Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p53a1432w&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P53A-1432
Other
6094 Instruments And Techniques, 6225 Mars, 6969 Remote Sensing
Scientific paper
The majority of the equatorial regions of Mars are basaltic sands labeled Surface Type 1 (ST1). This MGS TES orbital thermal infrared (TIR) end-member is often compared to laboratory TIR data of Deccan Trap flood basalt from central India. Although subtle spectral differences exist (to be shown), the two likely have similar abundances and composition of labradorite and clinopyroxenes augite and pigeonite. This has been confirmed by recent works utilizing Mini-TES data of Meridiani sands and Gusev soils (both ST1) along with data from other MER instruments. Further, the TIR spectrum of Deccan basalt from Lonar Crater, India that was shocked 20-40 GPa is an exact match to the TIR spectrum of the Los Angeles shergottite in that both contain 45% maskelynite and 35% augite/pigeonite. This strengthens the comparison of ST1 to Deccan basalt and suggests that Los Angeles was ST1 bedrock before ejection. However, the TIR spectrum of ST1 and Deccan basalt both differ from the laboratory spectra of most basaltic shergottites, which contain more clinopyroxene than plagioclase. Further, the shergottites contain shattered clinopyroxenes and maskelynite, or plagioclase feldspar shock compressed to a diaplectic glass of plagioclase composition, that was created in the impact event that launched them from Mars. Presumably, the original basaltic bedrock from which shergottites originated contain the original plagioclase feldspar and unshattered clinopyroxenes. Whereas there exists evidence for olivine and orthopyroxene on Mars, large occurrences of these CPX-rich shergottites (not to be confused with pyroxenites or Nakhlites) have not been located using a laboratory TIR spectrum as an orbital end-member. However, one particular MER-B target named Bounce Rock has APXS and Mössbauer spectra similar to some shergottites such as Zagami. Mineral abundances resulting from the deconvolution of the Mini-TES spectrum of Bounce Rock, where the effects of dust have been removed, are similar to CPX-rich shergottites except that Bounce Rock appears to have spectral features attributed to plagioclase and not maskelynite. A comparison of the dust-removed Mini-TES spectrum of Bounce Rock to laboratory spectra of sherogottites Zagami and NWA 2986 share spectral features attributed to pigeonite and augite but the position of the Christiansen Feature (from comparisons to both experimentally shocked basalt and terrestrial shocked basalt) suggest that Bounce Rock is the unshocked version of these shergottites. This is significant because an unshocked shergottite will never be available in meteorite collections or traditional spectral libraries as all SNC's are shocked in their ejection event. Hence, the Mini-TES spectrum of Bounce Rock, while not from a bedrock exposure in Meridiani, is an excellent end-member to search for shergottite-like terrains on Mars. Spectral plots of the above comparisons between ST1, Deccan basalt, shocked Lonar basalt, Bounce Rock, and several shergottites will be shown along with early results of the orbital search for shergottite-like terrains.
Christensen Paul
Wright Steve
Wyatt Mark
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