11:30 AM - 11:45 AM
[SCG60-03] Development of a 3D thermal structure in the subduction zone due to a low viscosity layer at the plate interface
3D finite element models are used to investigate the effects of LVL on the thermal structure. The model domain is divided into four parts: the crust, a small portion of the mantle wedge tip which is rigid, the viscous mantle wedge, and the subducting slab. The model is exactly the same in the along-arc direction. The flow is computed only in the viscous mantle wedge, whereas temperature is computed for the whole model domain. When the viscosity in LVL is relatively high, the slab and mantle are effectively decoupled but there is no along-arc variation in the flow and thermal structure. I find, however, that when the viscosity in LVL is sufficiently low the corner flow starts to show 3D features and it leads to the along-arc temperature variation. It is well known that the distribution of Quaternary volcanoes in the northeast Japan forms clusters whose characteristic wavelength is around 80 km. The model proposed here successfully explains the observed wavelength based on an assumption which is simpler and better constrained by observations compared to previous models.
A previous study has proposed that slab and mantle are decoupled down to a common depth (70-80 km) for most subduction zones. It means that the LVL considered in this study could exist for other subduction zones as well. Therefore, the new model proposed here can be applied to a wide range of regions.