Widespread Weathered Glass on the Surface of Mars

نویسندگان

  • Briony Horgan
  • James F. Bell
چکیده

Low albedo sediments cover >107 km2 in the northern lowlands of Mars, but the composition and origin of these widespread deposits have remained ambiguous despite many previous investigations. Here we use near-infrared spectra acquired by the Mars Express OMEGA (Observatoire pour la Minéralogie, l’Eau, les Glaces, et l’Activité) imaging spectrometer to show that these sediments exhibit spectral characteristics that are consistent with both high abundances of iron-bearing glass and silica-enriched leached rinds on glass. This interpretation is supported by observations of low-albedo soil grains with possible rinds at the Phoenix Mars Lander landing site in the northern lowlands. By comparison with the extensive glass-rich dune fi elds and sand sheets of Iceland, we propose an explosive volcanic origin for these glass-rich sediments. We also propose that the glassy remnant rinds on the sediments are the result of postdepositional alteration, as these rinds are commonly formed in arid terrestrial volcanic environments during water-limited, moderately acidic leaching. These weathered, glass-rich deposits in the northern lowlands are also colocated with the strongest concentrations of a major global compositional surface type previously identifi ed in mid-infrared spectra, suggesting that they may be representative of global processes. Our results provide potential confi rmation of models suggesting that explosive volcanism has been widespread on Mars, and also raise the possibilities that glass-rich volcaniclastics are a major source of eolian sand on Mars and that widespread surfi cial aqueous alteration has occurred under Amazonian climatic conditions. Figure 1. OMEGA (Observatoire pour la Minéralogie, l’Eau, les Glaces, et l’Activité) near-infrared spectra of Mars northern lowlands that are consistent with iron-bearing glass, compared with north polar average regional dust (red) and spectrum consistent with pyroxene (orange). Points indicate unsmoothed spectra. A: Spectra showing concavity variations, scaled to 1.0 at 0.7 μm and offset for clarity. Vertical lines indicate wavelengths used to calculate concavity. B: Spectra from A ratioed with average regional dust spectra, compared to leached glass rinds. Black—glassy basaltic sand after 83 days exposure to oxidizing, acidic solution (pH 1) (Horgan et al., 2011); gray—MIO and MUO black coatings of Minitti et al. (2007). Continua are indicated by bounding curves. C: Spectra from B after continuum removal, compared to laboratory spectra of mafi c phases. Vertical lines indicate typical range of 1 μm band centers for glass. as doi:10.1130/G32755.1 Geology, published online on 26 March 2012

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تاریخ انتشار 2012