HR: 1340h
AN: V13E-0599    [Abstracts]
TI: Primary Martian Mantle Melt Compositions Derived from Experimental Investigations of Olivine-Phyric Shergottites
AU: * Musselwhite, D
EM: musselwhite@lpi.usra.edu
AF: Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston, TX 77058 United States
AU: Treiman, A
EM: treiman@lpi.usra.edu
AF: Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston, TX 77058 United States
AB: The olivine-phyric basaltic shergottites (OPSs) have been recently recognized as a significant sub-group of the Martian meteorites. These rocks have many characteristics suggestive of a primitive nature such as high bulk and olivine core Mg#s. We have conducted crystallization experiments using the composition of Yamato 980459 (Y98) and NWA 1068, two important OPS specimens. Y98 has isotopic, trace element and redox features characteristic of derivation from a depleted mantle source. NWA 1068 on the other hand is unique among the OPSs having an undepleted character similar to Shertotty and Zagami. Crystallization experiments were conducted using a piston cylinder apparatus at Martian mantle pressures and temperatures. The composition of synthetic starting materials for Y98 runs were an average of published data; those for NWA1068 composition were corrected for the effects of desert weathering. The pressure assembly is comprised of a BaCO3 cell, MgO internal parts, and C-type thermocouple. Oxygen fugacity was controlled using starting material with a preset Fe2O3 content loaded into a graphite capsule. Runs were analyzed using the Cameca SX-100 electron microprobe at NASA/JSC. Results of the Y98 experiments show that the olivine cores are in equilibrium with the bulk rock, indicating that the bulk-rock composition is the same as the parent melt. Multiple saturation of the melt with olivine and a low-calcium pyroxene occurs at 11.5 to 12 kbars and 1450 ± 10°C indicating that the melt separated from the mantle at a depth of about 100 km. Results for the NWA 1068 experiments show olivines in equilibrium with the bulk composition with a higher Fo content than the natural cores. Mg/Fe exchange and mass balance calculations indicate a 0.1 weight fraction of excess cumulate olivine and allow derivation of a parental melt composition. Calculations using the MELTS program predict multiple saturation for this derived parent melt at a similar pressure to Y98. Experiments similar to ours on the Gusev Crater basalt composition found multiple saturation at a pressure of 11kbar -- nearly identical to the pressure for Y98 bulk and NWA 1068 derived parent compositions, implying a similar lithospheric thickness under Gusev Crater.
DE: 5405 Atmospheres (0343, 1060)
DE: 5410 Composition (1060, 3672)
DE: 5704 Atmospheres (0343, 1060)
DE: 5709 Composition (1060)
DE: 6005 Atmospheres (1060)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005