Blackwell Publishing AsiaMelbourne, AustraliaIARIsland Arc1038-4871© 2007 The Authors; Journal compilation © 2007 Blackwell Publishing Asia Pty Ltd? 2007162214223Research Article Island arc volcanism and convectionS. Honda et al.
Island Arc (2007) 16, 214–223
Research Article Spatial and temporal evolution of arc volcanism in the northeast Honshu and Izu-Bonin Arcs: Evidence of small-scale convection under the island arc? SATORU HONDA,1* TAKEYOSHI YOSHIDA2 AND KAN AOIKE3 1
2
Earthquake Research Institute, University of Tokyo, Tokyo 113-0032, Japan (email:
[email protected]), Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Sendai, Japan and 3Center for Deep Earth Exploration, JAMSTEC, Yokohama, Japan
Abstract Arc volcanism of the past 10 my in the northeast Honshu and Izu-Bonin Arcs shows several notable features. In the northeast Honshu Arc, the spatial distribution of volcanism exhibits several clusters elongated nearly perpendicular to the arc and the possible migration of volcanism from the back-arc side to the volcanic front side, at least, during the past 5 my. The pattern of clusters seems to have flip-flopped around 5 Ma. In the Izu-Bonin Arc, there are a series of across-arc seamount chains, in which volcanic activity occurred from ca 17 Ma to ca 3 Ma, similar to the clusters of the northeast Honshu Arc, although the recent active rifting occurs almost parallel to the arc. On the basis of studies of numerical modeling, these features might be explained, at least qualitatively, by the small-scale convection under the island arc. Several inferences can be made from our modeling results for the tectonics of the Izu-Bonin Arc. The angle of dip of subducting plate in the Izu-Bonin Arc might have increased. This can explain the disappearance of volcanism along the seamount chains and the recent along-arc volcanism with narrow rifting. The trend of seamount chains, which is oblique to the arc, might not be their intrinsic feature but rather a result of the lateral movement of the back-arc region after their formation. These inferences can be tested by the future detailed morphological and chronological studies of the Izu-Bonin Arc. Key words: arc volcanism, Izu-Bonin, northeast Honshu, small-scale convection, volcanic fingers.
INTRODUCTION Elucidating the dynamics of the mantle wedge above the subducting slab is one of the most important subjects to understand the island-arc volcanism. Traditionally, this topic is theoretically considered by 2-D models (e.g. Van Keken 2003 for a recent review). However, with the advance of geological and geophysical studies, it becomes clear that there are small-scale (
