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Detailed Reference Information |
Condie, K.C. (2003). Incompatible element ratios in oceanic basalts and komatiites: Tracking deep mantle sources and continental growth rates with time. Geochemistry Geophysics Geosystems 4: doi: 10.1029/2002GC000333. issn: 1525-2027. |
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Ratios of elements with similar incompatibilities in the mantle can be used to characterize magma sources through time. Nb/Y and Zr/Y distributions in oceanic basalts support the existence of a long-lived, deep depleted source in mantle. Zr/Y, Nb/Y, Zr/Nb, and Nb/Th ratios in oceanic basalts and komatiites suggest that depleted and recycled components, together probably with an enriched component, were present in the deep mantle by 3.5 Ga. Low Zr/Nb and Hf/Sm ratios and high La/Yb and Nb/Y ratios in some plume basalts and Al-depleted komatiites may reflect majorite fractionation. High Zr/Nb ratios and low Nb/Y ratios in Archean Al-undepleted komatiites may record partial melting of a Mg-perovskite source in deep mantle plumes in which Mg-perovskite crystallizes and accumulates in komatiite melts during ascent. Oceanic greenstone basalts show a gradual increase in the Nb/Th ratio with time with a relatively sudden increase at about 2 Ga. This trend is consistent with gradual continental growth and with a major episode of continental growth at 2.7 Ga. Nb/Th ratios in some Early Archean basalts may record extraction of up to 25% of the present volume of continental crust from the early upper mantle. An alternative explanation for the rapid increase in Nb/Th in oceanic basalts at 2 Ga is that a catastrophic 2.7-Ga event in the mantle changed the composition or/and location of the primary volume of mantle from which continental crust was extracted. |
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Abstract |
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Keywords
Geochemistry, Chemical evolution, Geochemistry, Trace elements, Global Change, Solid Earth, Tectonophysics, Evolution of the Earth |
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Journal
Geochemistry Geophysics Geosystems |
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Publisher
American Geophysical Union 2000 Florida Avenue N.W. Washington, D.C. 20009-1277 USA 1-202-462-6900 1-202-328-0566 service@agu.org |
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