HR: 10:50h
AN: P12A-03 INVITED     [Abstracts]
TI: Aqueous Alteration in the Columbia Hills of Gusev Crater, Mars: Geochemical and Mineralogical Properties
AU: * Ming, D W
EM: douglas.w.ming@nasa.gov
AF: NASA Johnson Space Center, Astromaterials Research and Exploration Science Directorate, Houston, TX 77058 United States
AU: Morris, R V
EM: richard.v.morris@nasa.gov
AF: NASA Johnson Space Center, Astromaterials Research and Exploration Science Directorate, Houston, TX 77058 United States
AB: Water played a major role in the formation and alteration of rocks, outcrops, and soils in the Columbia Hills. The extent of alteration ranges from moderately to extensively altered materials. Six distinct rock compositional classes have been identified in the Columbia Hills (Clovis, Wishstone, Peace, Watchtower, Backstay, and Independence) and the rover wheels uncovered one unusual soil (Paso Robles). Clovis class rocks have elemental compositions similar to Gusev plains soil but with higher Mg, Cl, and Br and lower Ca and Zn; Wishstone and Watchtower classes have high Al, Ti and P and low Cr, Ni and Br; Peace has high Mg and S and low Al, Na, and K; Backstay basalts have high Na and K compared to Adirondack basalts on the plains; Independence has high Si; and the Paso Robles soil has high S and P. Some rocks are corundum-normative indicating that their primary compositions were changed by loss and/or gain of "rock-forming" elements. The changes in primary igneous compositions likely result from aqueous alteration under open hydrologic systems. Mineralogical compositions were determined directly from Moessbauer and thermal emission spectra and inferred from inter-element correlations. Clovis materials consist of Fe-oxides/oxyhydroxides (magnetite, nanophase ferric oxides (np-Ox), hematite, goethite), Ca-phosphates, Ca-sulfates, pyroxene-like phases and secondary aluminosilicates. Wishstone and Watchtower rocks consist of Fe-oxides/oxyhydroxides, ilmenite, Ca-phosphates, pyroxene, feldspar, Mg-sulfates, and secondary aluminosilicates. Peace outcrop consists of magnetite, np-Ox, Mg- and Ca-sulfates, pyroxene, olivine, feldspar, apatite, chlorides, and secondary aluminosilicates. Independence class rocks consist mostly of secondary aluminosilicates along with Ca- and Mg-sulfates, np-Ox, ilmenite, and Ca-phosphates. Backstay is relatively unaltered basalt with a composition near the trachybasalt-basaltic trachyandesite boundary, and is best classified as a martian equivalent of hawaiite-mugearite. The Paso Robles soil consists of Fe(III)-, Mg-, Ca- and minor-element sulfates, Ca-phosphates, hematite, halite, allophane, and amorphous Si. Columbia Hills outcrops and rocks may have formed by the alteration of basaltic rocks, volcaniclastic materials, and/or impact ejecta by solutions that were rich in acid-volatile elements. However, it is not clear whether aqueous alteration occurred by metasomatism, hydrothermal solutions associated with volcanic or impact processes, aqueous vapors from volcanic emanations (i.e., acid fog weathering), and/or by low-temperature solutions.
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
DE: 3617 Alteration and weathering processes (1039)
DE: 3672 Planetary mineralogy and petrology (5410)
DE: 5220 Hydrothermal systems and weathering on other planets
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: Fall Meeting 2005