9:45 AM - 10:00 AM
[SIT17-04] Slabs, plumes and intraplate volcanism in SE Asia
Keywords:mantle dynamics, subduction zone, mantle plume, intraplate volcanism
High-resolution P-wave velocity (Vp) tomography of the crust and mantle down to 1600 km depth beneath SE Asia is determined by inverting more than 1.3 million P wave travel-time data of local, regional and teleseismic events recorded at 1241 seismic stations deployed in SE Asia and China. Both seismic and aseismic portions of subducted plates in different parts of the circular subduction system in SE Asia are clearly revealed as high-Vp bodies in our tomographic images. The intraplate volcanoes in Borneo are underlain by significant low-Vp anomalies in the upper mantle, whereas a clear high-Vp anomaly is visible in the mantle transition zone (MTZ) and the lower mantle. Our results suggest that hot and wet upwelling flows in the big mantle wedge above the stagnant slab in the MTZ may have caused the intraplate volcanism in Borneo. A large low-Vp anomaly consisting of a flat head and a twisted tail extending to the bottom of our model is imaged beneath the SE Asian basalt province. The low-Vp anomaly may reflect a hot zone whose shape may have been modified by mantle wind associated with plate rotation. The hot zone has a lower-mantle origin and may contain some small mantle upwellings inside, with the Hainan plume being a major trunk. We also determined 3-D Vp azimuthal anisotropy beneath SE Asia, which suggests that upwelling of the Hainan plume is resisted by the stagnant slab in the MTZ, resulting in divergent fast-velocity directions of azimuthal anisotropy beneath the stagnant slab. These results of seismic tomography and azimuthal anisotropy provide important new information on the complex mantle structure and dynamics of the SE Asian region, in particular, the subducting slabs and the Hainan plume, as well as their interactions.