Lawrence's fields of expertise are in all forms of petrology (igneous, sedimentary, metamorphic), geochemistry, thermodynamics, statistics, and database control of large petrology collections. He has done extensive petrological research into Alaskan complexes (platinum), subduction diamonds, Raman and FTIR spectroscopy of diamonds, and has produced metamorphic maps of 1:250 000 standard map sheets. Lawrence Murray Barron - barronjandl@optusnet.com.au Resume Publication list Biography
RESEARCH ON NEW SOUTH WALES DIAMONDS
Jane and Larry's research on NSW diamonds has publications appearing (2008). Please email barronjandl@optusnet.com.au for more information.
A recent publication that uses previously determined remnant pressures on inclusions to calculate entrapment PT loci which intersect, and hence constrain the Copeton diamond formation conditions is as follows (Abstract):
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Mining of Cenozoic alluvial deposits at Copeton and Bingara (Eastern Australia) has produced two million macrodiamonds (0.25 ct median size). Raman spectroscopy is used to identify included minerals within uncut Copeton diamonds, with sealed chamber remnant pressures of 31.7 to 35.6 kbar for coesite, 13.6 and 22.7 kbar for clinopyroxene, and 7.6 kbar for grossular garnet. Assuming elastic behaviour, these values generate inclusion entrapment PT loci which intersect, restricting diamond formation conditions: from 250 °C, 43 kbar to 800 °C, 52 kbar. Larger than error (±100 °C and ±4 kbar), this range shows a systematic variation in inclusion composition with diamond zoning and N properties. Published research shows 1) Copeton and Bingara diamonds are unique, and 2) modern alluvium in the Bingara district carries mantleformed garnet, captured by post-tectonic alkali basalt from an extensive diamondiferous ultrahigh pressure (UHP) terrane that stalled at depth because it is dominated by mafic eclogite. The combined Raman and geological results indicate two sets of subduction UHP diamond formation conditions/protolith are required, firstly cooler oceanic slab and secondly including higher temperature continental crust. The Copeton and Bingara stones are UHP macrodiamonds, and Carboniferous 40Ar/39Ar age dates on clinopyroxene inclusions should be interpreted as ages of crystallisation, representing the termination of subduction. The characteristic features of ruptured inclusions and etched percussion marks on Copeton and Bingara diamond indicate volcanic delivery to the earth's surface. Alluvial deposits elsewhere in Eastern Australia may carry similar diamond along with diamond of different origin.
[ Ultrahigh pressure macro diamonds from Copeton (New South Wales, Australia), based on Raman spectroscopy of inclusions. By L.M. Barron, B.J. Barron, T.P. Mernagh and W.D. Birch. Ore Geology Reviews 34 (2008) 76–86. ]
[ Corresponding author's present address: Australian Museum, 6 College St, Sydney, NSW 2010, Australia. Tel./fax: +61 2 94495839. E-mail address: barronjandl@optusnet.com.au (L.M. Barron). ]
To view corresponding author's copy of the entire article, for private study only - see via this link: Barron-etc-diamond08.pdf
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The below figure (click on the full PDF link below it to get a larger file) pertains to NSW diamond research published in Australian Journal of Earth Science(Barron et al 2008). It shows the graph for determining the internal pressure (Pr) on an inclusion in diamond from the maximum strain birefringence in the diamond adjacent to the inclusion - a geobarometer in every petrological microscope, taking only a few seconds to use.
There are photo-examples of inclusions surrounded by strain birefringence haloes, so the user can try the technique. A key point about the technique is that high birefringence orders can be simply counted (like birefringence orders in a uniaxial cross), see the top right image of a near spherical coesite inclusion embedded in top second order strain birefringence with the inclusion under about 35 kbar Pr.
DOWNLOAD LARGER FILE:
Click the link at right to view the PDF; or right mouse click to download it ===> PrBireCHARTa4.pdf
