Mantle Plumes and Entrainment: Isotopic Evidence

• Published in: Science (American Association for the Advancement of Science) Vol. 256; no. 5056; pp. 517 - 520
• Main Authors: Hart, S. R., Hauri, E. H., Oschmann, L. A., Whitehead, J. A.
• Format: Journal Article
• Language: English
• Published: United States American Society for the Advancement of Science 24-04-1992; American Association for the Advancement of Science; The American Association for the Advancement of Science
• Subjects: Basalt; Chemistry; Datasets; Earth; Geology; Islands; Isotope geology; Lower mantle; Mantle; Mantle (Geology); Oceanic islands; Organic Chemistry; Plumes; Sampling; Statistical variance; Tetrahedrons; Upper mantle; Volcanism
• ISSN: 0036-8075; 1095-9203
• 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 $^{87}$Sr/$^{86}$Sr and high $^{143}$Nd/$^{144}$Nd, $^{206}$Pb/$^{204}$Pb, and $^3$He/$^4$He ratios. This new isotopic component may be the lower mantle, entrained into plumes originating from the core-mantle boundary layer.