Olivine-spinel Phase Boundary Rheology, Strength and Deep Seismicity

In this paper,we discuss (1) whether a significant change in dominant creep mechanism will occur at 400 km discontinuity in some subducting slabs as a result of olivine-spinel phase transition;(2) could the result influence phase boundary strength and deep seismicity? Through this study,we noticed that a transition of creep mechanism from dislocation to diffusion (or superplasticity) could occur at the olivine-spinel phase boundary where temperature effect on phase transition dominates over pressure,which will result in a weakening phase boundary.Triggered by this phase transition weakening,a deep strong earthquake might be generated in the relatively strengthening region above the phase boundary so that the phase boundary is naturally the ceasing boundary of deep seismicity.Contrasting to this,the transition of the creep mechanism from dislocation glide to dislocation climb may be common at the phase boundary where pressure effect on phase transition dominates over temperature.In this case,olivine-spin

Olivine-spinel Phase Boundary Rheology, Strength and Deep Seismicity

In this paper,we discuss (1) whether a significant change in dominant creep mechanism will occur at 400 km discontinuity in some subducting slabs as a result of olivine-spinel phase transition;(2) could the result influence phase boundary strength and deep seismicity? Through this study,we noticed that a transition of creep mechanism from dislocation to diffusion (or superplasticity) could occur at the olivine-spinel phase boundary where temperature effect on phase transition dominates over pressure,which will result in a weakening phase boundary.Triggered by this phase transition weakening,a deep strong earthquake might be generated in the relatively strengthening region above the phase boundary so that the phase boundary is naturally the ceasing boundary of deep seismicity.Contrasting to this,the transition of the creep mechanism from dislocation glide to dislocation climb may be common at the phase boundary where pressure effect on phase transition dominates over temperature.In this case,olivine-spinel phase transition will result in increasing creep strength in spinel phase so that deep,strong earthquakes could be generated by a transformation faulting.We suggest that the olivine-spinel phase boundary might be a weakening boundary in a "hot" subducting slab,at which deep seismicity will be terminated,and it might be a strengthening boundary in a "cold" subducting slab so that seismic activity can penetrate down to 670 km.