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    Geochemistry of mafic dikes and sills from the lower McCoy Mountains Formation, La Paz County, western Arizona

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    Author
    Gleason, J.D.
    Spencer, J.E.
    Richard, S.M.
    Issue Date
    1999
    Keywords
    Arizona Geological Survey Open File Reports
    cretaceous
    Jurassic
    Bisbee Basin
    Mojave desert
    Plomosa Mountains
    Granite Wash Mountains
    Arizona
    La Paz County
    McCoy Mountains
    metamorphism
    deformation
    volcanic rocks
    lava flow
    andesitic rocks
    basaltic
    Tectonic
    isotopic
    zircon
    metamorphic recrystallization
    bedrock geology
    sediments
    sills
    mafic dikes
    geochemistry
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    Citation
    Gleason, J.D., Spencer, J.E., and Richard, S.M., 1999, Geochemistry of mafic dikes and sills from the lower McCoy Mountains Formation, La Paz County, western Arizona. Arizona Geological Survey Open File Report, OFR-99-01, 24 p.
    Description
    Mafic dikes and sills intrude sediments of the Late Jurassic (Early Cretaceous?) lower McCoy Mountains Formation in western Arizona. Some units show evidence for intrusion into wet, unconsolidated sediments, indicating that intrusion was approximately contemporaneous with sedimentation. Some of the units also show evidence for subaerial crystallization, and may in fact be lava flows. Attempts to directly date these rocks have been hampered by metamorphic recrystallization and by our inability, despite repeated attempts, to extract zircons from them. Five units from the Granite Wash Mountains, and two from the Plomosa Mountains, were sampled for geochemical and isotopic study in order to place some further constraints on their tectonic setting. Major element, trace element, and isotopic data reveal a suite of high-AI basaltic to andesitic rocks that are sub-alkaline to moderately alkaline and slightly to moderately enriched in light rare-earth elements (LREE), and have epsilon Nd values ranging from +5 to -6. Two gabbroic sills from the Granite Wash Mountains have epsilon Nd of +5, indicating they were derived from depleted mantle sources. The geochemical and isotopic variation in the suite can be explained either as a product of heterogeneous mantle sources or variable interaction of depleted basalts with continental crust. These rocks appear to be transitional in composition and tectonic setting between rift-related basalts of the Bisbee basin and Jurassic diorites intruded during crustal extension in the eastern Mojave desert region.
    URI
    http://hdl.handle.net/10150/629747
    Additional Links
    http://repository.azgs.az.gov/uri_gin/azgs/dlio/1037
    Language
    en
    Series/Report no.
    OFR-99-01
    Rights
    Arizona Geological Survey. All rights reserved.
    Collection Information
    Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact azgs-info@email.arizona.edu.
    North Bounding Coordinate
    33.7687
    South Bounding Coordinate
    33.5263
    West Bounding Coordinate
    -114.215
    East Bounding Coordinate
    -113.963
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