Synthesis and diffusion measurement of double-layered single crystals of olivine

Abstract

Double-layered single crystals of olivine, (Mg, Ni)₂SiO₄-and (Mg, Co)₂SiO₄-Mg₂SiO₄, were synthesized for the purpose of measuring cation inter-diffusivities in olivine. The olivine solid solution layers were epitaxially overgrown on the surface of forsterite seed crystals in Li₂O-MoO₃-V₂O₅ flux systems at temperatures below, 1,000℃. Diffusion annealing was performed at 1,050〜1,450℃ for 5 hours to 81 days. Diffusion coefficients observed showed relations D=D₀exp (-E_D/kT), where D₀ for Co-Mg and Ni-Mg are 68.6 and 15.1 cm²/sec, respectively and E_D for both Co-Mg and Ni-Mg are 407 kJ/mol. The observed D's are nearly an order of magnitude lower than those previously observed by Morioka (1980;1981), although E_D's agree with the previous values. The observed discrepanceies in D's were discussed in terms of diffusion mechanism.