Petrography and bulk chemical composition of the Miyako zoned pluton, Kitakami Mountains.

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  • 北上山地，宮古累帯深成岩体の岩石記載と全岩化学組成
  • キタカミ サンチ ミヤコ ルイタイ シンセイガンタイ ノ ガンセキ キサイ ト

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Abstract

Geological and petrological studies were carried out on the Miyako Granitic Body, a zoned pluton in the North Kitakami Mountains, Northeast Japan. Five different rock types are distinguished based on the modes of occurrence and megascopic character. A large part of this pluton is occupied by Miyako and Yamada rock types. The Miyako rock type is present in the northern portion of the pluton, and consists of quartz diorite and granodiorite with hornblende and biotite. The Yamada rock type is located in the southern part, and consists of granitoids similar to the Miyako rock type, but relatively more coarse-grained and leucocratic. The Ashibatai, Osawa and Shimotanabe rock types crop out in only a few places. The Ashibatai rock type consists of porphyritic monzogranite and is located near the center of the Miyako rock type. The Shimotanabe rock type is located of east of the Yamada type, while the Osawa rock type is even further to the east. Both the Shimotanabe and Osawa rock types are fine-grained and more melanocratic than the Yamada rock type.<br>     Differences between the Miyako and Yamada rock types are apparent in the modal analysis and major and trace elements. Modal and chemical trends of the Osawa rock type are similar to those of the Miyako rock type. The trends for the Shimotanabe and Osawa rock types are, as well as field observations, in general agreement with those displayed by the Yamada rock type. Thus, two distinct magmas are assumed to have been active at the same time in the Miyako Pluton.

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