Sr isotope study of the tephrite series from nyamuragira volcano, zaire

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 xell with those of ugandite from the Western Rift (0.7054-0.7059 and 0.7056) reported by BELLa nd POWELL(1969) and POWELLan d 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. © 1984, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.