南海北部陆坡海底峡谷形成机制探讨
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摘要
通过对南海北部地震剖面的解释,并结合地貌以及区域地质特征等,对发育于南海北部陆坡区的珠江口外、台湾浅滩南以及澎湖海底峡谷的地貌和构造特征进行分析和对比,并对其形成机制进行探讨。研究结果显示,各海底峡谷具有相似的走向,并均具有转向的特征,但是其形成机制却各不相同,由此形成的地貌特征也各不同:珠江口外海底峡谷的形成与珠江带来的大量陆上沉积物的搬运相关,形成了喇叭型的水道;台湾浅滩南海底峡谷的形成受到NW向断裂构造的控制,这些断裂构造形成了薄弱带,经过沉积流的侵蚀而形成狭长的水道,当进入下陆坡后由于海山的阻隔作用而转为近EW向;澎湖海底峡谷带的上段主要是由陆坡沉积流的下向侵蚀、崩塌和滑移形成的,而其下段则主要具有沿马尼拉海沟北向延伸段发育的特征。
Submarine canyons are common features on continental margins wordwide, either active or passive. Most of them are located entirely on the upper slope, while there are also some large canyons with head that deeply indent the shelfbreak. They are generally in "V" shape (erosional situation) or "U" shape (depositional situation). What makes investigation of a submarine canyon interesting is that submarine canyons are prominent topographic features on the sea floors of continental margins. They not only shape the present morphology of continental margins, but also acted as the main conduits for transferring terrestrial sediments toward the deep sea and fed the fan system. Apart from constituting an important archive for documenting the sedimentation process history of an area, submarine canyons are also studied as modern analogues for deepwater hydrocarbon reservoirs because of their association with sand-rich turbidites.The geological and morphological characteristics of the submarine canyons on the north slope of the South China Sea were studied and the forming mechanism were discussed based on the interpretation of the multi-channel seismic profiles obtained during a "973" survey and other seismic data, including the off Zhujiang River Mouth submarine canyon, the south Taiwan Bank submarine canyon and the Penghu submarine canyon. It shows that these submarine canyons have the similar orientation, the character of direction-turning, but with different forming mechanism: The off Zhujiang River Mouth submarine canyon is related with the terrestrial downslope sediment flows carried by the paleo-Zhujiang River and has the horn shape. The south Taiwan Bank submarine canyon is controlled by the faults in NW direction. These faults weaken the surface strata, and the sediments flows will develop along them. The uplift of the sea mountain in the downslope blocks the flows' way and makes them turn into EW direction. The downward erosion, excavation, and sliding by down slope sediment flows are the major forming processes in the upper part of the Penghu submarine canyon, while the lower part mainly develop along the extending of the Manila Trench where the South China Sea is subducting under the Philippine Plate.
Submarine canyons are common features on continental margins wordwide, either active or passive. Most of them are located entirely on the upper slope, while there are also some large canyons with head that deeply indent the shelfbreak. They are generally in "V" shape (erosional situation) or "U" shape (depositional situation). What makes investigation of a submarine canyon interesting is that submarine canyons are prominent topographic features on the sea floors of continental margins. They not only shape the present morphology of continental margins, but also acted as the main conduits for transferring terrestrial sediments toward the deep sea and fed the fan system. Apart from constituting an important archive for documenting the sedimentation process history of an area, submarine canyons are also studied as modern analogues for deepwater hydrocarbon reservoirs because of their association with sand-rich turbidites.The geological and morphological characteristics of the submarine canyons on the north slope of the South China Sea were studied and the forming mechanism were discussed based on the interpretation of the multi-channel seismic profiles obtained during a "973" survey and other seismic data, including the off Zhujiang River Mouth submarine canyon, the south Taiwan Bank submarine canyon and the Penghu submarine canyon. It shows that these submarine canyons have the similar orientation, the character of direction-turning, but with different forming mechanism: The off Zhujiang River Mouth submarine canyon is related with the terrestrial downslope sediment flows carried by the paleo-Zhujiang River and has the horn shape. The south Taiwan Bank submarine canyon is controlled by the faults in NW direction. These faults weaken the surface strata, and the sediments flows will develop along them. The uplift of the sea mountain in the downslope blocks the flows' way and makes them turn into EW direction. The downward erosion, excavation, and sliding by down slope sediment flows are the major forming processes in the upper part of the Penghu submarine canyon, while the lower part mainly develop along the extending of the Manila Trench where the South China Sea is subducting under the Philippine Plate.
引文
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[15]庞雄,陈长民,施和生,等.相对海平面变化与南海珠江深水扇系统的响应[J].地学前缘,2005,12(3):167-177.
[16]黄秋菊,周蒂,陈长民,等.深反射地震剖面所揭示的白云凹陷的深部地壳结构[J].科学通报,2005,50(10):1024-1031.
[17]SIBUETJ C,HSUS K,LE P C,et al.East Asia plate tectonics since15Ma:constraints fromthe Tai wan region[J].Tectono-physics,2002,344:103-134.
[18]HUANG C H,WUW Y,CHANG C P.Tectonic evolution of accretionary prismin the arc-continent collision terrane of Tai-wan[J].Tectomophysics,1997,281:31-51.
[19]丁巍伟,程晓敢,陈汉林,等.台湾增生楔的构造单元划分及其变形特征[J].热带海洋学报,2005,24(5):53-59.
[2]夏真,林涛.南海北部海底地质灾害因素[J].热带海洋,1999,18(4):91-95.
[3]吴庐山,鲍才旺.南海东北部海底潜在地质灾害类型及其特征[J].南海地质研究,2000,12:87-101.
[4]ZHOU D,RU K,CHEN HZ.Kinematics of Cenozoic extension on the South China Sea continental margin anditsi mplications for the tectonic evolution of the region[J].Tectonophysics,1995,251:161-177.
[5]姚伯初.南海北部陆缘的地壳结构及构造意义[J].海洋地质与第四纪地质,1998,18(2):1-16.
[6]黎明碧,金翔龙,李家彪,等.南海中北部陆坡凹陷沉积充填与古陆坡形态演变[J].海洋学报,2005,27(3):73-79.
[7]TAYLOR B,HAYES D,EAYLOR B,et al.The tectonic evolu-tion of the South China Sea Basin[C]//HAYES D E(eds).The Tectonic and Geologic Evolution of Southeast Asia Seas and Islands.Washington:Geophysical Monograph AGU,1980,23:89-104.
[8]BRI AIS A,PAUTOT G.Reconstructions of the South China Sea fromstructural data and magnetic anomalies[C]//JI N X,KU-DRASS H R,PAUTOT G(eds.).Marine Geology and Geophys-ics of the South China Sea.Proc.Symp.on Recent Contributions to the Geological History of the South China Sea.Beijing:ChinaOcean Press,1990:60-70.
[9]L DMANN T,WONG H K.Neotectonic regi me on the passive continental margin of the northern South China Sea[J].Tectono-physics,1999,311:113-138.
[10]SIBUETJ C,HSUS K.How was Tai wan created[J].Tecton-physics,2004,38:159-181.
[11]L DMANN T,WONG H K,WANG P X.Pilo-Quaternary sedi mentation processes and neotectonics of the northern conti-nental margin of the South China Sea[J].Marine Geology,2001,172:331-358.
[12]吴世敏,周蒂,丘学林.南海北部陆缘的构造属性问题[J].高校地质学报,2001,7(4):419-426.
[13]李家彪,金翔龙,高金耀.南海东部海盆晚期构造地貌研究[J].中国科学:D辑,2002,32(3):239-247.
[14]金庆涣.南海地质与油气资源[M].北京:地质出版社,1989:24-29.
[15]庞雄,陈长民,施和生,等.相对海平面变化与南海珠江深水扇系统的响应[J].地学前缘,2005,12(3):167-177.
[16]黄秋菊,周蒂,陈长民,等.深反射地震剖面所揭示的白云凹陷的深部地壳结构[J].科学通报,2005,50(10):1024-1031.
[17]SIBUETJ C,HSUS K,LE P C,et al.East Asia plate tectonics since15Ma:constraints fromthe Tai wan region[J].Tectono-physics,2002,344:103-134.
[18]HUANG C H,WUW Y,CHANG C P.Tectonic evolution of accretionary prismin the arc-continent collision terrane of Tai-wan[J].Tectomophysics,1997,281:31-51.
[19]丁巍伟,程晓敢,陈汉林,等.台湾增生楔的构造单元划分及其变形特征[J].热带海洋学报,2005,24(5):53-59.
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