As an active collision zone between the Luzon arc and the China continental 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 to crustal stretching and rifting as a result of flipping of subduction from the northwest-facing Luzon arc system to the south-facing Ryukyu arc system. Taiwan and its neighboring southern Ryukyu used to be part of the rifted China continental margin before the collision started in late Miocene time. Engineered by the northwest movement of the Philippine Sea plate in the past 5 m.y., the north-south–trending Luzon arc obliquely overrode the northeast-southwest–trending continental margin and tectonized it into a collision orogen that progressively enlarged and migrated from northeast to southwest. Following the southwest-propagating collision, the north-dipping Philippine Sea plate, which was subducting beneath the Ryukyu arc, 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 subjected to lithospheric stretching induced by the trench suction. The collision orogen collapsed as a result of crustal thinning, and its central part foundered into a deep submerged basin. A whole spectrum of active tectonic scenarios, ranging from orogenic buildup by collision to orogenic collapse by rifting and subsidence, can be readily observed in the Taiwan-Ryukyu area and provides a vivid example for the process of orogenic collapse.

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