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