Geodynamics of diamond deposits Craig O’Neill The University of Sydney
Dec 20, 2015
Geodynamics of diamond deposits
Craig O’NeillThe University of Sydney
New Scientist, 21st September 2002
Formation of diamond deposits: the standard model
Helmstaedt and Gurney, 1995
Southern Africa
Shirey et al. 2002
Southern African geotherms
On-craton
Off-craton
Graphite
Diamond
Clifford’s Rule
Helmstaedt and Gurney, 1995
AustraliaArgyle: Lamproite
Hall’s Creek mobile belt (Proterozoic), adjacent to Kimberley block (possible Archean basement)
Australia’s diamond occurrences
Merlin: Kimberlite
Central Australian mobile belts
Structure of the Australian Lithosphere
Cross-sections
Numerical Models
Moresi et al., 2000; O’Neill et al., 2002
Numerical Models
Moresi et al., 2000O’Neill et al., 2002
Time in DSF
On-craton
Off-craton
H F
Percentage timegeotherms spend in
DSF
A. Distance to COB B. Archean cratons
C. Distance from cratons D. Combined
Tomographycross-sectionsthrough Argyle
and Merlin
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