Evolution of Subductions Indicated by Melanges in Taiwan

Two melange zones occur in Taiwan: the Lichi Melange in the Coastal Range of eastern Taiwan and the Kenting Melange in the Hengchun Peninsula of southern Taiwan. Because of the southward propagation of the Taiwan orogen, these two melanges now crop out at the western front of the Coastal Range (Lichi Melange) and the west side of the southern Central Range (Kenting Melange). These two melanges are similar in appearance and controversial in origin, being interpreted either as subduction complexes, or as olistostromes. Remnants of neighbouring strati,graphic units, present as slices or clasts in the melange zones, shed light on the nature and origin of these two melanges and help deciphering the tectonic evolution of Taiwan orogen and its leading subductions. Based oil multiple lines of evidence, including fossil age, clay mineral composition and nature of exotic ophiolitic blocks, we conclude that the Kenting Melange zone, which was probably active over a long period of Late Cenozoic time, was a direct result of subduction process, as a relict of subduction fault zone at the front of the Taiwan accretionary prism. The Lichi Melange, for which the fossil age indicates a shorter Pliocene time span, was part of the Northern Luzon Trough forearc; it is regarded as a collision melange formed during forearc closure in probable relation with arcward backthrusting, when the Luzon arc started to collide with the Eurasian continent margin following subduction of the oceanic crust of the forearc area. After comparing the geological situation of these two melanges, we obtain a new perspective for the evolution of a trench-prism system, from subduction to arc-continent collision.