Gravity and magnetic constraints on the crustal structure and evolution of the Horeki seamount in the Izu-Ogasawara (Bonin) arc

Abstract

Data on the crustal structure, bulk composition, and eruption ages of an arc seamount were obtained in an investigation aimed at studying the spatial and temporal variations in the magma composition of an intraoceanic arc. We conducted gravity and magnetic surveys of the Horeki seamount and evaluated the density and magnetization structure using inversion and forward modeling. The seamount is located on the back-arc side of the Izu-Ogasawara arc. This seamount has an elliptical shape, a flat summit, and satellite ridges and cones on its northern and southern flanks. The flanks are consistent with a higher density anomaly, with an estimated mean density corresponding to dense basaltic rocks. A low-density anomaly is distributed in the seamount top, indicating that the top likely consists of porous basalts or differentiated rocks. The prominent circular low Bouguer gravity anomaly, which appeared in the northern part of the flat-topped summit, indicates that a light-density material fills the summit. The main body of seamount is normally magnetized. Combined with the age of the rocks, the volcanism constructing the main body may be most robust in the Gauss chron. The deeper part of seamount may consist of intrusive rocks, with induced magnetization over remanence. The eastern part of the northern ridges is reversely magnetized, while the western part is normally magnetized. These features and the ages of the sampled rocks suggest that these ridges were constructed in the Matuyama and Brunhes chrons, respectively. The southern part of the seamount flanks shows weak normal magnetization, probably caused by the small cones with different polarities of remanent magnetization.

Seismic imaging for an ocean drilling site survey and its verification in the Izu rear arc

“…It was difficult to determine the exact location for drilling there because there was only sporadic structural information in legacy seismic data (e.g. Yamashita et al, 2007;Fujiwara et al, 2009). The International Ocean Discovery Program (IODP) also needed information on the spatial configuration of crustal and sedimentary features around the proposed drilling site before operations began, to ensure the technical safety of the deep-sea operation.…”

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

“…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). Not only large-scale surveys, but also detailed analyses and surveys have specifically investigated its structural characteristics (e.g., Tsuru et al 2008;Fujiwara et al 2009). …”