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12 February 2005, Earth2Class@LDEO

Dave Walker Lamont-Doherty Earth Observatory, Columbia U. Mantle – Crust transfer!. Mantle to Core transfer!. But what about Core to Mantle transfer?. What are some big issues in geochemistry? . Crust. Liquid metal. Rocky. Core. Mantle. 12 February 2005, Earth2Class@LDEO.

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12 February 2005, Earth2Class@LDEO

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  1. Dave Walker Lamont-Doherty Earth Observatory, Columbia U. Mantle – Crust transfer! Mantle to Core transfer! But what about Core to Mantle transfer? What are some big issues in geochemistry? Crust Liquid metal Rocky Core Mantle 12 February 2005, Earth2Class@LDEO

  2. “The core is leaking! The core is leaking!” What would be an appropriate response? • Run and find Chicken Little? • Write NSF or DOE for a grant? • Call the National Enquirer? Is the core really leaking?

  3. 187Re - 187Os 187/188OsgOs 190Pt - 186Os186/188OseOs for gOs- eOs correlation need DOs >DRe >>DPt DOs/Re ~1.2-1.4 DOs/Pt ~3-10 Inner core crystallization would do this!

  4. Some plume basalts do show correlated Os anomalies. Brandon, Walker et al. (2003)

  5. Is the core really leaking? What could drive it? Manghnani and Yagi Yes, perhaps: Os isotopes Hawaiian plume Fe/Mn No: W isotopes & radiogenic Sr/Os correlation

  6. Cooling DT drives solubility changes. Braginsky, Stevenson, Walker etc. Ito et al. (1995) Plastic solidt~109 yr Lower Mantle [Buffett et al. substitute oxide crystals for liquid blobs] Fluid metal t~102 yr Exsolutive cooling Core

  7. ?? 1 megabar ?? 1 atmosphere Liquid Liquid L +Fe Liquid + oxide L +Fe Liquid + oxide T T Fe + FeO Fe + FeO Fe oxide Fe oxide ?? ~20% oxygen 0.2% oxygen

  8. But what is the solubility of oxygen in liquid Fe? And how could it be measured at a megabar? Non-divergent synchrotron X-rays for imaging.

  9. Experiments at ALS/LBL With Mike Walter*, Simon Clark, Martin Kunz, and many others * http://xraysweb.lbl.gov/bl1222/home.htm

  10. X-rays in X-rays in LBL ALS Station 12.2.2

  11. X-ray density for chemical analysis! Fe FeO Steel gasket In situ DAC X-Radiographic Imaging (XRI)

  12. Fe FeO Laser melting Transmission imaging in situ

  13. FeO Itrans %O2 Liquid Fe Single in situ property (Itrans) to characterize binary join. Liq FeO Fe Eutectic

  14. Liquid FeO Itrans %O2 Fe FeO Fe Peritectic possible to recognize

  15. Melting shows erosion 50 kilobars Fe FeS

  16. No erosion on melting! 550 kilobars FeO Fe

  17. ?? 1 megabar ?? 1 atmosphere Liquid Liquid L +Fe Liquid + oxide L +Fe Liquid + oxide T T Fe + FeO Fe + FeO Fe oxide Fe oxide ?? ~20% oxygen 0.2% oxygen NOT

  18. Lumpy D′′ probably not exsolved, floating slag on molten Fe of the outer core Oxygen solubility does not appear to be high enough to be interesting. Are there other solutions to the problem?

  19. N2+O2 Oxidized crust D” includes CMB magma chambers Contaminated plume source Oxidative titration of coremantle What does the presence of life do for us? Core signal generated by recycled oxidized crust.

  20. ?? 1 megabar ?? 1 megabar Liquid Liquid NOT L +Fe Liquid + oxide L +Fe Liquid + oxide T T Oxidizing titration Fe + FeO Fe + FeO Fe oxide Fe oxide ?? ~20% oxygen ? ~2% oxygen High solubility FeO(liquid) ↔ FeO(solid) Upon cooling Low solubility Fe(liquid) + O(reflux) = FeO(solid) Like a titration reaction

  21. Remaining questions: Is the core really leaking? What are crustal digestion processes at the CMB? Does the biosphere corrode the core?

  22. Activities/questions • Would you expect gravitational acceleration to vary as you go from crust to core? • It doesn’t vary much. Why not? • What is average density of the mantle if pressure at the CMB is 1.3 megabar? • How much force must a DAC use to hit a megabar? • Give an example of exsolution with a pressure change or with a temperature change. [See E2C from October 2002.] • Give an example of a precipitation or titration reaction.

  23. Do the melting relations work? Morse (2000) Guess what, we have no idea!

  24. Two in situ properties needed to characterize ternary liquid composition. Pvsk FeO Fe

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