Takeo Bamba

THE SHIMOKAWA DIABASE COMPLEX WITH SPECIAL REFERENCE TO

The Shimokawa diabase complex is mainly composed of coarse-grained and fine grained facies of ophitic textured diabase being partially associated with variolitic diabase characterized by the presence of well-pillowed structure. Recently, the present author percieved the small scale unpillowed aphanitic diabase intruded into the ophitic diabase at S-50 of L-10 level in a gallery of the Shimokawa Mine. This aphanitic diabase in question was exmained petrographycally and it was clarified that the rock properties of the aphanitic diabase is just equivalent to the pillowed one. The chemistry of the Shimokawa diabase complex indicates that the rock is wholly tholeiitic though various facies ranging from ophitic to aphanitic is distinguishable. Following is the authors consideration on the origin of the Shimokawa diabase complex: The Shimokawa diabase of initial phase is represented by the coarse-grained ophitic facies which might have been formed through the hypabyssal condition, then the intrusive niveau of the successive diabase might have been in turn upheaved, and fine-grained ophitic facies should be formed. The intrusive niveau of the Shimokawa diabase have been ultimately changed as far as nearly subaerial and the aphanitic diabase might have been formed.