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Diffusion in diamond. II. High-pressure-temperature experiments

¹ School of GeoSciences, University of Edinburgh, Edinburgh EH9 3JW, UK
² National Institute for Materials Sciences, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
³ Institute of Geology, Mineralogy and Geophysics, Ruhr-Universität Bochum, D-44780 Bochum, Germany

^* E-mail: B.Harte{at}ed.ac.uk

ABSTRACT

High-pressure-temperature (P-T) experiments were conducted in an attempt to determine the diffusion rates of C atoms in diamond, and the possibility of changes in the isotope compositions of diamond at high P-T in the Earth's mantle. The starting material consisted of a polished plate of natural diamond (very largely ¹²C), which had been coated with ¹³C diamond by chemical-vapour deposition to form a sharp interface between ¹²C and ¹³C diamond. Three experiments were performed at 1800, 2000 and 2300°C, all at 7.7 GPa, for 0.5-20 h. Isotopic profiles obtained by ion microprobe before and after each experiment showed no evidence of relaxation of the sharp interface between ¹²C and ¹³C, and so diffusion must have been on a scale less than the 32 nm depth resolution for this technique. Using 32 nm as the maximum length scale of diffusion across the interface, the maximum ln D (diffusion coefficient) values for the experiments were calculated to be in the range -38 to -42. Unlike previous experimental data, these results show that changes in the isotopic compositions of diamond on long time scales in the Earth's upper mantle are unlikely. Furthermore, the results support empirical evidence from mapping of C isotope distributions in natural diamonds that C isotope compositions reflect diamond growth compositions.

KEYWORDS: diamonds, diffusion coefficents, high-P-T experiments, Earth's mantle

This article has been cited by other articles:

				J. A. Craven, B. Harte, D. Fisher, and D. J. Schulze Diffusion in diamond. I. Carbon isotope mapping of natural diamond Mineralogical Magazine, August 4, 2009; 73(2): 193 - 200. [Abstract] [Full Text] [PDF]