Effects of Metastable Olivine on Negative Buoyance in Subduction Zones and their Dynamic Siganificance

We calculated the negative buoyancy of subducting lithospheres based on numerical simulations of the temperature fields by means of 2-D FEM. The values of the negative buoyancy increase with depth in depths of h 740 km. On the other hand, there is a decrease of negative buoyancy in depths of 660 to 740 km, because there is phase transformation from ringwoodite to perovskite, which prevents slab penetrating into the lower mantle. Metastable olivine changes the distribution of negative buoyancy between depths of 400 to 660 km. Especially, it drastically altered the increasing trend of negative buoyancy with depth, leading to a net decrease of negative buoyancy below the 400 km depth. The existence of metastable olivine reduces the increased value of negative buoyancy with depth, which would make the penetration through 660 km discontinuity more difficult. Moreover, it would greatly change the pattern of stress distribution in and around the area of metastable olivine.