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首页> 外文期刊>Contributions to Mineralogy and Petrology >Diamond formation in the system MgO–SiO2–H2O–C at 7.5 GPa and 1,600°C
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Diamond formation in the system MgO–SiO2–H2O–C at 7.5 GPa and 1,600°C

机译：在7.5 GPa和1,600°C下MgO–SiO 2 –H 2 O–C系统中的金刚石形成

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摘要

Diamond crystallization has been studied in the SiO2–H2O–С, Mg2SiO4–H2O–С and H2O–С subsystems at 7.5 GPa and 1,600°C. We found that dissolution of initial graphite is followed by spontaneous nucleation of diamond and growth of diamond on seed crystals. In 15-h runs, the degree of graphite to diamond transformation [α = MDm/(MDm + MGr)100, where MDm is mass of obtained diamond and MGr mass of residual graphite] reached 100% in H2O-rich fluids but was only 35–50% in water-saturated silicate melts. In 40-h runs, an abrupt decrease of α has been established at the weight ratio H2O/(H2O + SiO2) ≤ 0.16 or H2O/(H2O + Mg2SiO4) ≤ 0.15. Our results indicate that α is a function of the concentration of water, which controls both the kinetics of diamond nucleation and the intensity of carbon mass transfer in the systems. The most favorable conditions for diamond crystallization in the mantle silicate environment at reliable PT-parameters occur in the fluid phase with low concentration of silicates solute. In H2O-poor silicate melts diamond formation is questionable.
机译：在SiO 2 –H 2 O–С，Mg 2 SiO 4 –H中研究了金刚石的结晶 2 O–С和H 2 O–С子系统的温度为7.5 GPa和1,600°C。我们发现，初始石墨溶解后，金刚石会自发成核并在晶种上生长。在15小时的运行中，石墨到金刚石的转化度[α= M Dm /（M Dm + M Gr ）100，其中M Dm 是所得钻石的质量，而M Gr 残余石墨的质量]在富含H 2 O的流体中达到100％，但仅为35 –50％的水饱和硅酸盐熔体中。在40小时的运行中，在重量比H 2 O /（H 2 O + SiO 2 ）≤0.16或H 2 O /（H 2 O + Mg 2 SiO 4 ）≤0.15。我们的结果表明，α是水浓度的函数，水浓度既控制金刚石成核的动力学，又控制系统中碳质量转移的强度。在可靠的PT参数下，在地幔硅酸盐环境中金刚石结晶的最有利条件发生在液相中硅酸盐溶质浓度低的情况下。在H 2 O贫硅酸盐熔体中，金刚石的形成值得怀疑。

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