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Trace elements

Trace elements. Substitutions and partition coefficients Normalization and spidergrams. Fe 2+. Mg 2+. Compatible (right size & charge). Ni 2+. Au 3+. Incompatible (size/charge does not match). Ag 3+. Fe 2+. Mg 2+. Selective affinities. Partition coefficient Kd = C s /C l

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Trace elements

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  1. Trace elements

  2. Substitutions and partition coefficients • Normalization and spidergrams

  3. Fe2+ Mg2+ Compatible (right size & charge) Ni2+ Au3+ Incompatible (size/charge does not match) Ag3+ Fe2+ Mg2+ Selective affinities

  4. Partition coefficient Kd = Cs/Cl • Compatible, incompatible (relative to a mineral) • Bulk repartition coefficient D = S Kdi Xi

  5. Compatibility depends on minerals and melts involved. Which are incompatible? Why?

  6. Calculate DYb for… • A lherzolite (80% Ol, 10% Opx, 10%Cpx) • A Grt-bearing Lherzolite (70% Ol, 10% Opx-Cpx-Gt) • Calculate DSr for… • A Cpx-Plag cumulate (50/50) • A Cpx-Opx cumulate (50/50) • How will the residual liquid evolve?

  7. Fingerprinting specific minerals: • Ni strongly fractionated olivine > pyroxene • Cr and Scpyroxenes » olivine • Ni/Cr or Ni/Sc can distinguish the effects of olivine and augite in a partial melt or a suite of rocks produced by fractional crystallization

  8. Concentration of REE in a sample

  9. Chondrites

  10. Contrasted REE patterns Granites Basalts

  11. Multi-elements diagrams Normalized to the PRImitive Mantle (close to chondrites) (Wood version)

  12. Various normalizations: To MORB (Mid-Oceanic Ridge Basalts – the most common type of basalt!) Meaningful for basalts and co.

  13. Various normalizations: To the average continental crust. Meaningful for granites, sediments, etc.

  14. A famous “anomaly”: Eu Granites from the Cape Granite Suite Darling-Vredenburg area

  15. Kd’s for plagioclase • REEs are normally 3+ (La3+, etc.) • Eu can be Eu3+ or Eu2+ • Eu2+ strongly compatible Reducing (Eu2+) Oxydizing (Eu3+)

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