HR: 0800h
AN: V21B-0611    [Abstracts]
TI: The Possible Effect of Benches and Convective Flow Segregation in Creating Mineral Layers in Intrusive Sheets: A Model for the Palisades Sill
AU: * Rice, A
EM: aar80@columbia.edu
AF: Dept of Earth and Planetary Sciences, American Museum of Natural History, 79th St and Central Park West, New York, NY 10024 United States
AU: van Wyk, S
EM: arice@amnh.org
AF: Dept of Earth and Planetary Sciences, American Museum of Natural History, 79th St and Central Park West, New York, NY 10024 United States
AU: Block, K
EM: kblock@sci.ccny.cuny.edu
AF: Department of Earth and Atmospheric Sciences, City College of New York, CUNY, 138th and Convent Avenue J106, New York, NY 10031 United States
AU: Block, K
EM: kblock@sci.ccny.cuny.edu
AF: PhD Program in Earth and Environmental Sciences, City University of New York, 365 5th Avenue, New York, NY 10016 United States
AU: Steiner, J
EM: steiner@sci.ccny.cuny.edu
AF: Department of Earth and Atmospheric Sciences, City College of New York, CUNY, 138th and Convent Avenue J106, New York, NY 10031 United States
AU: Steiner, J
EM: steiner@sci.ccny.cuny.edu
AF: PhD Program in Earth and Environmental Sciences, City University of New York, 365 5th Avenue, New York, NY 10016 United States
AB: Recent mapping of the Palisades eruptive sheet of New York and New Jersey along strike defines a mafic horizon with MgO\# (56-60), Cr ($>$500 ppm), and an internal quench horizon marked by a decrease in grain size of approximately 20%. The mafic horizon pinches northward leading to a quenching of a hypersthene-phyric horizon at the level of Piermont, New York. Analyses of the sandwich horizon are consistent with fractionation of pyroxene and plagioclase and lead to a subdivision of the more felsic granophyre into a sediment-derived partial melt and basic pegmatite fractions (crystals to 2 cm). Lack of a distinctive positive Eu anomaly separate the bulk of the Palisades sections from the section at the George Washington Bridge. This is consistent with flow-injection models that create a pre-or syn-intrusion segregation of mafic materials followed by convection overturns. We suggest that basic and ultramafic igneous sheets may become stratified by encountering benches or simply through ordinary internal mechanical differentiation processes driven by flow segregation. Mechanical differentiation processes in lavas and magmas are modeled using the unrestricted Navier Stokes equations in both 2D and 3D as applied successfully to the formation of zoning in the Bushveld complex and in Komatiite flows. In contrast to the Bushveld complex that spans almost 7000 to 10000 meters, the Palisades Sill averages approximately 300 meters in depth and the classical range along strike of the olivine zone within a sheet-like body (from the George Washington Bridge Section to approximately Haverstraw New York) is almost 25 kilometers. Previous assessment that the hyalosiderite dolerite portion appears to occur in a topographic low leads to the suggestion that a perturbation in the wall rock of the intrusion, such as downfaulted block, may trigger the development of a mineralogical layer as a manifestation of eddying behind the block during the flow period in which the magma is emplaced. Arguments for a centered olivine zone, i.e., a D shaped distribution, have given no theoretical structure to date. There is field evidence for D-shape, but also for S-shape distributions. The two models are not inconsistent. The D-Shape model suggests that the suspended olivine may be driven by dispersive pressure to the center of the conduit. Some of the S-shape intrusions may reflect variations on a suspended load. Both situations may well be manifestations of the flow regimes that attended the emplacement of the magma as they both arise in the mathematical modeling.
DE: 1749 Volcanology, geochemistry, and petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting