Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p13a1256m&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P13A-1256
Mathematics
Logic
[5415] Planetary Sciences: Solid Surface Planets / Erosion And Weathering, [5462] Planetary Sciences: Solid Surface Planets / Polar Regions, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The North Polar Cap of Mars is an accumulation of ice layers with various amounts of interstratified dust particles. A dune field surrounds this polar cap. On one of the densest part of this dune field, Olympia Undae, Langevin et al. (Science, 2005) have detected calcium-rich sulfates (gypsum). To constrain the origin of these gypsum deposits, we performed an integrated morphological, structural and compositional analyses of a key area where it is possible to see the circum-polar dune field, the surface of the ice cap and a cross-section through the ice cap. The mineralogical composition of this area is investigated by applying a spectral derivative method to data acquired by OMEGA and CRISM hyperspectral imaging spectrometers. These are compared to laboratory spectra of ice-gypsum mixtures in simulated martian pressure and temperature conditions. We find that dunes of the circumpolar field and dust interstratified in the ice cap have the same composition. Both contain gypsum. Landforms produced by sublimation of ice are also visible on dust-rich layers of the ice cap. We therefore infer that the superficial circumpolar dust deposits correspond to a sublimation till produced by the ice cap. Circumpolar gypsum-rich deposits thus derive directly from the ice cap. Gypsum crystals are released at the surface of the cap as the ice sublimes. This material is then reworked by winds and forms the circumpolar dunes. There are two hypotheses for the ultimate origin of the gypsum crystals. (1) Pre-existing gypsum crystals might have been deposited together with ice crystals during the formation of the ice cap. (2) Authigenic gypsum crystals might have grown within the ice cap by weathering of dust trapped in the ice. The second hypothesis is consistent with the existence of authigenic sulfate inclusions in terrestrial polar ice (Ohno et al., GRL, 2006) and with the formation process suggested by Niles et al. (Nature, 2009) for martian equatorial sulfates.
Bourgeois Olivier
Le Deit Laetitia
Le Mouélic Stéphane
Massé Marion
Verpoorter C.
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