Phyllosilicate Diversity and Past Aqueous Activity Revealed at Mawrth Vallis, Mars
Janice L. Bishop,1*
Eldar Z. Noe Dobrea,2
Nancy K. McKeown,3
Mario Parente,4
Bethany L. Ehlmann,5
Joseph R. Michalski,6
Ralph E. Milliken,2
Francois Poulet,6
Gregg A. Swayze,7
John F. Mustard,5
Scott L. Murchie,8
Jean-Pierre Bibring6
Observations by the Mars Reconnaissance Orbiter/Compact Reconnaissance
Imaging Spectrometer for Mars in the Mawrth Vallis region show
several phyllosilicate species, indicating a wide range of past
aqueous activity. Iron/magnesium (Fe/Mg)–smectite is observed
in light-toned outcrops that probably formed via aqueous alteration
of basalt of the ancient cratered terrain. This unit is overlain
by rocks rich in hydrated silica, montmorillonite, and kaolinite
that may have formed via subsequent leaching of Fe and Mg through
extended aqueous events or a change in aqueous chemistry. A
spectral feature attributed to an Fe
2+ phase is present in many
locations in the Mawrth Vallis region at the transition from
Fe/Mg-smectite to aluminum/silicon (Al/Si)–rich units.
Fe
2+-bearing materials in terrestrial sediments are typically
associated with microorganisms or changes in pH or cations and
could be explained here by hydrothermal activity. The stratigraphy
of Fe/Mg-smectite overlain by a ferrous phase, hydrated silica,
and then Al-phyllosilicates implies a complex aqueous history.
2 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
3 Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA 95064, USA.
4 Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
5 Department of Geological Sciences, Brown University, Providence, RI 02912, USA.
6 Institut d'Astrophysique Spatiale, Orsay, 91405, France.
7 U.S. Geological Survey, Denver, CO 80225, USA.
8 Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
* To whom correspondence should be addressed. E-mail: jbishop{at}seti.org
