HR: 1340h
AN: DI33A-1127    [Abstracts]
TI: Deep Slab Subduction and Dehydration and Their Geodynamic Consequences: New Insights From Seismology and Mineral Physics
AU: Liu, L
EM: lucy@aob.geophys.tohoku.ac.jp
AF: Tohoku University, Graduate School of Science, Sendai, 980, Japan
AU: * Zhao, D
EM: zhao@aob.geophys.tohoku.ac.jp
AF: Tohoku University, Graduate School of Science, Sendai, 980, Japan
AU: Ohtani, E
EM: ohtani@mail.tains.tohoku.ac.jp
AF: Tohoku University, Graduate School of Science, Sendai, 980, Japan
AB: Fluids play important roles in the dynamics and evolution of the Earth, such as lowering the melting temperature of the mantle, transporting elements, enhancing diffusion and creep, and possibly changing the location of phase boundaries such as the 410 and 670 km discontinuities. Fluids are also intimately linked to a variety of earthquake faulting processes. In this work we present new pieces of evidence from seismology and mineral physics for the existence of significant low-velocity anomalies in the deep part of the upper-mantle wedge and the transition zone that are caused by fluids from the deep subduction and deep dehydration of the Pacific and Philippine Sea (PHS) slabs under western Pacific and East Asia. The PHS slab is found to subduct down to the mantle transition zone depth though the seismicity within the slab occurs only down to 200-300 km depths. The PHS slab dehydration has contributed to the formation of the Okinawa Trough and the Quaternary and active volcanism in SW Japan. Combining with the convective circulation processes in the mantle wedge, deep dehydration of the subducting Pacific slab has affected the morphology of the subducting PHS slab and its seismicity under SW Japan. The Pacific slab is found to stagnate in the mantle transition zone under East Asia, which has contributed to the formation of the continental rift system and intraplate volcanism in Northeast Asia (such as the active Changbai and Wudalianchi volcanoes). Slow anomalies are also found in the mantle under the subducting Pacific slab, which may represent (a) small mantle plumes, (b) mantle upwellings associated with the deep slab subduction, or (c) slab dehydration associated with deep earthquakes caused by the reactivation of large faults in the slab which are generated by the large normal-faulting earthquakes in the oceanic plate near the trench and are preserved during the slab subduction.
UR: http://www.aob.geophys.tohoku.ac.jp
DE: 8104 Continental margins: convergent
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8145 Physics of magma and magma bodies
DE: 8180 Tomography (6982, 7270)
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting