Mathematics – Logic
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p11e..03m&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P11E-03
Mathematics
Logic
5410 Composition (1060, 3672), 5464 Remote Sensing, 6225 Mars
Scientific paper
The OMEGA investigation on the Mars Express spacecraft identified phyllosilicates across a range of martian geologic terrains, but importantly the mineral occurrences were largely confined to Noachian-aged terrains. This led to the new paradigm that that an active hydrologic system was restricted to early Mars history. The order of magnitude increase in spatial resolution of the CRISM instrument on Mars Reconnaissance Orbiter over OMEGA is used here to assess mineralogic diversity and stratigraphic relationships in several phyllosilicate regions. CRISM data show definitive evidence for diagnostic Al-OH and Fe/Mg-OH absorptions of phyllosilicate minerals, similar to those seen by OMEGA, but reveal mineralogic diversity down to the fine spatial resolution of the instrument. Al-OH phyllosilicates have been confirmed in Mawrth Vallis and are identified for the first time in the Nili Fossae region, displaying spectra consistent with kaolinite, illite and/or muscovite. A diversity of Fe/Mg-OH phyllosilicates is observed; smectites such as nontronite and saponite are the most common, but chlorites are also present in some locations. A new spectral class of mineral is found interpreted to be hydrated volcanic or impact glass. This material is found in isolated regions in the Noachian highlands. Fe/Mg phyllosilicate and hydrated glasses are found in rims, ejecta, and central peaks of craters in the southern highland Noachian cratered terrain indicating excavation of altered crust from depth. Phyllosilicate is also found in deposits clearly laid by water in Jezero, Ritchy, and Holden crater. Stratigraphic relationships in the many regions show unaltered volcanic or igneous lithologies overlying phyllosilicate-bearing rocks indicating an abrupt cessation of widespread alteration in the late Noachian. The predominance of smectite clay signatures implies moderate to low temperatures of formation (<200°C) such as might have existed in the near surface or shallow crust. The formation of phyllosilicate and hydrated glass could have been a consequence of near surface weathering or low temperature hydrothermal processes in a cooling crust
Arvidson Ray E.
Bibring J.
Bishop Janice L.
Clark Rebecca
Ehlmann Bethany L.
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