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

北上山脉北部主要由晚古生代-晚中生代沉积岩组成，主要受白垩纪花岗岩侵入作用的接触变质作用影响。然而，在不受后期接触变质影响的单独碎屑区中发现了低温区域变质岩，详细研究了“Hayachine构造带”和北北上带中的Kuzakai、Morioka、Manami-Yamagata和Kuzumaki地区的典型低温变质残留物。在该区，镁铁质岩石中普遍存在钠镁榴石+阳起岩组合，泥质岩石中常见多硅白云母+绿泥石组合。碱性角闪石(不是交叉斑岩，而是镁闪石)仅产于久崎地区。除了绿泥石、绿帘石和钠长石外，镁铁质岩石中还广泛存在着早辉石、闪锌矿和辉石等变质矿物。这些矿物和矿物组合表明，所有地区都发生了闪锌矿-阳起石相变质作用。用电子探针对上述主要变质矿物进行了分析，而下白垩统(Harchiyama组及相关地层)则以前白垩岩+Pumpllyirw组合为特征。阳起石只产于白垩纪花岗岩侵入体周围热晕的黑云母带中。因此，它们遭受了前驱体-黑云母相变质作用。

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.