Hematite at Meridiani Planum and Gusev Crater as identified by the Moessbauer Spectrometer MIMOS II

HR: 14:30h
AN: P13B-04 [Abstracts]
TI: Hematite at Meridiani Planum and Gusev Crater as identified by the Moessbauer Spectrometer MIMOS II
AU: * Klingelhoefer, G
EM: klingel@mail.uni-mainz.de
AF: Johannes Gutenberg-University Inst. Inorganic Chemistry, Staudinger Weg 9, Mainz, 55099 Germany
AU: Morris, R V
EM: richard.v.morris@nasa.gov
AF: Johnson Space Center, Code SR, Houston, TX 77058 United States
AU: Rodionov, D
EM: daniel@iacgu7.chemie.Uni-Mainz.DE
AF: Johannes Gutenberg-University Inst. Inorganic Chemistry, Staudinger Weg 9, Mainz, 55099 Germany
AU: Schroeder, C
EM: schroedc@uni-mainz.de
AF: Johnson Space Center, Code SR, Houston, TX 77058 United States
AU: de Souza, P A
EM: paulo.antonio.souza@cvrd.com.br
AF: CVRD, Av. Dante Micheline, Vitoria, 8001 Brazil
AU: Yen, A
EM: Albert.Yen@jpl.nasa.gov
AF: Jet Propulsion Laboratory, Oak Grove Driveÿ, Pasadena, CA 91109 United States
AU: Renz, F
EM: Franz.Renz@uni-mainz.de
AF: Johannes Gutenberg-University Inst. Inorganic Chemistry, Staudinger Weg 9, Mainz, 55099 Germany
AU: Wdowiak, T
EM: wdowiak@physics.phy.uab.edu
AF: University of Alabama, Dep. of Physics, Birmingham, AL 0000 United States
AB: The Moessbauer (MB) spectrometers on the MER rovers Opportunity and Spirit, which landed on Mars in January 2004, have identified the iron-containing mineral hematite (a-Fe2O3) at both landing sites. On Earth, hematite can occur either by itself or with other iron oxides as massive deposits, in veins , and as particles dispersed through a silicate or other matrix material. Hematite particle size can range from nanophase (superparamagnetic) to multidomain and particle shape ranges from equant to acicular to platy. Fine-grained hematite is red in color and is a pigmenting agent. Coarse-grained hematite can be spectrally neutral (gray) at visible wavelengths. Substitutional impurities, particularly Al, are common in hematite. Chemically pure, coarse-grained, and well-crystalline hematite has a magnetic transition (the Morin transition) at ~260 K. Moessbauer spectra, recorded as a function of temperature, provide a way to characterize Martian hematite with respect to some of the physical and chemical characteristics. At Meridiani Planum besides the iron-sulfate mineral jarosite also the Fe-oxide hematite has been identified by the Moessbauer spectrometer, mainly in three distinct types of reservoir: - outcrop matrix material dominated by the mineral jarosite in the MB spectrum, certain basaltic soils, and mm-sized spherules dubbed blueberries. Moessbauer spectra of each reservoir yield a distinct set of hyperfine parameters for hematite, suggesting different degrees of crystallinity and particle size. The hematite found by MB instrument MIMOS II in the outcrop material shows the Morin transition at relatively high temperatures (ca. 250 K) which is an indication of pure and well-crystallized hematite. The source of the hematite in the `Blueberries' as identified by Moessbauer spectroscopy, and also by MiniTES, is not known. These spherules, covering nearly the whole landing site area (Eagle crater, plains, Endurance crater), may be concretions formed in the outcrop involving aqueous processes. They are dispersed throughout the hematite containing jarositic outcrop material. According to Moessbauer analysis the dominating iron-bearing mineral in the spherules is hematite, and jarosite not been detected so far in significant amounts. But there are some places with hematite showing characteristics different from the hematite described above: (1) the soil at B023-HematiteSlope-Hema2 has some blueberries, but the MB did not seem to intercept any. The temperature dependence of its MB parameteres are different from those of blueberries. (2) B049-RasberryNewton-Filling shows a unique Hm MB signature, as well as (3) B051-RealSharksTooth-Enamel1. At Gusev Crater no widespread occurrence of hematite has been detected on the Gusev plains, although minor amounts of hematite were detected in an alteration rind on the rock Mazatzal at the rim of Bonneville crater. At the Columbia Hills, however, the MB instrument did find hematite in significant amounts in highly altered rocks, showing at the same time a significant decrease in the amount of olivine compared to typical basaltic rocks at Gusev crater.
DE: 5415 Erosion and weathering
DE: 5470 Surface materials and properties
DE: 6225 Mars
DE: 3672 Planetary mineralogy and petrology (5410)
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting