| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 98 === Northern Luzon Arc extends northward from the Luzon Island to Taiwan, with Babuyan, Batan, Lanyu and Lutao volcanic islands in between. Its northernmost portion has accreted to the island of Taiwan and become the Coast Range of Taiwan by the arc-continent collision processes. In the framework of arc-continent collision, the area south of 21°30’ N is a typical subduction zone, the area between 21°30’ N and 22°45’ N is the incipient arc-continent collision zone, and the area north of 22°45’ N is a mature arc-continent collision zone. This study analyzes a series of seismic reflection profiles that cross the eastern flank of the northern Luzon Arc to image structural characteristics of the arc basement and overlying sediment from south to north, from the typical subduction zone to the mature arc-continent collision zone.
Three major sequence boundaries identified on the seismic profile, in the Huatung Basin are used to identify the degree of crustal deformation of the northern Luzon Arc eastern flank area. From seismic reflection profiles, the topography and geological structures along the eastern flank of the arc can be divided into three zones based on the degree of deformation. From south to north, they are the typical subduction zone, the incipient arc-continent collision zone, and the mature arc-continent collision zone.
In the typical subduction zone, the basement and sediments are little deformed. The sediments conformably deposited in the slope basin between the northern Luzon Arc and the East Ridge of Luzon Arc, and some sediments deposited on top of the arc.
In the incipient arc-continent collision zone, an N-S trending east vergent thrust fault has developed in arc-slope area between the northern Luzon Arc and the Huatung Basin. This thrust fault not only offsets the sequence boundaries in the Huatung Basin, but also extends downward to deform the volcanic basement. We speculate that this fault may separate the Luzon Arc basement from the Huatung basin basement.
In the mature arc-continent collision zone, the N-S trending east vergent thrust continues to extend northward. A thrust fault is observed in the area between 22°45’ N and 23°N where the northern Luzon Arc becomes the Coast Range of Taiwan Island. North of 23°30’ N, this thrust fault develops into a series of branch fault, which could be the result of Huatung basin basement gradually subducted beneath the Eurasian plate.
In the study area, sediments are mostly deposited in the intra-arc slope basins or in the arc-slope area. The sediment thickness increases northward and toward Taiwan orogenic belt. In the arc-slope area north of 23°30’ N, there are numerous submarine canyons and submarine mass movement features, indicating that this area is a very unstable depositional environment.
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