Permalink : http://hdl.handle.net/2115/36679

Ultramafic inclusions in volcanic rocks occur commonly in alkalic rocks. Recently we have examined some of their host rocks in Japan, and found that most of the inclusions from Oshima-Ōshima and Ichinomegata volcanoes, north Japan, occur in calc-alkalic andesite. Occurrence of such inclusions may be significant for the origin of calc-alkalic andesite which is a characteristic volcanic product in island arcs. On the basis of field petrology of Oshima-Ōshima and Ichinomegata volcanoes, two different possible processes are suggested for the genesis of the calc-alkalic andesite magmas, i.e. 1) fractional crystallization of basaltic magma, and 2) partial melting of the upper mantie, respectively.