Paper No. 10
Presentation Time: 4:00 PM
MINERALOGY OF MAWTH VALLIS, MARS, AS DETERMINED THROUGH ANALYSES OF CRISM IMAGES
BISHOP, Janice L.1, SAPER, Lee M.
2, MCKEOWN, Nancy K.
3, PARENTE, Mario
2, POULET, Francois
4 and MUSTARD, John F.
5, (1)Carl Sagan Center, SETI Institute and NASA-ARC, Mountain View, CA 94043, (2)Geological Sciences, Brown University, Box 1846, Providence, RI 02912, (3)Grant MacEwan University, 10700-104 Avenue, Edmonton, AB T5J 4S2, Canada, (4)Institut d' Astrophysique Spatiale (IAS), Orsay, 91405, France, (5)Earth, Environmental, and Planetary Sciences, Brown University, Box 1846, Providence, RI 02912, jbishop@seti.org
Expansive phyllosilicate deposits have been observed in the Mawrth Vallis region of Mars. The broad extent of these outcrops required a large volume of water during their formation and the similar phyllosilicate stratigraphy found across 1000 km implies a regional process governed their formation. Three primary units are present: an Fe/Mg-smectite (nontronite) unit up to 100 meters thick characterized by bands near 2.3 and 2.4 µm, a thinner ferrous material including a strong increasing slope from 1 to 2 µm, and an Al-phyllosilicate/hydrated silica unit having a band near 2.2 µm. The exposures of multiple minerals/phases including nontronite, montmorillonite, hydrated silica, kaolinite and a ferrous clay suggest an active aqueous chemistry including acid leaching or hydrothermal processes.
Spectral analyses of the ferrous component in the CRISM images of Mawrth Vallis indicate that this material most frequently occurs together with the nontronite unit below it, that it sometimes occurs in combination with the Al-phyllosilciate unit above it and that in other cases it occurs with both the Fe/Mg-OH and the Al/Si-OH features. Analyses of lab spectra of phyllosilicates and phyllosilicate mixtures suggest that some Mg/Fe2+-chlorite minerals could be mixed with nontronite and not contribute changes to the spectral feature near 2.3 µm. Other clay minerals such as illite mixed with nontronite would change the spectral features and are inconsistent with our observations at Mawrth Vallis.
Detailed examination of the Mawrth Vallis spectra is showing the presence of smaller outcrops of phyllosilicates and hydrated components. We are continuing to analyze these in order to constrain likely formation scenarios for the Mawrth Vallis region including sedimentary and pedogenic processes.
