dc.description.abstract | The Taiwan mountain belt is known as a result of the oblique collision between the Luzon arc of the Philippine Sea Plate and the Eurasian Plate, where some of the best records on arc-continent collision have been preserved. It thus offers a unique example for the study of collision belts worldwide. Most authors suggest that the mountain building has evolved through time and could be represented by a series of cross-sections from north to south as the following stages: the post-collision stage in the offshore area of northern Taiwan, southernmost Okinawa Through and Ryukyu subduction system; the collisional stage in middle Taiwan; and the pre-collision stage in the northern Manila subduction zone. Although the extensional tectonism in northern offshore Taiwan is generally agreed, a holistic understanding of its geological evolution is lacking. Based on the interpretation of stratigraphy and deformation from multi-channel seismic profiles and the existing borehole data, we use the geological features above to construct the tectonic history of the area off northern Taiwan from the compressional to extensional stages. On the basis of the model, we divided into two regions with different tectonic events: The collapsed zone is the part of the Taiwan mountain belt during the collision stage and become to collapse during the extensional stage. Whereas, the shelf basin is quite stable and involves neither collision nor extensional stage. The shelf basin and the collapsed zone are distinguished by a fault that is connected to the onshore Shanjiao Fault, which is named as Offshore Shanjiao Fault. Before 6 Ma, the collapsed zone was a part of the East China Sea shelf basin. When the northern tip of the Luzon arc collided with the Eurasian continental margin off northern Taiwan, the Offshore Shanjiao Fault is a northwesternmost thrust fault and is known as a frontal thrust boundary of the proto-Taiwan mountain belt. The Eurasian continental margin continued to be shortened and thickened by the converging Philippine Sea plate, forming several NE-SW trending thrust faults such as Yehliu Fault, Kanjiao Fault – F1, Taipei Fault – F2, Hsintien Fault – F3, and so on. NW-SE trending dextral strike-slip faults also formed to accommodate the differential stresses on both sides of the belt segments. When the collisional orogen migrates from NE to SW direction, the crust has lost its compressional support and becomes an area of crustal stretching, forming collapsed zone at ~2.6 Ma. The southwestwardly shallowing of Basal Unconformity surface toward Taiwan implies that the extensional regime has propagated from NE to SW direction in offshore northern Taiwan. The pre-existing NE-SW trending thrust faults (Offshore Shanjiao Fault, Yehliu Fault, F1, F2, and F3) became tilted block faulting in the collapsed zone, forming a series of half-grabens. The area along the F4 and F5 becomes transtensional zones, facilitating the development of the NW-SE trending submarine canyons. Due to both post-collisional subsidence and rifting of the southern Okinawa Trough, the extensional regime continues to propagate to present-day northern Taiwan. Several active faults occur near the Offshore Shanjiao Fault, indicating that the active rifting not only exists in the back-arc basin of the southern Okinawa Trough but also in Chinese continental margin. | en_US |