仙台市西方,安達火山噴出物のストロンチウム同位体比

抄録

The Adachi volcano situated to the west of Sendai, Northeast Japan is assumed to be thesource of the Adachi-Medeshima pumice belonging to the Late Pleistocene. Strontium isotoperatios of four samples of the products of the Adachi volcano were determined. The determinedrocks are 1) fresh and white pumice (cummingtonite dacite), 2) cummingtonite dacite (lithicfragment), 3) leucocratic cummingtonite tonalite (lithic fragment), 4) hornblende bearing cummingtonite tonalite (lithic fragment). ⁸⁷Sr/⁸⁶Sr ratios of all the rocks fall within a narrow rangebetween 0.70435 and 0.70447. The results obtained in the present study support an assumption thatthese rocks are co-genetic in origin.