[S-CG48] Ocean Floor Geoscience

[SCG48-08] Dynamics of back-arc basin formation with slab stagnation

*Tomoeki Nakakuki¹ (1.Earth and Planetary Systems Science Program, Graduate School of Advanced Science and Engineering, Hiroshima University)

Keywords:Back-arc basin, Slab rollback, Stagnant slab, Mantle transition zone

Aiming to understand mechanical aspects of back-arc basin formation with the slab stagnation, assessment of observed kinematic and geometrical data for the subduction zone is performed. The results are interpreted combined with reviewing recent numerical studies focusing on the slab dynamics. The data analysis revealed that backward trench motion in many subduction zones is strongly related to back-arc extension and slabs stagnating at the depth of 660 km. Tendency for the trench migration direction to depend on the subducting plate motion is also observed. These relationships correspond to self-gravitational slab rollback induced by slab interaction with the 660-km phase boundary as the most prevailing mechanism for the back-arc basin formation. The 660-km deep slabs indicate slow subducting motion with fast trench migration or shallow dip angle of their deep section. The slab dip angle and the subducting plate motion are inferred to significantly determine slab evolution subsequent to the stagnation.