志摩半島中央部の五ケ所‐安楽島構造線から見い出された角せん岩の地質学的意義

Abstract

The Gokasho-Arashima Tectonic Line in the Chichibu Belt of the Shima Peninsula is characterized by the distribution of the huge volume of serpentinite and has been considered as eastward extension of the Kurosegawa Tectonic Zone. Two small blocks of amphibolite were found in the serpentinite of this tectonic line. These amphibolites are composed mainly of hornblende and prehnite after plagioclase. Their petrographic characteristics are similar to the amphibolite of the Kurosegawa Tectonic Zone in Kyushu, which occurrs as tectonic block in serpentinite and is altered to rodingite at the marginal part by metasomatic reaction between the amphibolite and serpentinite. Some workers suggested that the Gokasho-Arashima Tectonic Line is one of the branch fault from the Median Tectonic Line that was formed as Riedel shear during left-lateral movement of the Median Tectonic Line. Left-lateral movement of the Gokasho-Arashima Tectonic Line remobilized the pre-existed serpentinite of the Kurosegawa Tectonic Zone along the GokashoArashima Tectonic Line. So, the Gokasho-Arashima Tectonic Line now oblique to the general trend of the Chichibu Belt in the Shima Peninsula is different from the Kurosegawa Tectonic Zone in Kyushu and Shikoku.