Fig. 7

Cartoons illustrating how one particular segment of the slab subducts during a cycle of back-arc spreading. The distance between the two red circles corresponds to a fixed length, and their locations highlight the movement of the slab. a In the present model, the length is ~ 900 km for the case shown in Fig. 3. b In natural subduction zones, the effect of toroidal mantle flow around the slab edge will enhance trench rollback and the subducted length may be greater than shown in Fig. 7a