OCR understanding of the processes by which continents rift and sea-floor spreading initiates is derived primarily from studies either of old passive margins and oceanic crust or of young regions of intra-continental extension where spreading has not yet started. It has been thought that continental rifting ceases when sea-floor spreading begins(1,2), that oceanic fracture zones develop from transfer or transform faults within continental rifts(3,4), and that linear magnetic anomalies correlate with the onset of sea-floor spreading during times of magnetic reversals(5,6). Here we present a marine geophysical survey of one of the few active examples of continental rifting and spreading initiation, the western Woodlark basin/Papuan peninsula region of New Guinea, which shows that in detail these assumptions do not hold. The data confirm models of the rifting to spreading transition that invoke both ridge propagation and nucleation of discrete spreading cells(7-10), and provide an unambiguous example of a spreading centre reorienting by synchronous jumping rather than propagation.