HR: 1340h
AN: P13D-1559    [Abstracts]
TI: Layering of Al- and Fe/Mg-phyllosilicates in Western Mawrth Vallis, Mars, and Implications for Aqueous Processes During the Noachian Period
AU: * Bishop, J L
EM: Janice.L.Bishop@nasa.gov
AF: SETI Institute/NASA-ARC, 515 N Whisman Rd, Mountain View, CA 94043, United States
AU: Noe Dobrea, E
AF: Jet Propulsion Laboratory/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109, United States
AU: McKeown, N
AF: Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, United States
AU: Mustard, J F
AF: Department of Geological Sciences, Brown University, Providence, RI 02912, United States
AU: Ehlmann, B L
AF: Department of Geological Sciences, Brown University, Providence, RI 02912, United States
AU: Milliken, R E
AF: Jet Propulsion Laboratory/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109, United States
AU: Murchie, S L
AF: JHU/Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States
AU: Bibring, J
AF: IAS, University of Paris, Orsay, 91405, France
AU: Poulet, F
AF: IAS, University of Paris, Orsay, 91405, France
AU: Malaret, E
AF: Applied Coherent Technology, Inc., 112 Elden St., Herndon, VA 20170, United States
AU: Hash, C
AF: Applied Coherent Technology, Inc., 112 Elden St., Herndon, VA 20170, United States
AU: Team, C
AB: Phyllosilicates are abundant in the Mawrth Vallis outflow channel region and occur in layers, knobs and craters. This project builds on previous studies of the Mawrth Vallis region using OMEGA spectra [1,2,3], where a combination of hydrated material, Al-rich phyllosilicates, and Fe-rich phyllosilicates were observed. For this study we are focusing on the region west of the major outflow channel where phyllosilicates occur in discrete layers associated with the stratigraphy. Mars Express OMEGA and Mars Reconnaissance Orbiter CRISM and CTX images are investigated in parallel in order to identify specific phyllosilicate minerals and map these within the Noachian terrain. CRISM multispectral data sampled at 256 pixels per degree and map projected into 5-degree tiles, plus high resolution hyperspectral images HRL43EC and FRT672C are available to date and have been analyzed here. We observe three distinct types of phyllosilicate-bearing layers. One is an Al-phyllosilicate with a band near 2.20-2.21 um that is consistent with montmorillonite and kaolinite, and another is an Fe/Mg- phyllosilicate exhibiting bands at 2.30 and 2.39 um, which are consistent with ferrosaponite. A third layer is characterized by a broad Fe²⁺ slope, possibly due to ferrous mica, and a broad band near 2.2-2.27 um that could be due to hydrated silica or glass or poorly crystalline AlSi-bearing phases. Although montmorillonite is the spatially dominant Al-phyllosilicate over most of the Mawrth Vallis region, kaolinite is also identified in ~100 m x 100 m patches in some areas. The presence of kaolinite south and west of the mouth of the valley, but not further south along the outflow channel [4], possibly indicates longer periods of aqueous activity and more highly altered material in the western region. The presence of ferrous mica would also imply the presence of more water than other clay minerals commonly require. In many locations the Fe²⁺-bearing layer often occurs in between the Al-phyllosilicate and Fe/Mg-phyllosilicate layers. The stratigraphic sequence consists of, from bottom to top: (i) a dark and relatively smooth Fe/Mg-rich phyllosilicate layer that is partially covered by (ii) a brighter and rougher layer containing a ferrous material plus a hydrated phase, then (iii) a bright layer with a rough surface containing Al-phyllosilicate, and finally (iv) a dark, rough-textured mantling unit on top. One of the simpler explanations for the occurrence of these three phyllosilicate-bearing layers is changes in the aqueous chemistry and/or depositional environment over time during the Noachian period such that different phyllosilicate minerals formed and were deposited in layers. [1] Poulet et al. (2005) Nature, 438, 632-627. [2] Loizeau et al. (2007) JGR, 112, E08S08, doi:10.1029/2006JE002877. [3] Noe Dobrea and Michalski (2006) AGU Fall Mtg, abs.#P23D-0091. [4] Wray et al. (2007) 7th Mars Conf., abs.#3119.
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 5464 Remote sensing
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting