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Trace elements

This document explores the intricacies of partition coefficients (Kd) and selective affinities of elements like Fe2+, Mg2+, Ni2+, and Au3+ in geological contexts. It contrasts compatible and incompatible elements regarding mineral compositions, particularly focusing on lherzolites and cumulates. The impact of specific minerals on elemental concentrations and the evolution of residual liquids is studied, alongside normalization methods relative to CHON and MORB patterns. The significance of rare earth elements (REEs) and anomalies such as Eu in various rock types is also addressed, providing a comprehensive overview for geoscientists.

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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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