Alkaline volcanic rocks from the Columbia Hills, Gusev crater, Mars

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Read Full Article (file size: 2144043 bytes) Cited by JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, E09S91, doi:10.1029/2006JE002698, 2006 Alkaline volcanic rocks from the Columbia Hills, Gusev crater, Mars H. Y. McSween Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee, USA S. W. Ruff Department of Geological Sciences, Arizona State University, Tempe, Arizona, USA R. V. Morris NASA Johnson Space Center, Houston, Texas, USA J. F. Bell III Department of Astronomy, Cornell University, Ithaca, New York, USA K. Herkenhoff Astrogeology Branch, U.S. Geological Survey, Flagstaff, Arizona, USA R. Gellert Department of Physics, University of Guelph, Guelph, Canada K. R. Stockstill Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, Hawaii, USA L. L. Tornabene Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee, USA S. W. Squyres Department of Astronomy, Cornell University, Ithaca, New York, USA J. A. Crisp Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA P. R. Christensen Department of Geological Sciences, Arizona State University, Tempe, Arizona, USA T. J. McCoy Department of Mineral Sciences, Smithsonian Institution, Washington, D. C., USA D. W. Mittlefehldt NASA Johnson Space Center, Houston, Texas, USA M. Schmidt Department of Mineral Sciences, Smithsonian Institution, Washington, D. C., USA Abstract Irvine, Backstay, and Wishstone are the type specimens for three classes of fine-grained or fragmental, relatively unaltered rocks with distinctive thermal emission spectra, found as float on the flanks of the Columbia Hills. Chemical analyses indicate that these rocks are mildly alkaline basalt, trachybasalt, and tephrite, respectively. Their mineralogy consists of Na- and K-rich feldspar(s), low- and high-Ca pyroxenes, ferroan olivine, Fe-Ti (and possibly Cr) oxides, phosphate, and possibly glass. The texture of Wishstone is consistent with a pyroclastic origin, whereas Irvine and Backstay are lavas or possibly dike rocks. Chemical compositions of these rocks plot on or near liquid lines of descent for most elements calculated for Adirondack class rocks (olivine-rich basalts from the Gusev plains) at various pressures from 0.1 to 1.0 GPa. We infer that Wishstone-, Backstay-, and Irvine-class magmas may have formed by fractionation of primitive, oxidized basaltic magma similar to Adirondack-class rocks. The compositions of all these rocks reveal that the Gusev magmatic province is alkaline, distinct from the subalkaline volcanic rocks thought to dominate most of the planet's surface. The fact that differentiated volcanic rocks were not encountered on the plains prior to ascending Husband Hill may suggest a local magma source for volcanism beneath Gusev crater. Received 3 February 2006; accepted 7 June 2006; published 23 September 2006. Keywords: alkaline; Mars; volcanic. Index Terms: 6230 Planetary Sciences: Solar System Objects: Martian satellites; 5480 Planetary Sciences: Solid Surface Planets: Volcanism (6063, 8148, 8450); 5475 Planetary Sciences: Solid Surface Planets: Tectonics (8149); 5410 Planetary Sciences: Solid Surface Planets: Composition (1060, 3672). Read Full Article (file size: 2144043 bytes) Cited by Citation: McSween, H. Y., et al. (2006), Alkaline volcanic rocks from the Columbia Hills, Gusev crater, Mars, J. Geophys. Res., 111, E09S91, doi:10.1029/2006JE002698. Copyright 2006 by the American Geophysical Union.

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