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A Case for Hydrothermal Gray Hematite in Aram ChaosThe Thermal Emission Spectrometer (TES) on Mars Global Surveyor has detected deposits of coarsegrained, gray crystalline hematite in Sinus Meridiani, Aram Chaos, and Vallis Marineris [1]. Detailed features in the hematite spectral signature of the Sinus Meridiani region show that the spectrum is consistent with emission dominated by crystal c-faces of hematite, implying that the hematite is specular [2]. Gray specular hematite (also known as specularite ) is a particular gray crystalline form that has intergrown, hexagonal plates with a silvery metallic luster. We believe that the key to the origin of specularite is that it requires crystallization at temperatures in excess of about 100 C. In reviewing the occurrence of gray hematite on Earth, we find no exceptions to this warm temperature requirement [3]. Thermal crystallization on Mars could occur (1) as diagenesis at a depth of a few kilometers of sediments originally formed in lowtemperature waters, or (2) as direct precipitation from hydrothermal solution. Aram Chaos has unique chaotic terrain that offers more clues to the formation of the hematite than the relatively featureless flat terrain (as seen from orbit) of Sinus Meridiani. Aram Chaos provides the opportunity to look at a combination of TES data, Mars Orbiter Camera images, and Mars Orbiter Laser Altimeter (MOLA) topography. This combination of data suggests that high concentrations of hematite were formed in planar strata and have since been exposed by erosion of an overlying light-toned, caprock. Lesser concentrations of hematite are found adjacent to these strata at lower elevations, which we interpret as perhaps a lag deposit. The topography and the collapsed nature of the chaotic terrain favor a hydrothermally charged aquifer as the original setting where the hematite formed. An alternative sedimentary origin requires post-depositional burial to a depth of ~3-5 km to induce thermally driven recrystallization of fine-grained iron oxides to coarse-grained hematite.
Document ID
20030066666
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
D C Catling
(University of Washington Seattle, Washington, United States)
J M Moore
(Ames Research Center Mountain View, California, 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
3245
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)
CONTRACT_GRANT: NCC5-679
Distribution Limits
Public
Copyright
Portions of document may include copyright protected material.
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