碩士 / 國立中央大學 / 地球物理研究所 / 97 / South China Sea (SCS) is located in the East Asia, which is one of marginal seas in western Pacific. The northern and southern margin belong to passive continental margin and the eastern boundary of SCS is located along the Manila Trench. According to Tapponnier et al., the collision of Indian Plate and the Eurasia Plate was started in early-middle Cenozoic and caused the southeastward escape of Indochina block, eastern escape of China block and formed the left-lateral Red River Fault zone. The block and fault movements could cause the spreading of SCS. Based on the result of magnetic lineation dating, SCS started spreading in 37 Ma and stopped in 15 Ma.
The major method of this study is using multibeam bathymetry to identify the detailed seabed features on the northern margin of SCS. The seabed features including submarine canyons, lineate topographic highs, submarine volcanoes, slumping structures and submarine landslides. The lineate topographic highs are located near foot of the continental slope. Comparing seismic profiles with the past studies, we believe the volcanism highs were formed by the post-rifting mantle magma intrusion. The grouping volcanoes are locating at the Dongsha Rise area. Dongsha Rise movement was a zone of igneous activity, the igneous activity made the crust uplift and created submarine volcanoes in this area. We propose that the volcanoes were formed in the same igneous activity with Dongsha Rise (~ 5 Ma). The submarine canyon erosion formed the slump structures on the continental slope.
Based on sub-bottom profiles, we have several acoustic transparent zones (ATZ) in the shallow sediment in our study area. All the ATZ are located in three places: continental slope foots, channel of submarine canyons and foot around the volcanism highs. We believe that the deposition of debris flow can account for the ATZ layers. We have used 9 single-channel seismic profiles (SCS) from NGDC (National Geophysical Data Center) and 20 multi-channel seismic profiles (MCS) in order to compare with bathymetry and the structures. In the other hand, we made newly sediment thickness and basement depth distribution figures by these seismic profiles.
In the southwestern slope of Dongsha Rise, we have found a lot of lineate pockmarks. The sizes of pockmarks are variant, about hundreds to thousand meters in diameter. According the drilling studies, this area could have a rich potential of gas hydrate. Hence, we suggest that the pockmarks are related to the free gases. By calculating the parameters of pockmarks shape and bathymetry, we noticed that the slope gradient and contour trends of bathymetry control the size and the trend of most of pockmarks. Besides, there are many slumpings and two landslide structures in the same area. We suggest that the slumping structures may reduce the weighting of the underneath gas-hydrate, and therefore release the gas. The upward migration of free gas may finally form the pockmark structures on the seafloor.
| Identifer | oai:union.ndltd.org:TW/097NCU05134028 |
| Date | January 2009 |
| Creators | Kuan-Ting Chen, 陳冠廷 |
| Contributors | Shu-Kun Hsu, 許樹坤 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 156 |
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