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Identification of hydrated silicate minerals on Mars using MRO-CRISM: Geologic context near Nili Fossae and implications for aqueous alteration

Ehlmann, Bethany L. and Mustard, John F. and Swayze, Gregg A. and Clark, Roger N. and Bishop, Janice L. and Poulet, Francois and Des Marais, David J. and Roach, Leah H. and Milliken, Ralph E. and Wray, James J. and Barnouin-Jha, Olivier and Murchie, Scott L. (2009) Identification of hydrated silicate minerals on Mars using MRO-CRISM: Geologic context near Nili Fossae and implications for aqueous alteration. Journal of Geophysical Research E, 114 . Art. No. E00D08. ISSN 0148-0227. http://resolver.caltech.edu/CaltechAUTHORS:20121016-082328715

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Abstract

The Noachian terrain west of the Isidis basin hosts a diverse collection of alteration minerals in rocks comprising varied geomorphic units within a 100,000 km2 region in and near the Nili Fossae. Prior investigations in this region by the Observatoire pour l'Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) instrument on Mars Express revealed large exposures of both mafic minerals and iron magnesium phyllosilicates in stratigraphic context. Expanding on the discoveries of OMEGA, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) has found more spatially widespread and mineralogically diverse alteration minerals than previously realized, which represent multiple aqueous environments. Using CRISM near-infrared spectral data, we detail the basis for identification of iron and magnesium smectites (including both nontronite and more Mg-rich varieties), chlorite, prehnite, serpentine, kaolinite, potassium mica (illite or muscovite), hydrated (opaline) silica, the sodium zeolite analcime, and magnesium carbonate. The detection of serpentine and analcime on Mars is reported here for the first time. We detail the geomorphic context of these minerals using data from high-resolution imagers onboard MRO in conjunction with CRISM. We find that the distribution of alteration minerals is not homogeneous; rather, they occur in provinces with distinctive assemblages of alteration minerals. Key findings are (1) a distinctive stratigraphy, in and around the Nili Fossae, of kaolinite and magnesium carbonate in bedrock units always overlying Fe/Mg smectites and (2) evidence for mineral phases and assemblages indicative of low-grade metamorphic or hydrothermal aqueous alteration in cratered terrains. The alteration minerals around the Nili Fossae are more typical of those resulting from neutral to alkaline conditions rather than acidic conditions, which appear to have dominated much of Mars. Moreover, the mineralogic diversity and geologic context of alteration minerals found in the region around the Nili Fossae indicates several episodes of aqueous activity in multiple distinct environments.


Item Type:Article
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http://dx.doi.org/10.1029/2009JE003339DOIUNSPECIFIED
http://www.agu.org/pubs/crossref/2009/2009JE003339.shtmlPublisherUNSPECIFIED
Additional Information:© 2009 American Geophysical Union. Received 23 January 2009; accepted 11 June 2009; published 23 October 2009. Mario Parente and Frank Seelos provided numerous useful suggestions on data analysis for this manuscript. Thanks to Lynn Carlson, Nicolas Mangold, and Nancy McKeown for helpful advice on techniques for combining data sets to make geologic interpretations. We appreciate the many helpful discussions with members of the CRISM team and the ongoing, dedicated efforts of the CRISM-SOC to acquire this spectacular data set. Reviewers Brad Dalton and Victoria Hamilton provided detailed comments that improved this manuscript. We also thank the CTX and HiRISE teams for their commitment to coordinated observations which enable high-resolution studies of Mars mineralogy with morphology.
Subject Keywords:aqueous alteration; phyllosilicate; Nili Fossae
Record Number:CaltechAUTHORS:20121016-082328715
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20121016-082328715
Official Citation: Ehlmann, B. L., et al. (2009), Identification of hydrated silicate minerals on Mars using MRO-CRISM: Geologic context near Nili Fossae and implications for aqueous alteration, J. Geophys. Res., 114, E00D08, doi:10.1029/2009JE003339, [printed 115(E2), 2010].
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:34910
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:16 Oct 2012 16:15
Last Modified:27 Dec 2012 02:52

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