www.earth2class.orgk12w6_s2005E2Cfeb05core.ppt by dffhrtcv3

VIEWS: 0 PAGES: 24

									     Dave Walker   Lamont-Doherty Earth Observatory, Columbia U.

What are some big issues in geochemistry?
                                                      Mantle to
Mantle – Crust                                       Core transfer!
  transfer!

                                     Liquid
                                            metal       Crust
                                      Core M Rocky
                                            antle



        But what about Core to Mantle transfer?
                   12 February 2005, Earth2Class@LDEO
“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?
      187
           Re -          Os ®
                       187         187/188
                                             Os
                             gOs
    190
          Pt -     Os ® 186/188Os
                 186
                                              eOs

        for gOs- eOs correlation
                  need
           DOs > DRe >> DPt
   DOs/Re ~1.2-1.4      DOs/Pt ~3-10 this!
Inner core crystallization would do
Some plume basalts do show
  correlated Os anomalies.




     Brandon, Walker et al. (2003)
          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
                  Cooling DT drives solubility changes.
                   Braginsky, Stevenson, Walker etc.
Lower Mantle

                          Ito et al. (1995)

                       Plastic solid t~109 yr



                                                          [Buffett et al.
                                      Fluid metal           substitute
                                        t~102 yr          oxide crystals
               Exsolutive
 Core




                                                            for liquid
                cooling                                       blobs]
          1 atmosphere               ?? 1 megabar ??

     Liquid                         Liquid


     L        Liquid +               L           Liquid +
T   +Fe        oxide          T     +Fe           oxide


     Fe + FeO                        Fe + FeO


Fe        0.2% oxygen    oxide Fe     ?? ~20% oxygen   oxide
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.
http://xraysweb.lbl.gov/bl1222/home.htm
                     Experiments at ALS/LBL
                     With Mike Walter*, Simon
                        Clark, Martin Kunz,
                          and many others



                                  *
                                  X-rays
                                    in



                         X-rays
                           in

LBL ALS Station 12.2.2
  X-ray density for chemical analysis!




                         Fe

                              FeO

                   Steel gasket
In situ DAC X-Radiographic Imaging (XRI)
              Laser
             melting


Fe   FeO
            Transmission
           imaging in situ
                         FeO

Itrans         Liquid          %O2
         Fe


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




           Peritectic
           possible                     FeO
         to recognize              Fe
50 kilobars




Fe
     FeS




              Melting shows erosion
550 kilobars




   FeO

               Fe

                    No erosion on melting!
          1 atmosphere               ?? 1 megabar ??




                                               T
     Liquid                         Liquid



T
     L
    +Fe


     Fe + FeO
              Liquid +
               oxide          T


                                    N
                                     L
                                    +Fe


                                     Fe + FeO
                                             O   Liquid +
                                                  oxide




Fe        0.2% oxygen    oxide Fe     ?? ~20% oxygen   oxide
    Oxygen solubility does not appear to be
        high enough to be interesting.

                                      Lumpy D′′
                                     probably not
                                       exsolved,
                                     floating slag
                                     on molten Fe
                                      of the outer
                                          core

Are there other solutions to the problem?
   What does the presence of life do for us?
 N2 + O2




 D” includes
CMB magma
                   Oxidized crust
                Oxidative titration of core®mantle
  chambers
            Contaminated plume source
  Core signal generated by recycled oxidized crust.
          1 megabar                    ?? 1 megabar ??

                                      High
                                   Liquid solubility


                                                 T
     Liquid
                                 FeO(liquid) ↔ FeO(solid)



                                               O
                                       Upon cooling
     L      Liquid +                   L            Liquid +




                                      N
T   +Fe      oxide Oxidizing     T    +Fe            oxide
                                         Low solubility
                     titration
                                     Fe(liquid) + O(reflux)
     Fe + FeO                             + FeO
                                       Fe = FeO(solid)
                                     Like a titration reaction
Fe    ? ~2% oxygen        oxide Fe       ?? ~20% oxygen   oxide
Remaining questions:
 Is the core really leaking?
 What are crustal digestion
  processes at the CMB?
Does the biosphere corrode
         the core?
    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.
Do the melting relations work?




                  Morse (2000)

                      Guess what, we have no idea!
   Two in situ properties needed to
characterize ternary liquid composition.

   Pvsk
          FeO
 Fe

								
To top