Ninth International Conference on Mars 2019 (LPI Contrib. No. 2089) 6251.pdf

INTERPRETING POTENTIALLY HABITABLE PAST CONDITIONS RECORDED IN ON MARS. E.M. Hausrath, UNLV, Las Vegas, NV 89154 [email protected]

Introduction: assemblages present on Jezero crater: Jezero crater, the future landing site Mars provide an important record of past aqueous con- of the Mars 2020 Rover, contains , Mg-rich car- ditions on that planet. Different mineral phases dis- bonates, Fe/Mg-smectite, siderite, and kaolinite [9-11]. solve at different rates depending on the pH, tempera- Some of these mineral phases may be detrital, trans- ture, and salinity of aqueous solutions, and weathered ported from the surrounding watershed [9]. Therefore, minerals can therefore record evidence of these condi- an examination of the mineral assemblages present in tions in the rock record. Similarly, secondary minerals Jezero crater sediments compared to parent material can provide evidence of the aqueous, and potentially may help constrain past aqueous conditions in Jezero habitable, conditions under which they formed. Exam- crater (Figure 1).

ining assemblages of primary and secondary minerals -6 ) 10 is therefore critical to assessing past aqueous and po- -1 siderite s -7 tentially habitable conditions on Mars. Here mineral -2 10 fayalite smectite -8 assemblages at three different locations on Mars are 10 kaolinite

examined using geochemical kinetics and thermody- 10-9 namics to assess the information they can provide on -10 past aqueous and potentially habitable conditions. 10 Gale crater: At Gale crater, Mars, abundant evi- 10-11

dence exists for past water-rock interactions [e.g. 1]. 10-12 However, multiple questions remain about the charac- 10-13 teristics of past water. Reactive transport modeling, Dissolution rate (mol mineral m mineral (mol rate Dissolution -14 which includes geochemical kinetics and thermody- 10 namics; transport, including advection, diffusion, and 10-15 dispersion; and reaction-induced porosity and permea- 2 4 6 8 10 pH bility feedback can be used to constrain these past Figure 1. Comparison of laboratory-measured dis- aqueous environments [2]. solution rates of magnesite, siderite, forsterite, fayal- Comparison of the Stimson formation sandstone at ite, kaolinite, and Fe/Mg smectite, phases observed at Gale crater with modern eolian deposits Rocknest and Jezero crater [9, 10], indicate that dissolution rates of Gobabeb suggest that dissolution of olivine and for- carbonate and olivine are predicted to be faster than mation of occurred due to the early cement- dissolution rates of smectite and kaolinite. In addition, ing fluids that flowed through the Stimson formation except at pH values of ~5, carbonate is predicted to [3, 4]. Examination of altered zones through dissolve more rapidly than olivine of a similar Fe and the Stimson formation compared to the bulk Stimson Mg composition (i.e. dissolution rates of siderite > formation indicate that dissolution of plagioclase, mag- fayalite, and magnesite > forsterite). Examination of netite, and , and precipitation of amorphous olivine and carbonate in detrital sediments compared silica and calcium sulfate occurred due to fluids that to parent material may therefore help constrain past flowed through the fractures [3, 4]. Reactive transport aqueous conditions, including pH, in Jezero crater. modeling of these water-rock interactions constrain at Similarly, different dissolution rates of clay minerals least two different aqueous solutions, the first near neu- may help interpret transitions in clay mineralogy ob- tral in pH, and the second very low in pH with high served at the landing site for the ExoMars Rover, Oxia sulfate concentrations, containing Ca, P, and Si [5]. Planum[12, 13]. Dissolution rate laws from [14] for Reactive transport modeling of potential scenarios magnesite, [15] for siderite, [16] (based on data for water-rock interactions in the Murray formation at compiled in [17]) for forsterite and kaolinite), smectite Gale crater [6, 7] tests the pH, temperature, and oxida- rate law from [18] based on data from [19] and [20], tion state of past aqueous conditions. Results of ongo- and fayalite assumed to dissolve 10x more rapidly than ing modeling [8] are most consistent with acidic condi- forsterite based on [21]. tions, low temperature or a combined low temperature Because forsterite, fayalite, magnesite, and siderite and high temperature scenario, and oxidizing fluids dissolve more rapidly than Fe/Mg and Al-bearing clay beneath the surface. Modeling water-rock interactions minerals (Figure 1), aqueously altered mixtures of oli- such as in these examples in the Stimson and Murray vine, carbonate, and clay minerals are predicted to be formations can help provide constraints on the types of depleted in olivine and carbonate relative to the parent potentially habitable past conditions on Mars. Ninth International Conference on Mars 2019 (LPI Contrib. No. 2089) 6251.pdf

material. Because carbonate dissolves more rapidly in and future returned samples can help place constraints laboratory experiments than olivine of the same com- on the characteristics of past aqueous environments on position except at ~ pH = 5, relative amounts of car- Mars. Information about the pH, temperature, salinity bonate and olivine in aqueously altered sediments ver- and other characteristics of past aqueous environments sus parent material may also help constrain the pH of can help inform our understanding of habitability and the interacting fluid. Examination of these mineral as- the search for potential past signs of life. semblages has the potential to help elucidate past smectite aqueous and potentially habitable conditions. 0 kaolinite Laboratory-measured precipitation rates of Mars-

relevant carbonate phases predict that hydromagnesite 50 would precipitate much more rapidly than magnesite at low temperatures (Figure 2; [22, 14]). Both magnesite [9] and hydromagnesite [11] are present at Jezero 100

crater. With detailed information on the geological (cm) Depth

context of the occurrence of these minerals from the 150 Mars 2020 Rover, the rates of their formation and dis- solution may help constrain past aqueous conditions in this environment. 200

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 calcite (Jimenez-Lopez et al., 2001) calcite (Romanek et al., 1992) moles clay mineral 10 siderite (Jimenez-Lopez and Romanek, 2004) magnesite (Saldi et al., 2009) Figure 3. Transition from Fe/Mg-bearing smectite to 8 rhodochrosite (Sternbeck, 1997) kaolinite in the top 2 m of soil on Earth. Moles of clay hydromagnesite (Gautier et al., 2015) 6 minerals calculated based on chemical and mineralog-

)

-1 4

hr ical data from [28]. Fe/Mg phyllosilicates and Al- -2 2 bearing clay minerals have been detected at Oxia

molm 0

 Planum [12, 13], and similar such transitions may -2 help interpret past water-rock interactions and poten- -4 tial habitability in that environment. log rate ( rate log -17.0 -17.2 -17.4 -17.6 References: -17.8 1. Grotzinger, et al., (2014) Sci., 343 1242777. 2. Steefel, et -18.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 al., (2015) CG., 19 445-478. 3. Yen, et al., (2017) EPSL, 471 Log () 186-198. 4. Frydenvang, et al., (2017) GRL, 44 4716–4724, Figure 2. Precipitation rates of calcite [23, 24], si- doi: 10.1002/2017GL073323. 5.Hausrath, et al., (2018) derite [25], magnesite [14], rhodochrosite [26], and EPSL, 491 1-10. 6. Rampe, et al., (2017) EPSL, 471 172- 185. 7. Hurowitz, et al., (2017) Sci., 356 eaah6849. 8. hydromagnestite [22] as a function of saturation state, Hausrath, et al. (2019) LPSC Abs #2050. 9. Goudge, et al., figure after [27]. (2015) JGR, 120 775-808. 10. Zastrow et al. (2019) LPSC Oxia Planum: Mineral assemblages, including Abs #2037. 11. Garczynski, et al. (2019) LPSC. Abs #2028. Fe/Mg-phyllosilicates [12] and Al-bearing clay miner- 12. Quantin et al. (2018) LPSC Abs #2863. 13. Quantin et als present on top of the Fe/Mg-bearing material in al., (2018) 5th ExoMars 2020 landing site workshop. 14. some areas [13], may also help shed light on past Saldi et al., (2009) GCA, 73 5646-5657. 15. Duckworth and aqueous and potentially habitable conditions at the Martin, (2004) AM, 89 554-563. 16. Bandstra and Brantley in Kinetics of Water-Rock Interaction, 2008. Springer: New future landing site of the ExoMars Rover, Oxia York.p. 211-257.17. Bandstra, J.Z., et al., in Kinetics of Planum. In weathering profiles on Earth, Fe/Mg- Water-Rock Interaction 2008, Springer: New York. p. 737- bearing smectites have been observed to transform to 823. 18. Gainey et al., (in rev) JGR 19. Gainey, et al., (2014) the Al-bearing clay mineral kaolinite in the top 2 m of GCA, 126 192-211.20. Palandri and Kharaka, 2004, USGS soil formed from weathered parent material of basaltic OFR 2004-1068.21. Wogelius and Walther, (1992) CG, 97 composition (e.g. Figure 3; [28]). Examination of 2 m 101-112. 22. Gautier, et al., (2014) GCA, 138 1-20. 23. deep soil profiles at Oxia Planum may similarly reveal Jiménez-López, et al., (2001) GCA, 65 3219-3231. 24. characteristic mineral transitions, shedding light on Romanek et al., (1992) GCA, 56 419-430. 25. Jimenez- Lopez and Romanek, (2004) GCA, 68 557-571. 26. past water-rock interactions and potential habitability. Sternbeck , (1997) GCA, 61 785-793. 27. Hausrath and Conclusions: Examination of mineral assemblages Olsen, (2013) AM, 98 897-906. 28. Hausrath, et al., (2011) from orbital and rover measurements, depth profiles, CG, 290 89-100.