Why Does the Higashi-Izu Monogenetic Volcano Group Exist in the Izu Peninsula?: Relationships between Late Quaternary Volcanism and Tectonics in the Northern Tip of the Izu-Bonin Arc.

Abstract

A synthesis of available geological, petrological, and geophysical data was made to construct a model for explaining the relationships between the late Quaternary volcanism (the Higashi-Izu monogenetic volcano group, HIMVG) and tectonics in and around the Izu Peninsula, Japan. The Izu Peninsula and adjacent areas can be divided into three tectonic blocks: the western Izu (W-Izu), eastern Izu (E-Izu), and Oshima-Zenisu blocks. The vents or intrusions of the HIMVG are formed as open cracks aligning with the nearly NW-SE azimuth of horizontal maximum compression of regional stress in the E-Izu block. This stress field is mainly controlled by the NW-SE compression caused by the strong mechanical coupling of the buoyant Izu-Bonin arc with the Japan arc. In spite of this compression, the upper crust of the E-Izu block is under weak lateral constraint on northeastward extension. Both the plate geometry involving an intra-plate fracture, the West Sagami Bay Fracture, and the existence of block rotations in the northern E-Izu block probably enable the northeastward upper crust extension in the E-Izu block, and make a monogenetic volcano field, where a new dike is formed in the upper crust at each eruptive or intrusive event.

Diversity of Parent Magmas of Higashi-Izu Monogenetic Volcano Group.

“…Vent alignment 2 of Hamuro (1978) may reflect the submerged cone sheet as proposed by Miyajima et al (1985). Paleomagnetic directions and stratigraphic relationships of the erupted materials suggest linear arrangements of the vents trending NW-SE, which is consistent with the direction of the maximum compressive stress field around the Izu Peninsula (Koyama and Umino, 1991). This fact indicates that the direction of magmatic intrusion is not controlled by a local stress field around the magma chamber but is determined according to the regional stress field.…”

“…The only historic eruption of 1989 on the seafloor off the coast of Ito has shown that this volcano group is still active. Recent study on this volcano group (Koyama et al, 1990;Koyama and Umino, 1991) has suggested that it has erupted since 100 thousand years B. P., much earlier than it was thought by the previous workers (Aramaki and Hamuro, 1977;Hamuro, 1978). Total volume of erupted materials amounts to 2.5km3, one sixth of which are occupied by lava flows and pyroclastic materials ejected from Omuroyama.…”

“…The HMGV is the only known example which is located on the volcanic front along the arc-trench system. The tectonics of the HMVG is outside the scope of this paper and is discussed in detail by Koyama and Umino (1991).…”

Interpretation of Seismic and Volcanic Activities in the Izu Block in Relation to Collision Tectonics.

“…In fact, the exact location and nature of the plate boundaries in this region are the problems under debate (Nakamura and Shimazaki, 1981;Kaizuka, 1984;Ishibashi, 1978Ishibashi, , 1985Ishida, 1990;Yoshida, 1991;Koyama et al, 1991). The situation has been made more complicated by the proposal that central Honshu should be separated in the Fossa Magna region adjacent to the Izu Peninsula by a nascent plate boundary between the Eurasian and North American plates (Kobayashi, 1983;Nakamura, 1983).…”

“…The east part of the Izu block is a volcanically distinctive area in which Quaternary monogenetic volcanoes are widely distributed (Aramaki and Hamuro, 1977;Hamuro et al, 1983;Koyama et al, 1991). The 1989 volcanic eruption at Teisi Knoll is regarded as one of the activities of the monogenetic volcano group (Soya et al, 1989).…”