HR: 10:20h
AN: P12A-01    [Abstracts]
TI: Petrography of Rocks Examined by the Mars Exploration Rover Spirit within the Gusev Plains and Columbia Hills, Mars
AU: * Crumpler, L S
EM: larry.crumpler@state.nm.us
AF: New Mexico Museum of Natural History and Science, 1801 Mountain Road NW, Albuquerque, NM 87104 United States
AU: McSween, H
EM: mcsween@utk.edu
AF: Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996 United States
AB: Petrographic and megascopic textures of rocks encountered along the traverse of the Spirit Mars Exploration Rover within the Gusev plains (landing site to hills) and within the Columbia Hills (West Spur to lower Husband Hill), together with chemical data based on in situ measurements with the Athena spectrometers, provide information about the mechanisms and conditions of rock emplacement. Primary igneous and low-grade alteration textures are identified within the plains whereas clastic and alteration textures dominate within the Columbia Hills. Plains rocks include primary igneous petrographic textures common to xenocrystic and phyric rocks, megascopic textures similar to that known to occur within differing vertical positions of terrestrial basaltic lavas, and uniform chemical compositions typical of batch melted mantle rocks. Apparent vesicularity (ratio of summed vesicle volume from area over rock unit volume) of rocks in the plains lava surface varied with host rock dimension and angularity. Vesicle distributions in the smaller clasts in the Gusev plains tend to be exponential, typical of upper sections, whereas, dis-tributions in larger, more angular Gusev plains blocks are characterized by hybrid distri-butions, typical of flow interiors. Since small vesicular clasts are a small fraction of the observed clast population, it is inferred that the upper vesicular zones within the Gusev plains lava flows were rela-tively thin (low vesicularity at shallow depths) compared with that predicted for lava flows on Earth. A thin upper vesicular zone in the Gusev plains lavas could be indirect evidence for atmospheric pressure close to current values at the time of Gusev plains basalt emplacement during the Hesperian. Rocks with volcaniclastic or impactite textures occur in outcrops visited within the Columbia Hills. Megascopic and microscopic (Microscopic Imager) textures were examined along apparent lamination planes at several outcrops of moderately consolidated, fine-grained rocks. Some rocks contain distinct matrix-supported, sub-round lithic or crystal fragments yet little evidence of vertical gradation or sorting. Texturally simple and bearing textures indicative of energetic emplacements, these rocks are complex chemically, suggesting derivation from multiple protoliths or variable alteration of a limited range of lithologies.
DE: 1090 Field relationships (3690, 8486)
DE: 5220 Hydrothermal systems and weathering on other planets
DE: 5470 Surface materials and properties
DE: 5480 Volcanism (6063, 8148, 8450)
DE: 8486 Field relationships (1090, 3690)
SC: Planetary Sciences [P]
MN: Fall Meeting 2005