Structural characteristics of the Bayonnaise Knoll caldera as revealed by a high-resolution seismic reflection survey

Mikiya Yamashita,Shuichi Kodaira,Takafumi Kasaya,Narumi Takahashi,Kaoru Takizawa

doi:10.1186/s40623-015-0214-2

Abstract

The Bayonnaise Knoll caldera is a conical silicic caldera located on the eastern part of the back-arc rift zone of the Izu-Ogasawara arc. Many geological and geophysical surveys have shown that the Bayonnaise Knoll caldera contains hydrothermal sulfide deposits. The Japan Agency for Marine-Earth Science and Technology conducted high-resolution multi-channel seismic reflection surveys across the Bayonnaise Knoll caldera to ascertain details of the crustal structure, such as the configuration of faults around the caldera. A reflection profile of excellent quality was obtained by high-density velocity analysis at about 150-m intervals. We applied prestack depth migration by using the results of the high-density velocity analysis and further analyzed this region. The depth-migrated profile shows many faults, which correspond to bathymetric lineations, on the eastern side of the Bayonnaise Knoll caldera. The velocity structure of the Bayonnaise Knoll caldera resembles that of the Myojin Knoll caldera, which has been well surveyed and is associated with the hydrothermal deposit. The depth-migrated profile shows a clear reflective zone that is distributed asymmetrically to the Bayonnaise Knoll caldera center. These data suggest that caldera formation was controlled by back-arc rifting activity in the Izu-Ogasawara arc. The hydrothermal fluid migration path in the Bayonnaise Knoll caldera is estimated to be the result of faulting and magmatic intrusion on the eastern side of the structure. It is assumed that these fluids formed the Kuroko-type sulfide deposit in the eastern part of the caldera structure.

Highlights

The Izu-Ogasawara (Bonin) arc extends over 1,200 km from the Honshu island of Japan to Guam on the northeastern margin of the Philippine Sea plate
As described in this paper, we investigated the fault configuration and the crustal structure of the Bayonnaise Knoll caldera with a high-density velocity analysis of newly obtained multichannel seismic reflection (MCS) data
We propose a strategy for how to locate the hydrothermal deposit in the Bayonnaise Knoll caldera

Summary

Introduction

The Izu-Ogasawara (Bonin) arc extends over 1,200 km from the Honshu island of Japan to Guam on the northeastern margin of the Philippine Sea plate. The Izu-Ogasawara arc is a region that is beneficial for understanding intra-oceanic evolution, and it has been investigated well in many geological and geophysical studies (e.g., Taylor 1992; Suyehiro et al 1996; Kodaira et al 2007). Large-scale surveys, and detailed analyses and surveys have investigated its structural characteristics (e.g., Tsuru et al 2008; Fujiwara et al 2009). Paleo-volcanic arrangements are known to exist along the north-south direction; these are known as the outerarc high or frontal-arc high by geographic characteristics in the forearc basin. Several basins developed in the so-called back-arc rift zone between the current volcanic front and the paleo-volcanic arrangement in the west (Murakami 1996)

Results

Discussion

Conclusion