What is the origin of OIB?

1. What is the origin of OIB? John Caulfield • Identification and explanation of similarities and differences in isotopic ratios (Sr, Nd, Os, O and Pb) between OIB and MORB, Mantle and Continental Crust. • Hence, which mantle components are unique to OIB, and which heterogeneities are the result of localised OIB interaction with crust and mantle.

2. Sr-Nd Isotope correlations SCLM xenolith Os concs. DEPLETED MORB SCLM OIB ENRICHED Modified from Hofmann 1997. Pearson et al. 1995

3. Element compatibility plot Greater enrichment in incompatible elements suggests OIB are smaller degree melts than MORB. Plume emplacement required for OIB? OIB has Nb and Pb anomalies with the same sense as MORB, and opposite to those of C.C. excludes simple two component mixing. Modified from Hofmann 1997.

4. Multi-Component mixing 1 OIB’s can be distinguished by their enrichment in three mantle components, EM1, EM2 and HIMU all of which can show elevated 187Os/188Os – suggestive of a common source. All mixing arrays converge on depleted FOZO component that is distinct from the DMM component in terms of Pb concentration. Van Keken et al. 2002

5. Multi-component mixing 2 Elevated 3He/4He of FOZO indicates primitive nature All arrays contain FOZO, but not EM1, EM2 and HIMU all together. OIB source model must reconcile supply of EM/HIMU components in differing proportions and subsequent mixing with FOZO. Van Keken et al. 2002

6. Recycling of subducted oceanic crust Subducted slab provides source for three enriched mantle components and allows for elevated 187Os/188Os. HIMU- Recycled oceanic crust EM1- Oceanic lithosphere EM2- Modern sediments 187Os/188Os correlates with δ18O. δ18O δ18O Lassiter and Hauri 1998

7. Koolau=subducted oceanic crust component and modern sediments Kea=recycled oceanic lithosphere Koolau and Kea Components Lassiter and Hauri 1997 Koolau displays elevated 3He consistent with entrainment of FOZO above D”

8. Preservation of Heterogeneity Metabasaltic lithosphere transforms to Eclogite at approx. 100km depth. Increased viscosity of Eclogite(Garnet+Cpx) preserves slab heterogeneity. High Sm/Yb ratios in Hawaiian lavas reflect the presence of Garnet in their source, precluding generation of melts in the upper lithospheric mantle. Lassiter and Hauri 1997.

9. Class and Goldstein 1997. OIB Diversity Lavas of the Honolulu series formed in the presence of residual amphibole ± phlogopite Both phases are temperature sensitive and cannot have a plume origin. These lavas are best accounted for by the mixing of an upwelling plume with oceanic lithospheric mantle.

10. Review • OIB are the product of mixing of enriched mantle components and lower mantle depleted FOZO. • Recycling of subducted slab is supported as it accounts for correlations between Os and O. • Localised OIB heterogeneity can be accounted for by mixing of the plume source with upper mantle components.

11. References Class, C., Goldstein, S.L. Plume lithosphere interactions in the ocean basins: constraints from the source mineralogy. Earth and Planetary Sci. Lett. 150 (1997) 245-260. Garcia, M.O., Ito, E., Eiler, J.M., Pietruszka. Cruatal contamination of Kilauea Volcano magmas revealed by oxygen Isotope analyses of Glass and Olivine from Puu Oo eruption Lavas. Journal of Petrology 1998 vol. 39 no.5 p.803-817. Hofmann, A.W. Mantle Geochemistry: the message from oceanic volcanism. Nature vol. 385 (1997) p.219-229. Lassiter, J.C., Hauri, E.H. Osmium-isotope variations in Hawaiian lavas: evidence for recycled oceanic lithosphere in the Hawaiian plume. Earth and Planetary Sci. Lett. 164 (1998) p.483-496 Pearson, D.G., R.W. Carlson, R.W., Shirley S.B., Boyd, F.R., Nixon P.H. Stabilisation of Archean Lithospheric mantle: A Re-Os study of peridotite xenoliths from the Kaapvaal Craton. Earth and Planetary Sci. Lett. 134. (1995) p.341-357 Van Keken, P.E., Hauri, E.H., Ballentine, C.J. Mantle Mixing: The generation, preservation, and destruction of chemical heterogeneity. Annu. Rev. Earth Planet. Sci. (2002), 30 p.493-525.