火山噴出物と同位体の研究

抄録

Volcanic emanations have been studied with respect to H, He, B, C, N, O, S and Ar isotopes. This paper deals with studies on H, C, O and S isotopes which have proved their usefulness in the field of chemical volcanology. 1. Carbon isotopic exchange equilibrium between methane and carbon dioxide enables to calculate an equilibrium temperature deep underground. 2. δC¹³ values of total carbon from volcanic areas fall in the narrow range 0～-5%, suggesting a significant contribution of limestone carbon dioxide to volcanic gases. 3. δS³⁴ values for volcanic sulfur compounds are explained by sulfur isotopic exchange equilibria among them. 4. δS³⁴ values for total sulfur discharged from volcanic areas seem to approach to the meteoritic troilite value. 5. Waters from volcanic areas can not be distinguished from surface waters in terms of hydrogen isotopes, except that some of them are marked with high O¹⁸ values, which are close to silicate oxygen values of igneous rocks. Magmatic water can be distinguished by O¹⁸ concentration. This, however, can not tell whether it is vadose or juvenile in origin.