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HSDP Drill Site

HSDP Drill Site. HSDP - a detailed look at the Hawaiian plume (and CMB?). (Sharp et al., 2004). center. Melting region. edge. Sampling issues: Pt. 1. EPR MORB range. r = 30 km. r = 130 km. MORB. MORB. The isotopic stratigraphy at the base of the mantle is not simple. Sr. He.

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HSDP Drill Site

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  1. HSDP Drill Site HSDP - a detailed look at the Hawaiian plume (and CMB?)

  2. (Sharp et al., 2004)

  3. center Melting region edge Sampling issues: Pt. 1 EPR MORB range

  4. r = 30 km r = 130 km

  5. MORB MORB

  6. The isotopic stratigraphy at the base of the mantle is not simple Sr He

  7. Jellinek & Manga (2002) The isotopic stratigraphy at the base of the mantle is not simple Sr He

  8. 186Os data also interpreted as entrained outer core material; correlates w/ 3He Brandon et al. (1999)

  9. Re, Os, Pt and core-mantle interaction? Observations: high values of 186Os/188Os and 187Os/188Os in Hawaiian lavas, Siberian lavas, and Os-rich alloys Hypothesis: Entrainment of ~1 wt% outer core material in plume Depends on: Inner core-outer core partition coefficients for Re, Os, Pt crust mantle Outer core Re Os Pt Inner core (R. Walker et al. 1997; Brandon et al. 1998; Meibom & Frei 2002)

  10. crust high 187Os/188Os high Re/Os Re Os Pt mantle high 187Os/188Os Outer core high 186Os/188Os high Re/Os Inner core Re Os Pt high Pt/Os outer core = only reservoir with high 187Os/188Os and 186Os/188Os Std gchems story Re, Os, Pt systematics 187Re  187Os 190Pt  186Os (Brandon et al. 1998; Shen et al.1996; D.Walker 2000)

  11. Mauna Loa data suggest that core of plume is longitudinally heterogeneous

  12. Recent deviant lavas from Mauna Loa require longitudinal heterogeneity along the axis of the plume

  13. The axial part of the plume is longitudinally heterogeneous; The inner fringe of the plume is less heterogeneous The outer fringe is invisible (no melting)

  14. Conclusions • Different isotopic anomalies are not spatially correlated in the lowermost mantle • The 3He anomaly is not a general feature of the “lower mantle” but is a feature of the base of the mantle • Most of the mantle between the plume source and the surface could have R/Ra ≈ 8; however, there are no lavas to represent this entrained material • The Sr isotope anomaly (87Sr/86Sr ≈ 0.70365) at Hawaii is a broad feature and the isotopic composition could represent a large volume of the lower mantle under Hawaii • Patterns for Hf, Nd, Os resemble Sr; but 208Pb resembles 3He • Juxtaposing isotopic data with physical models can yield new perspectives

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