title: Episodic entrainment of deep primordial mantle material into ocean island basalts.
abstract: Chemical differences between mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs) provide critical evidence that the Earth's mantle is compositionally heterogeneous. MORBs generally exhibit a relatively low and narrow range of (3)He/(4)He ratios on a global scale, whereas OIBs display larger variability in both time and space. The primordial origin of (3)He in OIBs has motivated hypotheses that high (3)He/(4)He ratios are the product of mantle plumes sampling chemically distinct material, but do not account for lower MORB-like (3)He/(4)He ratios in OIBs, nor their observed spatial and temporal variability. Here we perform thermochemical convection calculations which show the variable (3)He/(4)He signature of OIBs can be reproduced by deep isolated mantle reservoirs of primordial material that are viscously entrained by thermal plumes. Entrainment is highly time-dependent, producing a wide range of (3)He/(4)He ratios similar to that observed in OIBs worldwide and indicate MORB-like (3)He/(4)He ratios in OIBs cannot be used to preclude deep mantle-sourced hotspots.
authors.affiliation: Department of Earth and Planetary Sciences, University of California at Davis, One Shields Avenue, Davis, California 95616, USA.|Arizona State University, School of Earth and Space Exploration, PO Box 876004, Tempe, Arizona 85287-6004, USA.
authors.forename: Curtis D
authors.initials: CD
authors.lastname: Williams
authors.affiliation: Arizona State University, School of Earth and Space Exploration, PO Box 876004, Tempe, Arizona 85287-6004, USA.
authors.forename: Mingming
authors.initials: M
authors.lastname: Li
authors.affiliation: Arizona State University, School of Earth and Space Exploration, PO Box 876004, Tempe, Arizona 85287-6004, USA.
authors.forename: Allen K
authors.initials: AK
authors.lastname: McNamara
authors.affiliation: Arizona State University, School of Earth and Space Exploration, PO Box 876004, Tempe, Arizona 85287-6004, USA.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Garnero
authors.affiliation: Arizona State University, School of Earth and Space Exploration, PO Box 876004, Tempe, Arizona 85287-6004, USA.
authors.forename: Matthijs C
authors.initials: MC
authors.lastname: van Soest