High-pressure experimental growth of diamond using C-K2CO3-KCl as an analogue for Cl-bearing carbonate fluid

Emma Tomlinson, Adrian P. Jones, Judith Milledge

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High-pressure, high-temperature diamond growth experiments have been conducted in the system C-K2CO3-KCl at 1050-1420degreesC, 7.0-7.7 GPa. KCl is of interest because of the strong effect of halogens on the phase relations of carbonate-rich systems [Geophys. Res. Lett. 30 (2003) 1022] and because of the occurrence of KCl coexisting with alkali silicate-carbonate fluids in natural-coated diamond [Geochim. Cosmochim. Acta 64 (2000) 717]. We have used system C-K2CO3-KCl as an analogue for these mantle fluids in diamond growth experiments. The presence of KCl reduces the potassium carbonate liquidus to < 1000degreesC at 7.7 GPa, allowing it to act as a solvent catalyst for diamond growth at temperatures below the continental geotherm. This is a reduction on the minimum diamond growth temperature reported in the alkali-carbonate-C-O-H system [Lithos 60 (2002) 145]. Diamond growth using carbonate solvent catalysts is characterised by a relatively long induction period. However, the addition of KCl also reduced the period for diamond growth in carbonate to much less than 5 min; no such induction period appears to be necessary. It is suggested that KCl destabilises carbonate, allowing greater solubility and diffusion of carbon.
Original languageEnglish
Pages (from-to)287-294
Issue number1-4
Publication statusPublished - Sept 2004

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