Diamond Crystallization at High Pressure: The Relative Efficiency of Metal-Graphite and Metal-Carbonate Systems
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Diamond Crystallization at High Pressure: The Relative Efficiency of Metal-Graphite and Metal-Carbonate Systems V. M. Sonina,*, A. A. Tomilenkoa, E. I. Zhimuleva, T. A. Bul’baka, T. Yu. Timinaa, A. I. Chepurova, and Academician N. P. Pokhilenkoa Received March 12, 2020; revised April 16, 2020; accepted April 20, 2020
Abstract—Data on the interaction of the Fe–Ni melt with CaCO3 and graphite at 5 GPa and 1400°С under the thermogradient conditions used in experiments on the growth of diamond on the BARS high-pressure apparatus are presented. The phase composition and component composition of the fluid captured by diamonds in the form of inclusions were studied by gas chromatography–mass spectrometry (GC–MS). Diamonds were synthesized from graphite. During the interaction of the Fe–Ni melt with CaCO3, Ca–Fe oxides and (Fe, Ni)3C carbide were formed. The stability of heavy hydrocarbons under the experimental conditions was confirmed. It was established that the composition of the fluid in synthesized diamonds is close to the composition of the fluid from inclusions in some natural diamonds. Nevertheless, it was concluded that crystallization of large diamonds under natural conditions is hardly possible due to the filling of the main crystallization volume with refractory oxide phases. Keywords: diamond, high pressure, high temperature, Fe–Ni melt, carbonate, fluid, hydrocarbons DOI: 10.1134/S1028334X20070181
The paper published by Wentorf and Bovenkerk in 1961 contained a hypothesis, based on experimental studies on the synthesis of diamond at high PT parameters, about the participation of metal melts in the genesis of natural diamonds [1]. Only 29 years later, the results of diamond synthesis in the presence of melts of alkaline and alkali-earth carbonates, such as Li2CO3, Na2CO3, MgCO3, CaCO3, and SrCO3, were published, where, instead of carbonate carbon, graphite was used as a carbon source [2]. Currently, there are many studies on the crystallization of diamond in graphite–carbonate systems. The hypothesis about the participation of metal melts in the genesis of natural diamonds received a new impetus in connection with detailed studies of inclusions in CLIPPIR diamonds (Cullinan-like, Large, Inclusion-Poor, Pure, Irregular, and Resorbed) [3]. It was assumed that the genesis of CLIPPIR diamonds was associated with subduction processes. Oxidized crustal material fell into the deep horizons of the Earth’s mantle, where Fe–Ni–S–C melts are stable. Carbon from carbonate phases and СО2 captured by the subducting plate was restored to elemental form, and diamond crystallization occurred in “drops” of a Sobolev
Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia *e-mail: [email protected]
the sulfonated Fe–Ni melt [3]. Diamond crystallization in the Fe(+Ni)–S system was carried out in experimental studies [4, 5]. Thus, the subduction carbonate material (originally CaCO3) could be the source of carbon in the process of diamond crystallization. The review
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