Hematite-rich regions on Mars

Post by Cathy Weitz and Melissa Lane Planetary Science Institute, Tucson, Arizona, USA.

Fine-grained red hematite is a common mineral on the surface of Mars and explains much of the reddish color for martian soils and rocks. However, hematite can also be gray in color if it is coarser grained. Gray, crystalline hematite has been identified by the Thermal Emission Spectrometer (TES) at several sites on Mars , including: Meridiani Planum, Aram Chaos, Valles Marineris, Aureum Chaos, and Iani Chaos (Image 1) [Christensen et al., 2000; 2001; Glotch and Christensen, 2005; Glotch and Rogers, 2007; Noe Dobrea et al., 2007; Weitz et al., 2007]. At Meridiani, Aram Chaos, Iani Chaos, and Aureum Chaos the hematite units are confined to a specific layer or fairly continuous unit [e.g., Christensen et al., 2001, Glotch and Christensen, 2005]. Whereas,  in Valles Marineris the gray hematite is more patchy in distribution and scattered in separate troughs [Weitz et al., 2007; Le Deit et al., 2008].

August 2010

Image 1: Three locations where TES has detected gray hematite. The colors represent non-absolute estimated abundances, with red indicating highest abundances and blues lower amounts. (a) Central Valles Marineris. (b) Aram Chaos. (c) Meridiani Planum, where the location of the Mars Exploration Rover Opportunity landing site is shown by a black cross.

Several origins for the gray hematite were proposed by Christensen et al. [2000a; 2001]. Their favored interpretations were 1) the direct precipitation of fine-grained hematite from Fe-rich circulating fluids of hydrothermal origin. Or 2) a low-temperature precipitation of fine-grained Fe-oxides/hydroxides from standing, oxygenated, Fe-rich water, followed by subsequent alteration (coarsening) to gray hematite.

August 2010

Image 2: Example of terrain with high hematite abundances in Candor Chasma. Hematite occurs throughout this image in association with dark debris and slightly brighter rippled terrain. The black box indicates the location of the blowup of HiRISE image PSP_002142_1730 shown in (b). (b) Blowup showing outcrops of Light-Toned Rocks (LTR) that are partially buried beneath the dark debris unit. Edges along the dark debris unit (bold arrows) are sharp and appear to have topographic expression, consistent with a competent unit.

It was the detection of gray hematite in Meridiani Planum that led scientists to select this location as the landing site for one of the Mars Exploration Rovers (MER). The rover Opportunity landed in Meridiani Planum on January 24, 2004. After driving on the surface for several sols, instruments on the rover allowed scientists to determine that millimeter-size spherules (informally termed ‘blueberries’ by the MER science team) contained the gray hematite [Christensen et al., 2004; Squyres et al., 2004]. The hematite-rich spherules are postulated to have formed by secondary alteration of the sulfate-rich outcrop as water permeated through the rocks and produced concretions [McLennan et al., 2005]. Hematite-cemented concretions formed by groundwater flow have been found on Earth in the Jurassic Navajo Sandstone of southern Utah [Chan et al., 2004], although they are dominated by quartz.

August 2010

Image 3: (a) Opportunity Navcam Sol 359 image illustrating the surface morphology along the plains of Meridiani Planum. Rover tracks can be seen in the soils. (b) Microscopic Imager image merged with Pancam false-color of the typical grains that compose the soils seen along the plains at the Meridiani Planum landing site. The larger grains average 1.6 mm in diameter and most are the hematite-rich spherules (blue color) that form a lag on the surface. The finer grains that are <100 mm in size are dust and basaltic sand.

The size of the spherules ranges from about 1-4.5 mm [Weitz et al., 2006; Calvin et al., 2008]. In bedrock outcrops, the spherules make up only a few volume percent of the rocks so their signature is not strong enough to be detected in the rocks themselves from orbit. It is only because erosion of the sulfate-rich host rock has concentrated the more resistant hematite spherules in larger abundances as a lag deposit in the soils that the signature at Meridiani Planum was strong enough to be detected from orbit. Hence, other sulfate-rich rocks with hematite spherules may exist on Mars, but the hematite may not be concentrated at high enough abundances on the surface to be detected from orbit.

Further Reading

Calvin, W. M., et al. (2008), Hematite spherules at Meridiani: Results from MI, Mini-TES, and Pancam, J. Geophys. Res., 113, E12S37, doi:10.1029/2007JE003048.

Chan, M. A., Beitler, B., Parry, W. T., J., O., and Komatsu, G. (2004). A possible terrestrial analogue for haematite concretions on Mars. Nature429, 731-734.

Christensen, P. R., J. L. Bandfield, R. N. Clark, K. S. Edgett, V. E. Hamilton, T. Hoefen, H. H. Kieffer, R. O. Kuzmin, M. D. Lane, M. C. Malin, R. V. Morris, J. C. Pearl, R. Pearson, T. L. Roush, S. W. Ruff, and M. D. Smith (2000) Detection of crystalline hematite mineralization on Mars by the Thermal Emission Spectrometer:  Evidence for near-surface water, J. Geophys. Res., 105, 9623-9642.

Christensen, P. R., R. V. Morris, M. D. Lane, J. L. Bandfield, and M. C. Malin, (2001) Global mapping of Martian hematite mineral deposits:  Remnants of water-driven processes on early Mars, J. Geophys. Res., 106, 23873-23885.

Christensen, P. R., et al. (2004), Mineralogy at Meridiani Planum from the Mini-TES experiment on the Opportunity Rover, Science, 306, 1733–1739.

Glotch, T. D., and P. R. Christensen (2005), Geologic and mineralogic mapping of Aram Chaos: Evidence for a water-rich history, J. Geophys. Res., 110, E09006, doi:10.1029/2004JE002389.

Glotch, T. D., and A. D. Rogers (2007), Evidence for aqueous deposition of hematite- and sulfate-rich light-toned layered deposits in Aureum and Iani Chaos, Mars, J. Geophys. Res., 112, E06001, doi:10.1029/2006JE002863.

Le Deit, L., S. Le Mouelic, O. Bourgeois, J.-P. Combe, D. Mege, C. Sotin, A. Gendrin, E. Hauber, N. Mangold, and J.-P. Bibring (2008), Ferric oxides in East Candor Chasma, Valles Marineris (Mars) inferred from analysis of OMEGA/Mars Express data: Identification and geological interpretation, J. Geophys. Res., 113, E07001, doi:10.1029/2007JE002950.

McLennan, S. M., et al. (2005), Provenance and diagenesis of the evaporite-bearing Burns formation, Meridiani Planum, Mars, Earth Planet. Sci. Lett., 240(1), 95– 121.

Noe Dobrea E, F. Poulet, and M.C. Malin (2008) Correlations between hematite and sulfates in the chaotic terrain east of Valles Marineris, Icarus, 193, 516-534.

Squyres, S. W., et al. (2004), In situ evidence for an ancient aqueous environment at Meridiani Planum, Mars, Science, 306, 1709– 1714

Weitz, C. M., R. C. Anderson, J. F. Bell III, W. H. Farrand, K. E. Herkenhoff, J. R. Johnson, B. L. Jolliff, R. V. Morris, S. W. Squyres, and R. J. Sullivan (2006), Soil grain analyses at Meridiani Planum, Mars, J. Geophys. Res., 111, E12S04, doi:10.1029/2005JE002541.

Weitz, C. M., M. D. Lane, M. Staid, and E. N. Dobrea (2008), Gray hematite distribution and formation in Ophir and Candor chasmata, J. Geophys. Res., 113, E02016, doi:10.1029/2007JE002930.

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