The La/Nb ratio (< 1.4) and the Ni concentration (> 30 ppm at a Mg number of 40) in oceanic plateau basalts and MORB provide a useful index to distinguish them from are basalts. MORE can generally be distinguished from plateau basalts by their lower Nb contents (< 3 ppm) and lower Nb/Y ratios (< 0.1). The La/Nb ratio and Ni contents of mafic lower crustal xenoliths indicate that at most xenolith sites, both are and plume-related components occur in the lower crust. Considered as a whole, mafic xenolith data suggest that about one third of the post-Archean lower continental crust is composed of mafic rocks from mantle plume sources (accreted oceanic plateaus or mafic underplate), and the remainder come chiefly from are sources. Because both crustal and host magma contamination should raise La/Nb ratios in xenoliths, the value of one third is a minimum for the plume component in the lower crust. (C) 1999 Elsevier Science B.V. All rights reserved.
机构:
State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, BeijingState Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing
Zhang Y.
Zhai M.
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State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing
College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, BeijingState Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing
Zhai M.
Zhou Y.
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State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing
College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, BeijingState Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing
Zhou Y.
Zhou L.
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State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, BeijingState Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing
机构:
Univ Calif Santa Barbara, Dept Earth Sci, Santa Barbara, CA 93106 USAUniv Calif Santa Barbara, Dept Earth Sci, Santa Barbara, CA 93106 USA
Hacker, Bradley R.
Kelemen, Peter B.
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Columbia Univ, Lamont Doherty Earth Observ, Dept Earth & Environm Sci, Palisades, NY 10964 USAUniv Calif Santa Barbara, Dept Earth Sci, Santa Barbara, CA 93106 USA
Kelemen, Peter B.
Behn, Mark D.
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Woods Hole Oceanog Inst, Dept Geol & Geophys, Woods Hole, MA 02543 USAUniv Calif Santa Barbara, Dept Earth Sci, Santa Barbara, CA 93106 USA
Behn, Mark D.
ANNUAL REVIEW OF EARTH AND PLANETARY SCIENCES, VOL 43,
2015,
43
: 167
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