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Fine-grained Goethite as a Precursor for Martian Gray HematiteSeveral isolated deposits of gray, crystalline hematite on Mars were discovered using data returned from the Thermal Emission Spectrometer (TES) instrument aboard the Mars Global Surveyor spacecraft. Christensen et al. provided five testable hypotheses regarding the formation of crystalline hematite on Mars: 1) low-temperature precipitation of Fe oxides/hydroxides from standing, oxygenated, Fe-rich water, followed by subsequent alteration to gray hematite, 2) low-temperature leaching of iron-bearing silicates and other materials leaving a Fe-rich residue laterite-style weathering) which is subsequently altered to gray hematite, 3) direct precipitation of gray hematite from Fe-rich circulating fluids of hydrothermal or other origin, 4) formation of gray hematitic surface coatings during weathering, and 5) thermal oxidation of magnetite-rich lavas. Since this initial work, several authors have examined the hematite deposits to determine their formation mechanism. Lane et al. cited the absence of a 390/ cm absorption in the martian hematite spectrum as evidence for platy hematite grains. Their model for the formation of the deposits includes deposition of any of a variety of iron oxides or oxyhydroxides by aqueous or hydrothermal fluids, burial and metamorphosis to gray platy hematite grains, and exhumation in recent times. Based on a detailed geomorphic examination of the Sinus Meridiani region, Hynek et al. conclude that the most likely method of hematite formation was either emplacement by a hydrothermal fluid or oxidation of a magnetite-rich pyroclastic deposit. Similarly, Arvidson et al., favor a model involving the alteration of pyroclastic deposits by aqueous or hydrothermal fluids. Finally, based on geochemical modeling and an examination of Aram Chaos, Catling and Moore favor emplacement by hydrothermal fluids with a minimum temperature of 100 C. Comparison of the average martian hematite spectrum measured by TES to hematite emissivity spectra for a variety of naturally occurring hematites shows small but potentially important differences. In particular, band shapes, positions and relative band emissivities of hematite spectra vary over the range of samples. These differences imply that the natural variability of thermal infrared hematite spectra has not been fully characterized, especially with respect to the reaction pathway and crystal structure.
Document ID
20030066721
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
T D Glotch
(Arizona State University Tempe, Arizona, United States)
R V Morris
(Johnson Space Center Houston, Texas, United States)
T G Sharp
(Arizona State University Tempe, Arizona, United States)
PR Christensen
(Arizona State University Tempe, Arizona, United States)
Date Acquired
August 21, 2013
Publication Date
July 25, 2003
Publication Information
Publication: Sixth International Conference on Mars
Publisher: LPI
Subject Category
Lunar And Planetary Science And Exploration
Report/Patent Number
3188
Meeting Information
Meeting: Sixth International Conference on Mars
Location: Pasadena, CA
Country: US
Start Date: July 20, 2003
End Date: July 25, 2003
Sponsors: Lunar and Planetary Institute
Funding Number(s)
WBS: NCC5-679
Distribution Limits
Public
Copyright
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