Based on various geophysical observations at the southern Mariana arc, and assuming an extensional development of the basin behind the Mariana ridge, a hypothesis of arc evolution is advanced to account for the observations. The hypothesis proposes that at the Mariana arc, oceanic plate convergence rates within a limited range (~8 to 9 cm/yr) are necessary to initiate the partial melting at the slip zone at depths of <200 km that is believed responsible for inter-arc extension. As extension develops, plate convergence rates are increased and the dip of the descending slab is consequently decreased. When convergence rates increase to some magnitude in excess of 10 cm/yr, extension is halted, allowing convergence rates to return to the 8 to 9 cm/yr necessary to reinitiate extension. Extension, in this view, is then a self-cancelling and cyclic process.