東北日本の低温高圧型変成岩類

母体-松ケ平帯

抄録

High P/T metamorphic rocks are distributed at the Kuzumaki, Motai, Yamagami, Matsugadaira and Yaguki areas in Northeast Japan. The Kuzumaki rnetamorphics are located on the Kuzumaki tectonic line. The other rnetamorphics are the constituents of the Motai-Matsugadaira tectonic zone. The zone is considered to have been the suture zone, along which the South Kitakami-East Abukuma allochthonous block collided. Mineral assemblages and compositions suggest that the metamorphic rocks of the Motai, Matsugadaira and Yaguki areas belong to epidote-glaucophane schist subfacies, and have been probably the products of a once extended high P/T metamorphism (Motai-Matsugadaira metamorphism). The Yamagami metamorphics belong to epidote-amphibolite facies. The representative mineral assemblages of the Yamagami mafic metamorphics are barroisite+epidote+chlorite+garnet+albite±quartz. Because barroisites are partly replaced by finegrained magnesioriebeckite, actinolite and green biotite, which are typical in the Matsugadaira area, the Yamagami metamorphics may have been affected secondarily by the Motai-Matsugadaira metamorphism. In the Motai-Matsugadaira zone, metamorphic rocks are best exposed at the Motai area. Amphibolite, serpentinite, gabboro and chert occur as blocks in pelitic-psammitic matrix in the area. The field evidence and metamorphic petrology suggest that the mixing occurred before the Motai-Matsugadaira metamorphism, and probably during- the deposition of metamorohic orotoliths.