HR: 1340h
AN: P23A-1094    [Abstracts]
TI: Evidence for possible widespread alteration of basaltic terrains on Mars
AU: * Bandfield, J L
EM: joshband@asu.edu
AF: Arizona State University, P.O. Box 876305, Tempe, AZ 85283-6305, United States
AU: Rogers, A D
EM: deanne.rogers@gmail.com
AF: Stony Brook University, 255 Earth and Space Sciences Building (ESS), Stony Brook, NY 11794-2100, United States
AB: Thermal infrared spectral data returned from the THEMIS instrument on the Mars Odyssey Spacecraft display localized variations in the olivine content in northeast Argyre Planitia. Isolated hills and rough terrain near the crater rim have both high olivine concentrations up to 20% and high thermal inertia values consistent with coarse particulate materials or bedrock exposures. Numerous gullies are often located on the slopes of this rough terrain that appear to have transported material from the olivine rich terrain to the relatively flat surrounding plains. The material within the gullies and plains is significantly depleted in olivine content relative to the olivine rich source terrain. However, the plains do not contain significant alteration products visible in either TES or OMEGA spectral datasets and are consistent with basaltic surfaces. These observations imply that surfaces that have been characterized as relatively unaltered basalts based on orbital spectroscopic observations may instead have been significantly altered since the time of their formation. This region displays this relationship particularly well, but a similar pattern appears to be widespread on Mars. High thermal inertia units associated with rocks or bedrock outcrops, such as Ares Valles, Gusev Crater, and Nili Fossae are typically enriched in olivine relative to the surrounding lower inertia regolith. It is possible that the process responsible for producing the Martian regolith involves a significant amount of compositional alteration through weathering or winnowing. For example, the weathering environment on Mars has been hypothesized to be highly conducive to the dissolution of olivine much more rapidly than other common minerals on Mars such as pyroxene and plagioclase. A possible implication of these observations is that altered surfaces are much more common than previously acknowledged on Mars. In addition, exposures of unaltered igneous compositions may be relatively rare and limited to isolated windows.
DE: 5410 Composition (1060, 3672)
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
DE: 5494 Instruments and techniques
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting