| Research Abstract |
2001: The Gokasho-Arashima Tectonic Line (G-A), which runs through the medial zone of the Chichibu Terrane of the Shima Peninsula, has been regarded as the eastern extension of the Kurosegawa Terrane of Shikoku. Geological survey and gravimetry at its western terminal clarified following two evidence; 1. G-A characterized by the serpentinite zone does not overlie the Chichibu Terrane as a tectonic nappe, but represents a longitudinal fault disecting the Chichibu Terrane. 2. Due to poor road network, gravimetry as a preliminary research of the field geological survey did not bring about any contribution. 3. In another area (Kanto Mountains), various rocks exotic to the sedimentary rocks composing the Chichibu Terrane were newly found along a narrow fault zone (Naguri Fault Zone) and this fault zone was ascertained as the eastern extremity of the Kurosegawa Terrane. Along this fault zone, a marked negative anomaly of gravity was traced and testified the usefulness of gravimetry for detecting a fault zone.
2002 : 1. Along the boundary zone of the North and Kurosegawa Terrane of the Chichibu Terrane of the Shima Peninsula, serpentinite blocks were newly discovered. These serpentinite blocks were concluded to be overlain by the rock mass of the North Terrane with a low-angled fault plane. The character of this fault was inferred by gravimetry. 2. Gravimetry was extended to the northwestern extension of the Naguri Fault Zone of the Kanto Mountains. A marked negative anomaly of gravity was traced and it strongly suggests the northwestern extension of the Naguri Fault Zone, although any rocks characteristic of the Kurosegawa Terrane have not been found in spite of detailed field survey.
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