Methods of local analysis for study of carbon in silicates: Nuclear microprobe analysis and secondary ion mass spectrometry

Abstract

New approaches are proposed to analyze the content, distribution, and diffusion of carbon in silicates using nuclear microprobe analysis and secondary-ion mass spectrometry (SIMS). Techniques based on the nuclear reaction ¹²C(d,p)¹³C were developed to determine the coefficients of radiation-enhanced carbon diffusion in olivine at 300–370 K and deuteron doses that are comparable in terms of defect formation with those of α-particles generated by the decay of uranium and thorium isotopes for ~400 Ma (olivine age). The coefficients of thermal (D_th) and radiation-enhanced (D_rad) carbon diffusion in synthetic forsterite were compared to those of natural olivines from alkaline basalt nodule (Shevaryn Tsaram volcano, Mongolia). It is demonstrated that the diffusion coefficients strongly depends on the migration mechanisms of carbon atoms in crystals. The developed techniques and software package for SIMS determination of carbon distribution in silicates allowed us to study simultaneously the carbon and hydrogen distribution in a glass vein of the Chelyabinsk meteorite. The possible presence of hydrocarbons in the studied silicate glass of meteorite is suggested.