# If the mantle has lower u03ba than the bulk Earth.docx -...

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. If the mantle has lower κ than the bulk Earth, then it stands to reason that the crust should have a high value than the bulk Earth. Furthermore, crustal rocks tend to have higher 208 Pb*/ 206 Pb*, suggesting κ has been lower in the mantle than in the crust for geologically long times. Paul et al. (2003) used Asmeron and Jacobsen’s (1993) estimate of the Pb composition of the riverine flux to estimate the Pb isotopic composition of upper crust and data from Rudnick and Goldstein Figure 16.8. Pb isotope ratios in lower crustal xenoliths. Eifel is in Germany; GVF (Geronimo Volcanic Field), Kilbourne Hole and Camp Creek in the southwest US, McBride in Australia; and the Massif Central, in France. From Rudnick and Goldstein (1990).
Figure 16.9. Estimates of the Pb isotopic composition of the crust: N: Newsom et al. (1986), D: Davies (1984), Z: Zartman and Doe (1981), R: Rudnick and Goldstein (1990). (1990) to estimate the Pb isotope composition the lower crust. From this they calculated a κ Pb for the crust of 4.26-4.30. This clearly implies the κ value of the crust must be higher than that estimated by
Figure 16.10.