HR: 1340h
AN: T33B-0528    [Abstracts]
TI: Along-arc variation of tomographic results and volcanisms may be explained by a small-scale convection under the island arc
AU: * Honda, S
EM: honda@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Yoshida, T
EM: tyoshida@mail.tains.tohoku.ac.jp
AF: Institute of of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, 6-3, Aramaki-aza-Aoba, Aoba-ku, Sendai, 980-8578 Japan
AB: The advancementr of geological and geophysical studies shows that there are small-scale (< ?sim 100km) along-arc variations of tomographic results and volcanisms. These small-scale variations may imply that the plate-scale phenomena, that is, mantle convection, may not be directly related to these phenomena. However, since the viscosity may be lowered caused by the water dehydrated from the subducting slab in the mantle wedge whose typical spatial-scale is ?sim 100 km, the mantle convection may still play a role. Recently, we considered this possibility by a series of numerical models and they are applied to the NE Honshu subduction zone, In this presentation, we summarize our results of modeling efforts and present the new results with oblique/non-oblique subduction and different dip angles. By doing so, we show that the temporal and spatial evolution of arc-volcanisms in the NE Honshu and Izu-Bonin arcs may be explained, at least, qualitatively by our model. In the NE Honshu arc, the spatial distribution of volcanisms, which correlate with the tomographic results, exhibits several clusters elongated almost perpendicular to the arc and the possible migration of volcanisms from the back-arc side to the volcanic front side, at least, during last 5 Myrs. The pattern of clusters appears to have flip-flopped around 5 Ma. In the Izu-Bonin arc, there are a series of across-arc seamount chains, where volcanic activities occurred from ?sim 17 Ma to ?sim 3Ma, similar to the clusters of the NE Honshu arc, though the recent active rifting occurs almost parallel to the arc. Based on our numerical experiments, we show that above-mentioned features can be explained, at least, qualitatively by our model. Also we obtained a several inferences from our hypothesis. In the NE Honshu arc, the geometry of subduction from the old time (say ?sim 20 Ma) to the present remained similar. Meanwhile, in the Izu-Bonin arc, the angle of dip of subducting plate may have increased. This may explain the disappearance of volcanisms along the seamount chains of the Izu-Bonin arcs at present. We also suggest that the trend of seamount chains, which is oblique to the arc, may be a result of the lateral movement of the back-arc region after their formation.
DE: 7299 General or miscellaneous
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
SC: Tectonophysics [T]
MN: Fall Meeting 2005