/Mn = 2. Visible to near-infrared reflectance of the nodules (by ChemCam passive and Mastcam multispectral) is dark and relatively flat, consistent with a mixture of host siltstone, hematite, and a dark spectrally bland material (like pyrolusite, MnO₂). A drill sample at the site is shown to contain minimal nodule material, implying that analyses by the CheMin and SAM instruments do not constrain the nodules’ mineralogy or composition. The fact that the nodules contain P and Mn in a small molar integer ratio, P/Mn = 2, suggests that the nodules contained a stoichiometric Mn-phosphate mineral, in which Fe did (i.e., could) not substitute for Mn. The most likely such minerals are laueite and strunzite, Mn²⁺Fe³⁺₂(PO₄)₂(OH)₂·8H₂O and –6H₂O, respectively, which occur on Earth as alteration products of other Mn-bearing phosphates including vivianite. Vivianite is a common primary and diagenetic precipitate from low-oxygen, P-enriched waters. Calculated phase equilibria show Mn-bearing vivianite could be replaced by laueite or strunzite and then by hematite plus pyrolusite as the system became more oxidizing and acidic. These data suggest that the nodules originated as vivianite, forming as euhedral crystals in the sediment, enclosing sediment grains as they grew. After formation, the nodules were oxidized—first to laueite/strunzite yielding the diagnostic P/Mn ratio, and then to hematite plus an undefined Mn oxy-hydroxide (like pyrolusite). The limited occurrence of these Mn-Fe-P nodules, both in space and time (i.e., stratigraphic position), suggests a local control on their origin. By terrestrial analogies, it is possible that the nodules precipitated near a spring or seep of Mn-rich water, generated during alteration of olivine in the underlying sediments.

Copyright and License

© 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Acknowledgement

The authors acknowledge the support they received, and have received, from NASA’s Mars Exploration Program through the Mars Science Laboratory project, and their respective instrument PIs and the MSL participating scientist program (J.R. Johnson, 80NSSC22K0779). Part 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 (NASA). Treiman is grateful for contract support through the CheMin instrument. The Lunar and Planetary Institute (LPI) is operated by Universities Space Research Association (USRA) under a cooperative agreement with the Science Mission Directorate of NASA. We are grateful for corrections and comments from two anonymous reviewers. LPI Contribution No. 3000.

Funding

Funding for this work came from NASA’s Mars Exploration Program through the Mars Science Laboratory project, via their respective instrument PIs and the MSL Participating Scientist Program.

Contributions

Conceptualization, A.H.T. and N.L.L.; Methodology, all authors; Investigation, all authors; Resources, all authors; Data Curation, all authors; Writing—Original Draft Preparation, A.H.T.; Writing—Review and Editing, A.H.T.; Visualization, G.C.; Supervision, T.B.; Project Administration, A.V.; Funding Acquisition, A.V. All authors have read and agreed to the published version of the manuscript.

Data Availability

All data reported here are available through the NASA Planetary Data System (PDS). ChemCam relative reflectance spectra can be found here: https://pds-geosciences.wustl.edu/msl/urn-nasa-pds-msl_chemcam_psv_calibrated/. CheMin data are also available at https://odr.io/chemin (all accessed 7 July 2023).

Supplemental Material

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/min13091122/s1, 1. Text File: a. Chronology of events at and near Mozie_Law; b. Documentation of Mastcam multispectral observations; c. Additional LIBS data; d. X-ray diffraction data on amorphous phosphate material; e. Description of thermochemical data and calculations f. Morphology of vivianite crystals, compared to those of the Groken nodules. 2. ThermoddemV1.10_Groken_june2023.tdat file for Geochemist’s Workbench (GWB). 3. Spreadsheet [GrokenSupp3ThermoCalcData.xlsx] documenting calculations to estimate DG_f and K_sp for Mn-Fe-P phases.

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