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Geodynamics of diamond deposits

Geodynamics of diamond deposits. Craig O’Neill The University of Sydney. New Scientist, 21 st September 2002. Formation of diamond deposits: the standard model. Helmstaedt and Gurney, 1995. Southern Africa. Shirey et al. 2002. Southern African geotherms. Graphite. Diamond.

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Geodynamics of diamond deposits

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  1. Geodynamics of diamond deposits Craig O’Neill The University of Sydney

  2. New Scientist, 21st September 2002

  3. Formation of diamond deposits: the standard model Helmstaedt and Gurney, 1995

  4. Southern Africa Shirey et al. 2002

  5. Southern African geotherms Graphite Diamond Off-craton On-craton

  6. Clifford’s Rule Helmstaedt and Gurney, 1995

  7. Australia Argyle: Lamproite Hall’s Creek mobile belt (Proterozoic), adjacent to Kimberley block (possible Archean basement) Merlin: Kimberlite Central Australian mobile belts Australia’s diamond occurrences

  8. Structure of the Australian Lithosphere

  9. Cross-sections

  10. Numerical Models Moresi et al., 2000; O’Neill et al., 2002

  11. Numerical Models Moresi et al., 2000 O’Neill et al., 2002 Off-craton On-craton H F Time in DSF

  12. Percentage time geotherms spend in DSF

  13. Distance to COB B. Archean cratons • C. Distance from cratons D. Combined

  14. Tomography cross-sections through Argyle and Merlin

  15. Conclusions • Restriction to Archean terranes too stringent • diamond formation may not always be related to formation of cratonic roots • require PT conditions and C source • Inclusion of many stable Proterozoic platforms • Focus on where kimberlite volcanism is likely to occur • Australia example: step changes in lithospheric thicknesses could be important

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