Mantle Plumes and Entrainment: Isotopic Evidence

Science  24 Apr 1992:
Vol. 256, Issue 5056, pp. 517-520
DOI: 10.1126/science.256.5056.517


Many oceanic island basalts show sublinear subparallel arrays in Sr-Nd-Pb isotopic space. The depleted upper mantle is rarely a mixing end-member of these arrays, as would be expected if mantle plumes originated at a 670-kilometer boundary layer and entrained upper mantle during ascent. Instead, the arrays are fan-shaped and appear to converge on a volume in isotopic space characterized by low 87Sr/86Sr and high 143Nd/144Nd, 206Pb/204Pb, and 3He/4He ratios. This new isotopic component may be the lower mantle, entrained into plumes originating from the core-mantle boundary layer.

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