HR: 0800h
AN: P11A-0952    [Abstracts]
TI: The peridotitic laterites of New Caledonia: a possible analogue for the Martian regolith ?
AU: * Nzokwe, G Y
EM: gerry01@siu.edu
AF: Southern Illinois University at Carbondale, Department of Geology - MC4324, Carbondale, IL 62901 United States
AU: Ferre, E C
EM: eferre@geo.siu.edu
AF: Southern Illinois University at Carbondale, Department of Geology - MC4324, Carbondale, IL 62901 United States
AU: Fifarek, R
EM: fifarek@geo.siu.edu
AF: Southern Illinois University at Carbondale, Department of Geology - MC4324, Carbondale, IL 62901 United States
AU: Frima, C
EM: cfrima@free.fr
AF: IGAL, 71 rue Grange Colombe, Rambouillet, 78120 France
AB: Peridotites are very common in the Solar System where they generally form the mantle of rocky planets. On Earth, large volumes of peridotites are brought to the surface as obduction ophiolites (Oman, Newfoundland, Papua, New Caledonia). Such peridotites interact with various aqueous fluids throughout their geologic history. High temperature serpentinization (up to $600\deg$C) begins at the ocean ridge with seawater, followed by low temperature serpentinization (below $400\deg$C) away from the ridge. The obduction process generally leads to further alteration by continental aqueous fluids along structural discontinuities. Finally, exposure to the surface results in supergene serpentinization, the formation of weathering rinds, and the development of soils on peridotites that, particularly under hot and humid climates, leads to the formation of peridotitic laterites. The peridotitic laterites of New Caledonia provide excellent opportunities for geoscience investigations because, due to nickel mining, borehole cores through alteration profiles are available. The peridotite nappe, emplaced in the late Eocene, has an estimated thickness up to 3 km and is exposed over an area of 8000 km$^{2}$. Common lithologies include harzbugite, dunite, wherlite and cumulate gabbro. Regardless of the bedrock lithology, the lateritic profiles display an increase in concentration of Fe oxides and hydroxides towards the top. The alteration paths of distinct bedrock types tend to converge toward the same mineralogy. Low-field and high-field magnetic techniques have been combined to refine the vertical zonation of the lateritic profiles into distinct horizons. Magnetite is the main component in the magnetic susceptibility budget while hematite controls the coercivity. Several distinguishing features are observed in peridotitic laterites: 1) bulbous hematite concretions, 2) reddish fine-grained hematite, 3) gray flaky specular hematite (up to 10 mm in length), 4) ferricretes and manganocretes, and 5) preservation of olivine grains in spite of intense alteration in zones of high relief. Similar characteristics have been deduced from the MGS TES data or observed directly by the Mars Rovers. These results highlight the possibility that some of Martian surface features might have been inherited from a wet past and that some of the regolith may have developed from altered peridotites.
DE: 5440 Magnetic fields and magnetism
DE: 5470 Surface materials and properties
DE: 3672 Planetary mineralogy and petrology (5410)
DE: 1030 Geochemical cycles (0330)
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting