MAGMA-BRINE INTERACTION TO PRODUCE HOME PLATE, GUSEV
CRATER
[*Mariek E. Schmidt*] (Dept. of Mineral Sciences, National Museum of Natural History,
Smithsonian Institution, 10th and Constitution Ave, NW, Washington, D.C. 20560-0119,
Ph. 202-633-1799, FAX 202-357-2476, schmidtm@si.edu); Nathalie Cabrol (NASA
Ames Research Center, Space Science Division, MS 245-3, Moffett Field, CA. 94035-
100); Timothy McCoy (Dept. of Mineral Sciences, National Museum of Natural History,
Smithsonian Institution, 10th and Constitution Ave, NW, Washington, D.C. 20560-0119);
James Rice (Arizona State University, PO Box 871404, Tempe, AZ 85287-1404; Steven
W. Squyres (Dept. of Astronomy, Space Sciences Bldg, Cornell University, Ithaca, NY
14853); R. Aileen Yingst (Space Grant Center, Department of Natural and Applied
Sciences, University of Wisconsin-Green Bay, 2420 Nicolet Drive, Green Bay, WI
54311-7001); and the MER Athena Science Team
ORAL
The most exciting discovery to date made by the Mars Exploration Rover Spirit
is Home Plate, a light-toned ~80 m. diameter, ~2 m tall platform of layered and cross-
bedded rock in the Inner Basin of the Columbia Hills of Gusev Crater (Squyres et al, in
revision). Spirit examined the Barnhill section at the north end of Home Plate from Sols
746-751. Three rocks, as float or outcrop, were analyzed by the instruments on the
rover’s arm or IDD (Instrument Deployment Device), which include the Microscopic
Imager, Alpha Particle X-Ray Spectrometer, and Moessbauer. Home Plate was found to
have a composition very similar to nearby scoriacious basalts, but with markedly higher
abundances of Cl, Br, Ge, and Zn. Elevated Ge concentrations (as high as 70 ppm) at
Home Plate are not correlated with high Ni concentrations (300 to 400 ppm). If the
source of the Ge were meteoritic, we would expect up to 5 wt% Ni, indicating a volcanic
source for the Ge at Home Plate. Micro- and macroscopic textures at Home Plate
including a bomb sag and possible accretionary lapilli are consistent with a
phreatomagmatic origin (Rice et al, this meeting).
Volcanic textures at Home Plate and its enrichment in halogen and volatile metal
elements points towards volcanic interaction with external briny groundwater. Nearby
hydrated sulfate salt soils have chemical characteristics akin to nearby rocks (Yen et al,
2007) and may be the exhalents of acidic hydrothermal vapor that separated from a Cl-
rich brine at depth. Separation of a S-rich vapor from a Cl-rich brine is a common
process in hydrothermal systems on Earth, such as at Yellowstone (Fournier, 1986). A
hydrothermal system such as this requires persistent water that may have ultimately
originated from the devolatilization of a large magma system, the flooding event at Gusev
Crater that carved out the Ma'adim Vallis canyon, or some other unknown process. The
cold, dry environment of Mars makes it likely that water resided for some time as ground
ice or porous salty slush in the near surface. Subsequently, this ground ice was melted
during volcanic activity in the Inner Basin of the Columbia Hills that produced
scoriacious basalts and the tephra that make up Home Plate.
References
Fournier, R.O., 1989, Geochemistry and dynamics of the Yellowstone National Park
hydrothermal system, Annual Review of Earth and Planetary Science, vol. 17, p.
13-53.
Rice, J. et al, 2007, The Phreatomagmatic origin of Home Plate, Volcano-Ice Interactions
on Earth and Mars abstract (this meeting).
Squyres, S.W. et al., in revision, Mars Exploration Rover Results at Home Plate, Gusev
Crater, Science.
Yen, A. et al., 2007, Composition and Formation of the Paso Robles Class Soils, Gusev
Crater, LPSC abstract #2030.
ORAL/POSTER?