Abstract

The transition of a passive continental margin into a subduction zone remains a hypothesis because few geological cases have been reported. The North Sulawesi subduction zone is a 5-9 myr system in Southeast Asia that has evolved from a continental passive margin and has long been overlooked by studies of passive to active margin transitions. Here we compare geophysical data from the region with numerical simulation results. We find that the initial subduction of North Sulawesi must rely on horizontal forces, while the trench retreat depends on the negative buoyancy of the oceanic lithosphere. Furthermore, less space available for subduction leads to lower mantle flow caused by subduction and slower trench retreat. These new dynamical constraints indicate that the negative buoyancy of the oceanic plate is the key factor for subduction and trench retreat, even though the subduction initiation was induced.