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    Geochemistry of crustally derived leucocratic igneous rocks from the Ulugh Muztagh Area, Northern Tibet and their implications for the formation of the Tibetan Plateau

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    WalkerJ_JGR_95(B13)21483.pdf (1.863Mb)
    Issue Date
    1990-12-10
    Author
    McKenna, L. W.
    Walker, J. Douglas
    Publisher
    American Geophysical Union
    Type
    Article
    Article Version
    Scholarly/refereed, publisher version
    Metadata
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    Abstract
    Igneous rocks collected from the Ulugh Muztagh, 200 km south of the northern rim of the Tibetan Plateau (36°28′N, 87°29′E), form intrusive and extrusive bodies whose magmas were produced by partial melting of upper-crustal, primarily pelitic, source rocks. Evidence for source composition includes high initial 87Sr/86Sr ratios (∼0.711 to 0.713), 206Pb/204Pb ratios of 18.72, 207Pb/204Pb of 15.63 and 208Pb/204Pb of 38.73. The degree of melting in the source region was increased by significant heating via in situ decay of radioactive nuclides; a reasonable estimate for the heat production rate in the source is 3.9×10−6 W/m3. The crystallization ages and cooling ages [Burchfiel et al., 1989] of the earliest intrusive rocks within the suite suggest crustal thickening began in the northern Tibetan Plateau before 10.5 Ma, with maximum average unroofing rates in this part of the Tibetan Plateau for the period between 10.5 and 4 Ma at approximately < 2 mm/yr. The Ulugh Muztagh flows are at the northern edge of a widely distributed field of Plio-pliestocene volcanic rocks in the north-central Tibetan Plateau. The crustally derived rocks described here are an endmember component of a wide mixing zone of hybrid magmas; the other end-member forms mantle-derived, potassic basanites and tephrites exposed in the central section of the Plio-Pleistocene field. The compositional trends in these belts strike east-west, at high angle to the N30E strike of the Plateau itself. Consideration of the chemical data and published geophysical data argue that the sub-Plateau mantle is mechanically detached from the overlying continental lithosphère, and that in this section of the plateau the thermal structure of the asthenosphere is not responsible for the formation or maintenance of the plateau's topography.
    Description
    This is the published version. Copyright 2012 American Geophysical Union. All Rights Reserved.
    URI
    http://hdl.handle.net/1808/17133
    DOI
    https://doi.org/10.1029/JB095iB13p21483
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    • Geology Scholarly Works [247]
    Citation
    McKenna, L. W., and J. D. Walker (1990), Geochemistry of crustally derived leucocratic igneous rocks from the Ulugh Muztagh Area, Northern Tibet and their implications for the formation of the Tibetan Plateau, J. Geophys. Res., 95(B13), 21483–21502, http://dx.doi.org/10.1029/JB095iB13p21483.

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    Contact KU ScholarWorks
    785-864-8983
    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    785-864-8983

    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    Image Credits
     

     

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