HR: 1340h
AN: P13A-1041    [Abstracts]
TI: Chemical And Physical Properties Of Diverse Basalts From Gusev Crater, Mars: Implications For A Heterogeneous Martian Mantle
AU: * Schmidt, M E
EM: schmidtm@si.edu
AF: Smithsonian Institution, Natural History Museum 10th and Constitution Ave, NW, Washington, DC 20560, United States
AU: McCoy, T J
EM: mccoyt@si.edu
AF: Smithsonian Institution, Natural History Museum 10th and Constitution Ave, NW, Washington, DC 20560, United States
AU: Crumpler, L S
EM: larry.crumpler@state.nm.us
AF: New Mexico Museum of Natural History, 1901 Mountain Rd, NW, Albuquerque, NM 87104, United States
AU: Mittlefehldt, D W
EM: David.W.Mittlefehldt@nasa.gov
AF: NASA Johnson Space Center, Mail Code SX3 2101 NASA Road 1, Houston, TX 77058, United States
AU: Morris, R V
EM: richard.v.morris@nasa.gov
AF: NASA Johnson Space Center, Mail Code SX3 2101 NASA Road 1, Houston, TX 77058, United States
AU: Gellert, R
EM: ralf@physics.uoguelph.ca
AF: Dept of Physics University of Guelph, MacNaughton Building Gordon Street, Guelph, ON N1G 2W1, Canada
AB: Since arriving in the basalt-dominated Gusev Crater, the Mars Exploration Rover Spirit has discovered three groups of basalt lavas (44.5 to 49.5 wt% SiO2) that were distinguished by alkali concentration and Fe- mineralogy. 1) The Adirondack class olivine-rich basalts, found in the Gusev Plains surrounding the Columbia Hills contain 0-8% microvesicles and 5-10% light-toned phenocrysts. 2) The Backstay class consists of massive float olivine pyroxene basalt on Husband Hill. 3) The Irvine class magnetite pyroxene basalts were first identified as a massive float rock on Husband Hill, but also make up mounds and ridges of monolithologic vesicular basalts (20-40% vesicles) in the Inner Basin of the Columbia Hills. All three basalt groups are Fe-rich (13-20 wt% total Fe as FeO*) and Al2O3-poor (8.2 to 13.2 wt%), and would have lower viscosity (1.9 to 6.5 Pa-s anhydrous) and higher magma density (3.2-3.3 g/cm3) relative to terrestrial basalts. The low viscosity and high vesicularity of the basalts in the Inner Basin suggest that they solidified close to their vent source. No intact lava flow has been identified, however and field exposures consist of basalt blocks up to 1 m across. Alkali concentrations of the Gusev basalts range to higher concentrations than has been observed elsewhere on Mars, including the Viking and Pathfinder landing sites and the SNC Martian meteorites. Total alkalis vary from 2.6-3.1% and 3.3-3.9% for the subalkaline Adirondack and Irvine classes, respectively and up to 5.2% for the alkaline Backstay class. McSween and others (2006) suggest that the observed diversity in alkalis in Gusev basalts resulted from the fractional crystallization and concentration of incompatible elements (including alkalis and volatiles) of an Adirondack composition magma. Vesicles record primary outgassing of the Mars interior and support higher volatile concentrations in the alkali-rich Irvine class magmas. However the fractional crystallization model would require a single repeatable batch of magma over the volcanically active history of Gusev Crater (~1 billion years; Grant et al, 2006). Different degrees of partial melting may also result in magmas with variable alkali concentrations. Alternatively, the concentration of alkali-rich basalts may reflect the tapping of an enriched mantle domain with higher concentrations of alkali and volatile elements beneath Gusev Crater. Mantle homogenizing processes, such as plate tectonics and mantle convection do not occur on Mars; signifying that mantle heterogeneity generated during early magma ocean remains. This is supported by chemical and isotopic results from the suite of Martian meteorites.
DE: 5480 Volcanism (6063, 8148, 8450)
DE: 6225 Mars
DE: 8425 Effusive volcanism
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting