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Magnesian andesite and basalt from Shodo-Shima Island, southwest Japan, and their bearing on the genesis of calc-alkaline andesites

1982; Elsevier BV; Volume: 15; Issue: 2 Linguagem: Inglês

10.1016/0024-4937(82)90007-x

1872-6143

Yoshiyuki Tatsumi, Kyoichi Ishizaka,

earthquake and tectonic studies

Calc-alkaline andesites and olivine tholeiitic basalts are widely distributed on Shodo-Shima island, southwest Japan. The Fo content of olivine phenocrysts in the andesite is higher than in the basalt. The primary magma of the andesite, estimated on the basis of the olivine fractional crystallization model, is not basaltic but andesitic. The basalt contains both chromite and titanomagnetite as inclusions in olivine phenocrysts, while only chromite appears in the andesite. The Cr content of chromite in the andesite is higher than in the basalt. These facts again indicate that the andesite cannot be a fractionation product of the basalt, and that andesitic and basaltic primary magmas were generated independently.