Computer animations of a plate tectonic model for the Cenozoic development of the region of SE Asia and the SW Pacific illustrate the importance of extension during collision. In the past 10 Ma plate boundaries have shifted rapidly, and GPS measurements provide a snapshot of the changing tectonic setting. From about 25 Ma the New Guinea passive margin collided with the Philippines-Halmahera-South Caroline Arc, the Australian margin began to collide with the SE Asian margin in Sulawesi, and the

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... ntong Java Plateau collided with the Melanesian Arc. These collisions caused a major change in the character of plate boundaries between about 25 and 20 Ma. Until about 12 Ma much of the sector between Sulawesi and Fiji was dominated by strike-slip faulting and local subduction but this situation changed at about 12 Ma as old oceanic lithosphere entered the trench west of New Guinea, and new subduction zones developed east of New Guinea. The Banda Sea and Woodlark Basin illustrate the speed of change, the unexpected interplay of convergence and extension, and the importance of subduction as the cause of change. Immediate causes of extension within the orogenic system include strike-slip movements, effects of hinge roll-back, and pull forces of subducting slabs. High resolution dating is required to identify extensional events but the animations portray almost simultaneous contraction and extension which may be characteristic of many orogenic belts.