A possible mechanism for spontaneous cyclic back-arc spreading

Abstract Back-arc spreading is a non-steady-state process exemplified by the repeated cycles of South Fiji and Lau Basins behind Tonga arc, Parece Vela Basin Mariana Trough arc. Spreading in these regions starts with rifting within volcanic arc before shifting to back-arc region where it develops into phase well-defined spreading. 2D thermo-mechanical subduction modeling incorporating transitions at depths 410 km 660 suggests presence low-viscosity low-density mantle wedge an important condition for occur. when nearly vertical slab impinges upon discontinuity causing downdip compressive stress that transmitted up resulting extensional within-arc stress. Trench retreat during causes decrease dip angle buckling slab. ceases this phase. Rifting once more vertically dipping ‘heel’ buckled again 660-km boundary. The second initially focuses but subsequently shifts leading renewed Our predicts thick (old age) weak (small yield stress) slabs, which have intermediate resistance bending, leads cyclic In contrast, continuous predicted strong slabs large no small bending (thin slabs). Geological processes such as toroidal flow around lateral edges slab, collisions buoyant lithosphere interactions third plates may roles development specific cases. However, common timescale ~ 20 Myr there general underlying control on basin formation many if not all zones. new model presented here can account main features seen Tonga-Kermadec Calabrian arcs.