TECTONIC EVOLUTION OF ACCRETIONARY PRISM IN THE ARC-CONTINENT COLLISION TERRANE OF TAIWAN

The thick sedimentary and meta-sedimentary rocks west of the Eocene-Pa leozoic metamorphic basement of Taiwan represent an accretionary prism developed between the Eurasian continent and the Philippine Sea plate . The accretionary prism consists of a subduction wedge in the east an d a collision prism in the west. The deep-marine subduction wedge deve loped during the eastward subduction of the South China Sea oceanic cr ust since the Early Miocene. In the Central Range, a regional unconfor mity with mylonite structure occurred between the Miocene deep-marine slates-turbidites and the Paleozoic-Eocene metamorphic basement. The u nconformity marks the tectonostratigraphic break between the overlying subduction wedge and the underlying underthrust Eurasian continent. T he subduction wedge extends from the western Central Range southwards through the Hengchun Peninsula to the offshore Hengchun Ridge. Subduct ion of the South China Sea oceanic crust further led to the oblique ar e-continent collision starting about 6.5 Ma in northern Taiwan. During the collision, the shallow-marine passive margin and foreland sequenc es were progressively incorporated to the collision prism by a series of west-vergent thrusts in the Hsuehshan Range and the Western Foothil ls. The Kaoping Slope west of the subduction wedge of the Hengchun Rid ge represents the modem collision prism in the active arc-continent co llision zone. The collision prism is juxtaposed against the subduction wedge to the east along the Lishan-Laonung-Hengchun fault, which exte nds offshore to the 30-km-wide fault zone between the Kaoping Slope an d the Hengchun Ridge. Before the onset of the arc-continent collision, the Lishan-Laonung-Hengchun fault developed along the northern part o f the proto-Manila trench and acted as the thrust front located to the west of the subduction wedge. At present, the thrust front has migrat ed southwestward to the west of the collision prism. The arc-continent collision propagated southwards and yielded the time-transgressive de formations from north to south to result a south tapering configuratio n of Taiwan. This paper is the first to recognize the consistent occur rence of the subduction wedge and collision prism onshore and offshore Taiwan. This allows reconstruction of the tectonic evolution of the a ccretionary prism during the subduction and collision tectonics of Tai wan.