Abstract: Paleozoic formation, Jurassic formation, lower and upper Cretaceous formation, Paleogene formation and granitic rocks are widely exposed in this district. The geological succession and the igneous activity are shown in Table 1.
Granitic masses are divided into two groups. The first group consists of granitic stocks such as the Taro, Kurumihata, Jofutsumori and Ojiri masses, and the second group consists of granitic masses such as the Tanohata, Hashikami and Miyako masses. The Tanohata granitic mass is divided into two rock facies, i.e., the Otomo and Moichi types. The Otomo type is composed of coarse-grained trondjhemite and granodiorite, and the Moichi type is composed of medium-grained granodiorite, quartz monzonite and quartz diorite.
The thermal metamorphosed rocks mentioned in this paper develope around the Tanohata granitic mass of the second group and are derived mainly from sediments of the Paleozoic and lower Cretaceous formations. The contact aureole around this granitic mass is divided into the following three zones:
biotite slate zone........western and eastern sides
cordierite spotted slate zone....western and eastern sides, and a part of the roof-pendant
high grade zone........western side and roof-pendant
The biotite slate and cordierite spotted slate zones are characterized by the existence of biotite and cordierite respectively. In the cordierite spotted slate zone, cordierite begins to occur prior to andalusite. The high grade zone is characterized by the coexistence of cordierite and andalusite and/or sillimanite with potash feldspar. Most of the rocks of the high grade zone, especially laminated and banded hornfelses, resemble the rocks of the Ryoke metamorphic terrain in feature and mineral paragenesis. Sillimanite is rare, and forms fibrolitic needles around biotite and andalusite crystals in the hornfelses of the western side of the granitic mass. On the contrary, sillimanite needle replaces andalusite in some hornfelses of the roof-pendant. It seems that andalusite-sillimanite transition (the first sillimanite isograd) takes place in the hornfelses of this aureoles, where the coexistence of potash feldspar and sillimanite (the second sillimanite isograd) is also found. From such relation, it seems that the first sillimanite isograd coincides with the second sillimanite isograd in this contact aureole. This is a distinct difference from the Ryoke metamorphic terrain, and this may be due to the difference in the rock pressures of the two areas.
The rocks of this aureole contain few sillimanites, andalusites and garnets compared with those of the Tono and Senmaya contact aureoles in the Kitakami Mountainland. On the other hand, potash feldspar are present generally in large amount in the rocks of this aureole. Difference of contents of metamorphic minerals and mineral paragenesis among their contact aureoles may be due not to the physical condition, but to the chemical composition of original rocks.
Potash feldspars were studied optically and by X-ray method. Potash feldspars in the rocks of the high grade zone show monoclinic symmetry. The crystallization temperatures of potash feldspars were also examined by Barth´s method.
Ferric-ferrous ratios (Fe₂O₃/Fe₂O₃+FeO) of biotites in the high grade zone are 0.05 to 0.07 and resemble those of the Senmaya aureole and the Ryoke metamorphic terrain, but they are smaller than those of the Abukuma metamorphic terrain.
Lastly, metasomatism was discussed from the compositional variation of major and minor elements. In some rocks of the high grade zone, it seems probable that potassium was introduced from granitic rock.

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