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Pb isotopic variability in melt inclusions from the EMI–EMII–HIMU mantle end-members and the role of the oceanic lithosphere |
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| Authors: | AE Saal SR Hart N Shimizu EH Hauri GD Layne and JM Eiler |
| Institution: | aDepartment of Geological Sciences, Brown University, 324 Brook Street, Box 1846, Providence, Rhode Island 02912, United States bDepartment of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, United States cDepartment of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, District of Columbia 20015, United States dDivision of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, United States |
| Abstract: | Melt inclusions from four individual lava samples representing the HIMU (Mangaia Island), EMI (Pitcairn Island) and EMII (Tahaa Island) end member components, have heterogeneous Pb isotopic composition larger than that defined by the erupted lavas in each island. The broad linear trend in 207Pb/206Pb–208Pb/206Pb space produced by the melt inclusions from Mangaia, Tahaa and fPitcairn samples reproduces the entire trend defined by the Austral chain, the Society islands and the Pitcairn island and seamount groups. The inclusions preserve a record of melt composition of far greater isotopic diversity than that sampled in whole rock basalts. These results can be explained by mixing of a common depleted component with the HIMU, EMI and EMII lavas, respectively. We favor a model that considers the oceanic lithosphere to be that common component. We suggest that the Pb isotopic compositions of the melt inclusions reflect wall rock reaction of HIMU, EMI and EMII melts during their percolation through the oceanic lithosphere. Under these conditions, the localized rapid crystallization of olivine from primitive basalt near the reaction zone would allow the entrapment of melt inclusions with different isotopic composition. |
| Keywords: | melt inclusions Pb isotopes oceanic island basalts |
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