Geological and petrological studies of low-temperature metamorphic rocks in the northern Kitakami Mountains.

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The northern part of the Kitakami Mountains is composed mainly of late Paleozoic to late Mesozoic sedimentary rocks, which were mostly subjected to contact metamorphism by Cretaceous granitic intrusions. However, low-temperature regional metamorphic rocks have been found in separate fragmental areas unaffected by the later contact metamorphism.The typical low-temperature metamorphic remnants, the Kuzakai, Morioka, Manami-yamagata and Kuzumaki areas, in the "Hayachine Tectonic Belt" and North Kitakami Belt were studied in detal. In these areas the pumpellyite + actinolite association is commonly found in mafic rocks and the phengite + chlorite assemblage in pelitic rocks. Alkali-amphibole (not crossite but magnesioriebeckite) occurs only in the Kuzumaki area. In addition to chlorite, epidote and albite, metamorphic minerals such as prehnite, pumpellyite and stilpnomelane are widespread in mafic rocks. These minerals and mineral assemblages suggest that the pumpellyite-actinolite facies metamorphism took place in all the areas. The major metamorphic minerals mentioned above were analysed by means of an electron-probe microanalyser.On the other hand, lower Cretaceous formations (the Harachiyama Formation and its correlatives) are characterized by the prehnite + pumpwllyirw association. Actinolite occurs only in the biotite zone of the thermal aureole around the Cretaceous granitic intrusion. Therefore, they have suffered the prehnite-pumpellyite facies metamorphism.