Sediment dispersal system along the Taiwan-Luzon convergentmargin in the perspective of source-to-sink

• Main Authors: Kan-Hsi Hsiung, 熊衎昕
• Other Authors: Ho-Shing Yu
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/25788830362639234302

博士 === 國立臺灣大學 === 海洋研究所 === 100 === Examining bathymetric and seismic reflection data from deep-sea region between Taiwan and Luzon, this study identified prominent morpho-sedimentary features that mainly include the South China Sea Shelf/Slope (passive margin) juxtaposed by the Kaoping Shelf/Slope (active margin) intersected by Penghu Canyon and the deep-sea Penghu Channel and northern Manila Trench farther down-slope. These three negative relief troughs of canyon, channel and trench can be interconnected and aligned in a nearly N-S direction, forming a sediment pathway along the western Taiwan-Luzon margin in the deepest east rim of the South China Sea basin. Sediments derived from adjacent Taiwan orogen and Chinese continental margin are longitudinally transported via this sediment dispersal route and are finally deposited in the northern Manila Trench. The deep-sea Penghu Channel is pivotal of the sediment dispersal system because it links the Penghu Canyon in Taiwan arc-continental collision zone to the Manila Trench in the subduction zone west of Luzon, forming a continuous regional sediment dispersal system. The Formosa Canyon on the South China Sea Slope serves mainly as a conduit for sediments derived from mainland China, feeding sediments into the Penghu Canyon, terrestrial sediments derived from southern Taiwan are mainly transported by Kaoping Canyon to the deep-sea Penghu Channel and the axial Penghu Canyon can receive shallow marine sediments from both flanked slopes, serving as a marine transport route. Most orogenic sediments derived from Taiwan are transported longitudinally by axial canyon and down-slope deep-sea channel, and other sediments are supplied laterally by canyons and gullies from flanking slopes, joining into the axial marine transport route and finally debouching to the South China Sea Basin. The morpho-sedimentary features change their morphology and sedimentary processes progressively from collision in the north to the subduction in the south due to effects of tectonics and sedimentation. Shallow canyon evolves to deep oceanic trench following increase in water depth. Narrow V-shaped canyon changes to wide asymmetrical cross-sectional morphology of the trench. The downslope sediment transport system changes from dominant erosion in the canyon to deposition in the deep-water channel and trench. This study emphasizes the significance of the sediment transport routes of the collision zone in the northernmost South China Sea by comparing that of Huon Gulf in Papua New Guinea-Solomon Sea collision zone. Both sediment dispersal systems reveal remarkable similarities in morphology of the collisional and juxtaposed slopes, forming a triangle and tilted trench-ward collisional marine basin. This study combines the axial canyon-channel developing along the convergent slopes, and canyons and gullies on the slopes merging laterally into the axial canyon-channel to form a regional sediment dispersal system with a dendritic pattern. This system is characterized by axial transport and lateral supply of sediments. This study demonstrates a sediment dispersal system in a short distance less than 300 km from the Taiwan orogen to the northern Manila Trench and provides an ideal and analog example for studying sediment dispersal system in the perspective of source-to-sink studies of other active continental margin. The Penghu Canyon, deep-sea Penghu Channel and northern Manila Trench form the axis of sediment dispersal system. Overall, tectonics controls the orientation and location of the sediment dispersal system and structure and sedimentary processes control the morphology and route of this system. About 1.6 Ma several N-S oriented submarine canyons developed in the offshore deep-water region southwest of Taiwan and initiated the early phase of development of the sediment dispersal system. Farther south, the deep-sea Penghu Channel has developed west of the uplifted bathymetric ridge produced by westward compression along the convergent zone around 1 Ma. Approximately 0.4 Ma ago, the paleo-Penghu Canyon developed with a N-S course northeast of the present-day Penghu Canyon, forming the proto-system of sediment dispersal route. The Manila Trench began to form about 15 Ma and progressively migrated westward to the present position south of the Taiwan orogen. At present, the modern Penghu Canyon links to the deep-sea Penghu Channel southward and debouches to the northern Manila Trench, resulting in a complete sediment dispersal system along the Taiwan-Luzon convergent margin.