Catastrophic initiation of subduction following forced convergence across fracture zones

Although the formation of subduction zones plays a central role in plate evolution, the processes and geological settings that lead to the initiation of subduction are poorly understood. Using a visco-elastoplastic model, we show that a fracture zone could be converted into a self-sustaining subduction zone after approximately 100 km of convergence. Modeled initiation is accompanied by rapid extension of the over-riding plate and explains the inferred catastrophic boninitic volcanism associated with Eocene initiation of the Izu-Bonin-Mariana (IBM) subduction zone. Using global plate reconstructions, we suggest that IBM nucleation was associated with a change in plate motion between 55 and 45 Ma. We estimate that the forces resisting IBM subduction initiation were substantially smaller than available driving forces. (C) 2003 Elsevier Science B.V. All rights reserved.