神奈川県山北町・浅間山の隆起開始年代－伊豆弧北東端のアクティブテクトニクスに対するひとつの制約

The Sengen-yama hills, located at Yamakita town, Kanagawa Prefecture, Japan, represent the upthrown block along the E-W trending Hinata fault. The roughly 5-km long Hinata thrust fault is a segment of a long bell-shaped splay of faults (the Tanna, Hirayama, Hinata and Kozu-Matsuda faults) developed at the collision zone of Honshu island and Izu-Mariana arc. We found old fluvial gravel deposits and an overlying pumice fall deposit near the top of the hills. The pumice fall deposit is identified to be the Fuji-Yoshioka tephra (F-YP; 70-80 ka) on the basis of phenocryst assemblages, refractive index of the heavy minerals and facies association. Based on geology and tephra correlation, the onset of emplacement of the Sengen-yama hills is determined to be 70-80ka. According to previous studies, the initiation of the faults occurred about 100 ka. Close spatial correlation and close onset ages of these faults suggest that they were formed and developed in the same tectonic regime.