EXTENSIONAL COLLAPSE OF THE NORTHERN TAIWAN MOUNTAIN BELT

As an active collision zone between the Luzon are and the China contin ental margin, the Taiwan mountain belt, particularly its south-central part, is undergoing crustal shortening and rapid uplift, The northern part of the orogen is, however, subjected Eo crustal stretching and r ifting as a result of flipping of subduction from the northwest-facing Luzon are system to the south-facing Ryukyu are system, Taiwan and it s neighboring southern Ryukyu used to be part of the rifted China cont inental margin before the collision started in late Miocene time, Engi neered by the northwest movement of the Philippine Sea plate in the pa st 5 m.y., the north-south-trending Luzon are obliquely overrode the n ortheast-southwest-trending continental margin and tectonized it into a collision orogen that progressively enlarged and migrated from north east to southwest, Following the southwest-propagating collision, the north-dipping Philippine Sea plate, which was subducting beneath the R yukyu are, also extended westward and caused flipping of subduction in the northern part of the collision orogen, In consequence, the orogen lost the compressive support by the colliding plates and became subje cted to lithospheric stretching induced by the trench suction, The col lision orogen collapsed as a result of crustal thinning, and its centr al part foundered into a deep submerged basin, A whole spectrum of act ive tectonic scenarios, ranging from orogenic buildup by collision to orogenic collapse by rifting and subsidence, can be readily observed i n the Taiwan-Ryukyu area and provides a vivid example for the process of orogenic collapse.