関東山地五日市町層群堆積岩の岩石学的研究

概要

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The Itsukaichimachi Group is one of the Middle Micoene sedimentary sequences occurring in the Kanto Mountains. The heavy minerals of the Itsukaichimachi Group are characterized by the enrichment of spinel in its lower part. The spinel compositions are different from those in serpentinites and periodotites in the Kanto Province. Furthermore, mineral proportions and compositions throughout the sedimentary sequence are different from those in the surrounding pre-Miocene sedimentary rocks. It suggests that the constituents of the sedimetnary rocks in the Itsukaichimachi Group were not derived from the surronding pre-Miocene rocks. A shear zone with thickness of about 10m is present between the Miocene and pre-Miocene sedimentary rocks and is followed upwards by a conglomerate with alternation of reddish and greenish layers. No sedimentary structure is recognisible in the shear zone. Considering the differences of heavy minerals between the Micoene and pre-Miocene rocks, and presence of the shear zone, it is probable that the sedimentary rocks of the Itsukaichimachi Group were not deposited in situ, but they were deposited elsewhere and then tectonically brought to the present position.
国立科学博物館の論文
1990-06-22