1. The University of Sydney
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. Moresi et al., 2000; O’Neill et al., 2002
Numerical Models
Moresi et al., 2000; O’Neill et al., 2002

11. Numerical Models Moresi et al., 2000 O’Neill et al., 2002 H F
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. Restriction to Archean terranes too stringent
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