The regions around New Guinea illustrate the importance of extension in a convergent setting. In all areas the ultimate driving force is subduction although local mechanisms may be different in different places. The Woodlark Basin has opened due to slab-pull forces caused by subduction beneath New Britain, and is being subducted beneath the Solomons almost as fast as it is forming. In the Banda Sea extension of the upper plate, induced by roll-back of an old slab, has proceeded from caused continental rifting to arc-continent collision. In both regions this has occurred within a period of about ten million years. There is tenuous evidence of extension during the same period in other areas of New Guinea region which may indicate that extension and convergence are typical of the whole orogenic system. The sequence of events varies from place to place but may include rapid extension with core complex formation, arc magmatism, arc splitting, ocean crust formation and subduction reversal. Subduction can eliminate very young ocean crust and there may be large and rapid local rotations.

Some of the extension may be related to strike-slip movements within the New Guinea margin. In this situation there may have been even more rapid and frequent changes from extension to contraction, related to fault geometry and plate boundary conditions which are very sensitive to small movements in rotation pole positions. These in turn are likely to be a response to changing plate boundary conditions, in particular, changing slab lengths at subduction zones.

The speeds of all these processes are very high and at present it is difficult to predict where and when extensional events could occur. The lesson from the Indonesia-New Guinea collision zone is that extension may be typical of collisional orogenesis, that the speed of processes means that high precision dating is required to recognise such events, and that extension and contraction may be effectively simultaneous.