Meeting room "Glova", 4 floor, Integrated Research Building
Abstract
Effects of physical properties in the mantle transition zone on the dynamics of the subducting slab are studied using a stagnant slab using two-dimensional dynamical models of the integrated plate-mantle system with freely movable subducting and overriding plates. We first investigated dynamical mechanisms of formation and avalanche of stagnant slabs. Parameters of the slab rheology and phase transition are systematically changed to produce various styles of stagnating or penetrating slabs that interact with the 410-km and 660-km phase transitions. Our simulated results show importance of trench retreat and slab's rheological property in the transition zone. Slab plasticity that memorizes the shape produced by past deformation generates slab stagnation at various depths around the 660-km phase transition. The slab stagnates even beneath the 660-km phase boundary, with a gentle Clapeyron slope. Slab viscosity also determines the final state of the subducted slab. A low-viscosity slab due to grain-size reduction at 660-km depth can finally penetrate into the lower mantle because the growth time of the Rayleigh-Taylor instability is shorter. We next examine dynamical mechanisms for the back-arc basin formation. In our simulation, the main driving force of the back-arc extension is slab backward motion. The backward motion is generated gravitational instability when the slab is largely deformed at the 660-km phase transition. The back-arc stress is however determined by the overriding plate motion. The back-arc extension is generated when the overriding plate is not movable. This may provide a possible explanation of the asymmetric distribution of back-arc basins between the west and east Pacific.
For inquiry：Yasuhiro Kuwayama TEL:（089）927-8408
E-mail kuwayama@sci.ehime-u.ac.jp
