穿越南沙礼乐滩的海底地震仪广角地震试验
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摘要
本文对穿越礼乐滩东北部向西北方向延伸进入中央海盆长369 km的广角地震剖面OBS973-2进行了反演研究,以期了解南海南部陆缘的地壳结构,同时探讨南、北陆缘的共轭问题.结果表明OBS973-2剖面的速度模型中三个沉积层的速度分别为1.8～2.0 km/s、2.0～2.7 km/s和3.5～4.0 km/s;沿剖面沉积层总体上较薄或缺失.礼乐滩上地壳厚约9～10 km,速度为5.5～6.4 km/s,顶部存在小型火山;下地壳厚约11 km,速度为6.6～7.1 km/s.过渡区和海盆的上地壳厚约4～5 km,速度为5.9～6.1 km/s;下地壳厚约2～4 km,速度为6.6～6.9 km/s.从总体上看,海盆和过渡区的地壳厚度偏小,显示了拉伸减薄作用,速度分层显示陆壳比较典型,而洋壳和过渡壳的上地壳速度比标准洋壳偏高.莫霍面总体从陆坡向海盆方向较快速地抬升,在礼乐滩埋深约23 km,在海盆中的埋深8～12 km,海盆中的莫霍面顶部速度8.0 km/s,要明显小于礼乐滩下方的8.2 km/s.将OBS973-2剖面与北部陆缘的OBS2006-1剖面进行了对比,结果表明两者速度结构极为类似,讨论认为礼乐滩与中沙块体互为共轭.进而根据西北次海盆的宽度、礼乐滩与中沙块体的距离及前人提出的南海海盆的扩张时代,计算了扩张速率.
The wide angle seismic profile OBS973-2 that extends 369 km in NW-SE direction from the northeastern Liyue Bank to the central sub-basin is established by trial-and-error 2D ray-tracing method.This profile is compared with that in the northern continental margin for discussing the conjugation relationship between the northern margin and the southern margin. The velocity model consists of seven layers,i.e.water layer three sediment layers,upper crust, lower crust and upper mantle.The velocities of the three sediment layers are 1.8～2.0 km/s, 2.0～2.7 km/s and 3.5～4.0 km/s respectively.The sediment layers are thin in general and absent in some parts.There are some small volcanoes on the top of the crust in Liyue Bank and P wave velocities downward increase from 5.5～6.4 km/s in the upper crust(9～10 km thick) to 6.6～7.1 km/s in the lower crust(11 km thick).In the transition zone and sea basin P wave velocities downward increase from 5.9～6.1 km/s in the upper curst(4～5 km thick) to 6.6～6.9 km/s in the lower crust(2～4 km thick).The crust in the transition zone and sea basin shows some tectonic effect of stretching and thinning.The velocity structure of the model indicates that its continental crust is a standard one but its oceanic upper crust has relatively higher velocity than standard one.The seaward rising depth of Moho is 23 km in Liyue Bank and 8～12 km in the sea basin.The velocity beneath Moho is 8.0 km/s in sea basin,obviously smaller than 8.2 km/s in Liyue Bank.The comparison of profile OBS973-2 with a previous profile OBS2006-1 in the northern margin shows the remarkable similarity between them.This result and detailed discussion suggests a possibility of conjugation relationship between Liyue Bank and Zhongsha Massif,separated by the central seamount chain of the South China Sea.Furthermore, we calculate the seafloor spreading rate of the northwestern sub-basin and the southwestern sub-basin.
The wide angle seismic profile OBS973-2 that extends 369 km in NW-SE direction from the northeastern Liyue Bank to the central sub-basin is established by trial-and-error 2D ray-tracing method.This profile is compared with that in the northern continental margin for discussing the conjugation relationship between the northern margin and the southern margin. The velocity model consists of seven layers,i.e.water layer three sediment layers,upper crust, lower crust and upper mantle.The velocities of the three sediment layers are 1.8～2.0 km/s, 2.0～2.7 km/s and 3.5～4.0 km/s respectively.The sediment layers are thin in general and absent in some parts.There are some small volcanoes on the top of the crust in Liyue Bank and P wave velocities downward increase from 5.5～6.4 km/s in the upper crust(9～10 km thick) to 6.6～7.1 km/s in the lower crust(11 km thick).In the transition zone and sea basin P wave velocities downward increase from 5.9～6.1 km/s in the upper curst(4～5 km thick) to 6.6～6.9 km/s in the lower crust(2～4 km thick).The crust in the transition zone and sea basin shows some tectonic effect of stretching and thinning.The velocity structure of the model indicates that its continental crust is a standard one but its oceanic upper crust has relatively higher velocity than standard one.The seaward rising depth of Moho is 23 km in Liyue Bank and 8～12 km in the sea basin.The velocity beneath Moho is 8.0 km/s in sea basin,obviously smaller than 8.2 km/s in Liyue Bank.The comparison of profile OBS973-2 with a previous profile OBS2006-1 in the northern margin shows the remarkable similarity between them.This result and detailed discussion suggests a possibility of conjugation relationship between Liyue Bank and Zhongsha Massif,separated by the central seamount chain of the South China Sea.Furthermore, we calculate the seafloor spreading rate of the northwestern sub-basin and the southwestern sub-basin.
引文
[1]Taylor B,Hayes D E.The tectonic evolution of the South China Sea Basin.In:Hayes D E,ed.The Tectonic and Geologic Evolution of Southeast Asian Seas and Islands. Geophys.Monogr.AGU,Washington,D.C.,1980,23: 89-104
[2]Taylor B,Hayes D E.Origin and history of the South China Sea Basin.In:Hayes D E,ed.The Tectonic and Geologic Evolution of Southeast Asian Seas and Islands.Geophys. Monogr.,AGU,Washington,D.C.,1983,27.23-56
[3]Briais A,Patriat P,Tapponnier P.Updated interpretation of magnetic anomalies and seafloor spreading Stages in the South China Sea;implications for the Tertiary tectonics of Southeast Asia.J.Geophy.Res.,1993,98(B4):6299-6328
[4]姚伯初,王光宇.南海海盆在新生代的构造演化.南海地质研究,1991,(3):9-23 Yao B C,Wang G Y.The tectonic evolution in the South China Sea basin during the Cenozic.Geological Research of South China Sea(in Chinese),1991,(3):9-23
[5]Yao B,Zeng W,Hayes D E,Spangler,S.The Geological Memoir of South China Sea Surveyed jointly by China and the U.S.A.Wuhan:The Press of Chinese Geological University,1994
[6]姚伯初.南海西南海盆海底扩张及构造意义.南海地质研究,1997,(9):20-36 Yao B C.The sea floor spreading in the SW subbasin of South China Sea and its tectonic significance.Geological Research of South China Sea(in Chinese),1997,(9):20- 36
[7]姚伯初.南海断裂特征及其构造意义.见:姚伯初等主编.南海西部海域地质构造特征和新生代沉积.北京:地质出版社,1999.32-43 Yao B C.The characteristics and tectonic significance of the faults in the South China Sea.In:Yao et al,eds.The Tectonic Characteristic and Cenozoic Sediment in the Western Part of the South China Sea(in Chinese).Beijing:Geological Publishing House,1999.32-43
[8]Barckhausen U,Roeser H A.Seafloor spreading anomalies in the South China Sea revisited.In:Continent-Ocean Interactions within East Asian Marginal Seas,AGU Chapman Conference,San Diego,CA,ETATS-UNIS(11/ 2002),2004,149:121-125
[9]Nissen S S,Hayes D E,Buhl P,et al.Deep penetration seismic soundings across the northern margin of the South China Sea.J.Geophys.Res.,1995,100(B11):22407- 22433
[10]Yan P,Zhou D,Liu Z S.A crustal structure profile across the northern continental margin of the South China Sea. Tectonophysics,2001,338(1):1-21
[11]Qiu X L,Ye S Y,Wu S M,et al.Crustal structure across the Xisha Trough,northwestern South China Sea.Tectonophysics, 2001,341(1-4):179-193
[12]Wang T K,Chen M K,Lee C S,et al.Seismic imaging of the transitional crust across the northeastern margin of the South China Sea.Tectonophysics,2006,412(3-4):237- 254
[13]阮爱国,牛雄伟,吴振利等.潮汕坳陷中生代沉积的折射波2D速度结构和密度.高校地质学报,2009,15(4):522- 528 Ruan A G,Niu X W,Wu Z L,et al.The 2D velocity and density structure of the Mesozoic sediments in the Chaoshan Depression.Geological Journal of Ckina Universities(in Chinese),2009,15(4):522-528
[14]阮爱国,丘学林,李家彪等.中国海洋深地震探测与研究进展.华南地震,2009,29(2):10-18 Ruan A G,Qiu X L,Li J B,et al.Wide aperture seismic sounding in the margin seas of China.South China Journal of Seismology(in Chinese),2009,29(2):10-18
[15]吴振利,李家彪,阮爱国等.南海西北次海盆地壳结构:海底广角地震实验结果.中国科学(D辑):地球科学,2011, 41(10):1463-1476 Wu Z L,Li J B,Ruan A G,et al.Crustal structure of the northwestern sub-basin,South China Sea:Results from a wide-angle seismic experiment.Science in China Series(D) (in Chinese),2011,41(10):1463-1476
[16]吴振利,阮爱国,李家彪等.南海南部海底地震仪试验及初步结果.海洋学研究,2010,28(1):55-60 Wu Z L,Ruan AG,Li J B,et al.New progress of deep crust sounding in the southern margin of the South China Sea using ocean bottom seismometers.Journal of Marine Sciences(in Chinese),2010,28(1):55-60
[17]薛彬,阮爱国,李湘云等.SEDISⅣ型短周期自浮式海底地震仪数据校正方法.海洋学研究,2008,26(2):98-102 Xue B,Ruan A G,Li XY,et al.The seismicdata corrections of short period auto-floating ocean bottom seismometer.Journal of MarineSciences(in Chinese), 2008,26(2):98-102
[18]丁巍伟,李家彪.南海南部陆缘构造变形特征及伸展作用.见:南海大陆边缘动力学及油气资源潜力第5次学术讨论会论文摘要集,2011.63-64 Ding W W,Li J B.The deformation characteristics and extension effect of the southern margin of SCS.In:The Abstract Collections of the 5~(th) Conference,Project of the Dynamics and Petroleum and Gas Potential of the Continental Margin of SCS(in Chinese).2011.63-64
[19]姚伯初,王光宇.南海海盆的地壳结构.中国科学(B辑), 1983,(2):177-186, Yao B C,Wang G Y.Crustal structure of South China Sea basin.Science in China Series(B)(in Chinese),1983,(2): 177-186
[20]Ditmar P G,Makris J.Tomographic inversion of 2-D WARP data based on Tikhonov regularization:66th Ann.Internat. Mtg.,Soc.Expl.Geophys.,Expanded Abstract,1996. 2015-2018.
[21]Kudrass H R,Weidicke M,Cepek P,et al.Mesozoic and Cainozoic rocks dredged from the South China Sea(Reed Bank area) and Sulu Sea and their significance for platetectonic reconstructions.Mar.Pet.Geol.,1986,3(1): 19-30
[22]Sales A O,Jacobsen E C,Morado J A A,et al.The petroleum potential of deep-water northwest Palawan Block GSEC 66.Journal of Asian Earth Sciences,1997,15(2): 217-240
[23]Li J B.The rifting and collision of the South China Sea terrain system.Proceedings of 30th Geological Congress, 1997,13:33-46
[24]Sun Z,Zhou D,Wu S M,et al.Patterns and dynamics of rifting on passive continental margin from shelf to slope of the northern South China Sea:evidence from 3D analogue modeling.Journal of Earth Science,2009,20(1):136-146
[25]姚伯初.南海海盆新生代的构造演化史.海洋地质与第四纪地质,1996,16(2):1-13 Yao B C.Tectonic evolution of the South China in Cenozic. Marine Geology & Quaternary Geology(in Chinese),1996, 16(2):1-13
[26]姚伯初.中南礼乐断裂的特征及其构造意义.南海地质研究,1994,(7):1-14 Yao B C.Characteristics and tectonic meaning of Zhongnan-Lile Fault.Geological Research of South China Sea,1994, (7):1-14
[27]庞雄,陈长民,彭大钧等.南海珠江深水扇系统及油气.北京:科学出版社,2007.35-36 Pang X,Chen C M,Peng D J,et al.The Pearl River Deep-Water Fan System & Petroleum in the South China Sea(in Chinese).Beijing:Science Publishing House,2007.35-36
[28]Braitenberg C,Wienecke S,Wang Y.Basement structures from satellite-derived gravity field:South China Sea ridge.J. G.R.,2006,111:B05407,doi:10.1029/2005JB003938
[2]Taylor B,Hayes D E.Origin and history of the South China Sea Basin.In:Hayes D E,ed.The Tectonic and Geologic Evolution of Southeast Asian Seas and Islands.Geophys. Monogr.,AGU,Washington,D.C.,1983,27.23-56
[3]Briais A,Patriat P,Tapponnier P.Updated interpretation of magnetic anomalies and seafloor spreading Stages in the South China Sea;implications for the Tertiary tectonics of Southeast Asia.J.Geophy.Res.,1993,98(B4):6299-6328
[4]姚伯初,王光宇.南海海盆在新生代的构造演化.南海地质研究,1991,(3):9-23 Yao B C,Wang G Y.The tectonic evolution in the South China Sea basin during the Cenozic.Geological Research of South China Sea(in Chinese),1991,(3):9-23
[5]Yao B,Zeng W,Hayes D E,Spangler,S.The Geological Memoir of South China Sea Surveyed jointly by China and the U.S.A.Wuhan:The Press of Chinese Geological University,1994
[6]姚伯初.南海西南海盆海底扩张及构造意义.南海地质研究,1997,(9):20-36 Yao B C.The sea floor spreading in the SW subbasin of South China Sea and its tectonic significance.Geological Research of South China Sea(in Chinese),1997,(9):20- 36
[7]姚伯初.南海断裂特征及其构造意义.见:姚伯初等主编.南海西部海域地质构造特征和新生代沉积.北京:地质出版社,1999.32-43 Yao B C.The characteristics and tectonic significance of the faults in the South China Sea.In:Yao et al,eds.The Tectonic Characteristic and Cenozoic Sediment in the Western Part of the South China Sea(in Chinese).Beijing:Geological Publishing House,1999.32-43
[8]Barckhausen U,Roeser H A.Seafloor spreading anomalies in the South China Sea revisited.In:Continent-Ocean Interactions within East Asian Marginal Seas,AGU Chapman Conference,San Diego,CA,ETATS-UNIS(11/ 2002),2004,149:121-125
[9]Nissen S S,Hayes D E,Buhl P,et al.Deep penetration seismic soundings across the northern margin of the South China Sea.J.Geophys.Res.,1995,100(B11):22407- 22433
[10]Yan P,Zhou D,Liu Z S.A crustal structure profile across the northern continental margin of the South China Sea. Tectonophysics,2001,338(1):1-21
[11]Qiu X L,Ye S Y,Wu S M,et al.Crustal structure across the Xisha Trough,northwestern South China Sea.Tectonophysics, 2001,341(1-4):179-193
[12]Wang T K,Chen M K,Lee C S,et al.Seismic imaging of the transitional crust across the northeastern margin of the South China Sea.Tectonophysics,2006,412(3-4):237- 254
[13]阮爱国,牛雄伟,吴振利等.潮汕坳陷中生代沉积的折射波2D速度结构和密度.高校地质学报,2009,15(4):522- 528 Ruan A G,Niu X W,Wu Z L,et al.The 2D velocity and density structure of the Mesozoic sediments in the Chaoshan Depression.Geological Journal of Ckina Universities(in Chinese),2009,15(4):522-528
[14]阮爱国,丘学林,李家彪等.中国海洋深地震探测与研究进展.华南地震,2009,29(2):10-18 Ruan A G,Qiu X L,Li J B,et al.Wide aperture seismic sounding in the margin seas of China.South China Journal of Seismology(in Chinese),2009,29(2):10-18
[15]吴振利,李家彪,阮爱国等.南海西北次海盆地壳结构:海底广角地震实验结果.中国科学(D辑):地球科学,2011, 41(10):1463-1476 Wu Z L,Li J B,Ruan A G,et al.Crustal structure of the northwestern sub-basin,South China Sea:Results from a wide-angle seismic experiment.Science in China Series(D) (in Chinese),2011,41(10):1463-1476
[16]吴振利,阮爱国,李家彪等.南海南部海底地震仪试验及初步结果.海洋学研究,2010,28(1):55-60 Wu Z L,Ruan AG,Li J B,et al.New progress of deep crust sounding in the southern margin of the South China Sea using ocean bottom seismometers.Journal of Marine Sciences(in Chinese),2010,28(1):55-60
[17]薛彬,阮爱国,李湘云等.SEDISⅣ型短周期自浮式海底地震仪数据校正方法.海洋学研究,2008,26(2):98-102 Xue B,Ruan A G,Li XY,et al.The seismicdata corrections of short period auto-floating ocean bottom seismometer.Journal of MarineSciences(in Chinese), 2008,26(2):98-102
[18]丁巍伟,李家彪.南海南部陆缘构造变形特征及伸展作用.见:南海大陆边缘动力学及油气资源潜力第5次学术讨论会论文摘要集,2011.63-64 Ding W W,Li J B.The deformation characteristics and extension effect of the southern margin of SCS.In:The Abstract Collections of the 5~(th) Conference,Project of the Dynamics and Petroleum and Gas Potential of the Continental Margin of SCS(in Chinese).2011.63-64
[19]姚伯初,王光宇.南海海盆的地壳结构.中国科学(B辑), 1983,(2):177-186, Yao B C,Wang G Y.Crustal structure of South China Sea basin.Science in China Series(B)(in Chinese),1983,(2): 177-186
[20]Ditmar P G,Makris J.Tomographic inversion of 2-D WARP data based on Tikhonov regularization:66th Ann.Internat. Mtg.,Soc.Expl.Geophys.,Expanded Abstract,1996. 2015-2018.
[21]Kudrass H R,Weidicke M,Cepek P,et al.Mesozoic and Cainozoic rocks dredged from the South China Sea(Reed Bank area) and Sulu Sea and their significance for platetectonic reconstructions.Mar.Pet.Geol.,1986,3(1): 19-30
[22]Sales A O,Jacobsen E C,Morado J A A,et al.The petroleum potential of deep-water northwest Palawan Block GSEC 66.Journal of Asian Earth Sciences,1997,15(2): 217-240
[23]Li J B.The rifting and collision of the South China Sea terrain system.Proceedings of 30th Geological Congress, 1997,13:33-46
[24]Sun Z,Zhou D,Wu S M,et al.Patterns and dynamics of rifting on passive continental margin from shelf to slope of the northern South China Sea:evidence from 3D analogue modeling.Journal of Earth Science,2009,20(1):136-146
[25]姚伯初.南海海盆新生代的构造演化史.海洋地质与第四纪地质,1996,16(2):1-13 Yao B C.Tectonic evolution of the South China in Cenozic. Marine Geology & Quaternary Geology(in Chinese),1996, 16(2):1-13
[26]姚伯初.中南礼乐断裂的特征及其构造意义.南海地质研究,1994,(7):1-14 Yao B C.Characteristics and tectonic meaning of Zhongnan-Lile Fault.Geological Research of South China Sea,1994, (7):1-14
[27]庞雄,陈长民,彭大钧等.南海珠江深水扇系统及油气.北京:科学出版社,2007.35-36 Pang X,Chen C M,Peng D J,et al.The Pearl River Deep-Water Fan System & Petroleum in the South China Sea(in Chinese).Beijing:Science Publishing House,2007.35-36
[28]Braitenberg C,Wienecke S,Wang Y.Basement structures from satellite-derived gravity field:South China Sea ridge.J. G.R.,2006,111:B05407,doi:10.1029/2005JB003938
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