Characterization of phyllosilicates observed in the central Mawrth Vallis region, Mars, their potential formational processes, and implications for past climate

Author
McKeown, Nancy
Bishop, J. L.
Noe Dobrea, E. Z.
Ehlmann, B. L.
Parente, M.
Mustard, J. F.
Murchie, S. L.
Swayze, G. A.
Bibring, J.-P.
Silver, E. A.
Faculty Advisor
Date
2009
Keywords
Mawrth Vallis , phyllosilicates , CRISM
Abstract (summary)
Mawrth Vallis contains one of the largest exposures of phyllosilicates on Mars. Nontronite, montmorillonite, kaolinite, and hydrated silica have been identified throughout the region using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). In addition, saponite has been identified in one observation within a crater. These individual minerals are identified and distinguished by features at 1.38-1.42, approximately 1.91, and 2.17-2.41 mu m. There are two main phyllosilicate units in the Mawrth Vallis region. The lowermost unit is nontronite bearing, unconformably overlain by an Al-phyllosilicate unit containing montmorillonite plus hydrated silica, with a thin layer of kaolinite plus hydrated silica at the top of the unit. These two units are draped by a spectrally unremarkable capping unit. Smectites generally form in neutral to alkaline environments, while kaolinite and hydrated silica typically form in slightly acidic conditions; thus, the observed phyllosilicates may reflect a change in aqueous chemistry. Spectra retrieved near the boundary between the nontronite and Al-phyllosilicate units exhibit a strong positive slope from 1 to 2 mu m, likely from a ferrous component within the rock. This ferrous component indicates either rapid deposition in an oxidizing environment or reducing conditions. Formation of each of the phyllosilicate minerals identified requires liquid water, thus indicating a regional wet period in the Noachian when these units formed. The two main phyllosilicate units may be extensive layers of altered volcanic ash. Other potential formational processes include sediment deposition into a marine or lacustrine basin or pedogenesis.
Publication Information
McKeown, N. K., Bishop, J. L., Noe Dobrea, E. Z., Parente, M., Ehlmann, B. L., Mustard, J. F., Murchie, S. L., Bibring, J.-P., & Silver, E. A. (2009). Characterization of phyllosilicates observed in the central Mawrth Vallis region, Mars, their potential formational processes, and implications for past climate. Journal of Geophysical Research- Planets, 114(E2) E00D10, doi: 10.1029/2008JE003301.
DOI
Notes
Item Type
Article
Language
English
Rights
All Rights Reserved