title: Mantle plumes and entrainment: isotopic evidence.
abstract: 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.
authors.forename: S R
authors.initials: SR
authors.lastname: Hart
authors.forename: E H
authors.initials: EH
authors.lastname: Hauri
authors.forename: L A
authors.initials: LA
authors.lastname: Oschmann
authors.forename: J A
authors.initials: JA
authors.lastname: Whitehead