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Coatings on Atacama Desert Basalt: A Possible Analog for Coatings on Gusev Plains BasaltSurface coatings on Gusev Plains basalt have been observed and may contain hematite and nanophase Fe-oxides along with enrichments in P, S, Cl, and K relative to the underlying rock. The Gusev coatings may be derived from the dissolution of adhering soil and/or parent rock along with the addition of S and Cl from outside sources. Transient water for dissolution could be sourced from melting snow during periods of high obliquity, acid fog, and/or ground water (Haskin et al., 2005). Coatings on basalt in the hyper-arid (less than 2mm y(sup -1)) Atacama Desert may assist in understanding the chemistry, mineralogy and formation mechanisms of the Gusev basalt coatings. The Atacama Desert climate is proposed to be analogous to a paleo-Mars climate that was characterized by limited aqueous activity when the Gusev coatings could have formed. The objectives of this work are to (i) determine the chemical nature and extent of surface coatings on Atacama Desert basalt, and (ii) assess coating formation mechanisms in the Atacama Desert. Preliminary backscattered electron imaging of Atacama basalt thin-sections indicated that the coatings are as thick as 20 m. The boundary between the coating and the basalt labradorite, ilmenite, and augite grains was abrupt indicating that the basalt minerals underwent no chemical dissolution. The Atacama coatings have been added to the basalt instead of being derived from basalt chemical weathering. Semi-quantitative energy dispersive spectroscopy shows the coatings to be chemically homogeneous. The coating is depleted in Ca (0.9 wt% CaO) and enriched in K (1.3 wt.% K2O) and Si (69.1 wt.% SiO2) relative to the augite and labradorite grains. A dust source enriched in Si (e.g., poorly crystalline silica) and K and depleted in Ca appears to have been added to the basalt surface. Unlike the Gusev coatings, no P, S, and Cl enrichment was observed. However, Fe (3.2 wt.% FeO) was present in the Atacama coatings suggesting the present of Fe-oxides. While the chemistry of Atacama coating does not mirror the Gusev coating, the coating formation mechanism may be similar. The Atacama coatings of surface basalt are derived completely from exogenous sources. If surface Mars rocks have experienced limited wetting conditions as in the Atacama, then Mars coatings may be derived only from dissolution of material adhering to rock.
Document ID
20070031131
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Sutter, B.
(Jacobs Sverdrup Technology, Inc. Houston, TX, United States)
Golden, D. C.
(Barrios Technology, Inc. Houston, TX, United States)
Amundson, R.
(California Univ. Berkeley, CA, United States)
Chong-Diaz, G.
(Universidad Catolica del Norte Coquimbo, Chile)
Ming, D. W.
(NASA Johnson Space Center Houston, TX, United States)
Date Acquired
August 23, 2013
Publication Date
January 1, 2007
Subject Category
Lunar And Planetary Science And Exploration
Meeting Information
Meeting: Geological Society America
Location: Denver, CO
Country: United States
Start Date: October 29, 2007
End Date: October 31, 2007
Sponsors: Geological Society of America
Distribution Limits
Public
Copyright
Other

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