ABSTRACT

The ⁸⁷Sr/⁸⁶Sr ratios of six representative tephrite series rocks, including 1981–1982 lavas, from Nyamuragira volcano, Western Rift have been determined. The range and average of the ratios are from 0.70543 to 0.70587 and 0.70572, and agree well with those of ugandite from the Western Rift (0.7054–0.7059 and 0.7056) reported by BELL and POWELL (1969) and POWELL and BELL (1974). Petrological and geochemical data suggest that the tephrite series, olivine basanite–tephrite–phonolitic tephrite–tephritic phonolite are products of successive fractionation of a parental ugandite magma (AOKI et al., 1984). These isotopic results support strongly this conclusion.