东沙群岛西南海区海底地震测线OBS2015-1揭示的深部地壳结构
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摘要
为深入理解南海北部多道地震测线D80显示的深反射信息,沿此测线布置OBS(15台)地震测线(OBS2015-1),测线长300km,方向NNW—SSE,从水深800m陆坡延伸至3760m深海平原。文章利用Obstool软件进行预处理(位置校正和时间校正等)、震相识别,利用FAST tomography软件进行速度层析成像。速度结果表明,新生代沉积层速度1.6~3.5km·s-1,厚度约2km;中生界速度3.5~5.5km·s-1,平均厚度约3km。在洋陆过渡带处,沉积基底受新生代岩浆活动影响,有较大起伏。在上陆坡处,上地壳存在向上凸起约5km的高速异常,在多道地震剖面中表现为杂乱反射的背斜构造,上覆晚新生代地层也同步形变,推测可能是新生代晚期岩浆侵入造成。地壳厚度由陆坡的23~20km减薄至洋盆的8km。地壳下部存在7.0~7.6km·s-1的高速层,高速层由陆坡的5km左右逐渐递减至海盆的2km左右,因上陆坡和洋陆过渡带晚新生代岩浆活动活跃,作者认为地壳下部高速层是由海底扩张停止后岩浆侵入形成。
To better understand deep reflectors in the multi-channel seismic profile D80 in the northern South China Sea, a coincident ocean bottom seismic survey line(OBS2015-1) with 15 OBSs was inversed. This OBS line extends ESE 300 km, from 800 m in the upper slope to 3760 m in the abyssal plain. OBS data processing includes position and time corrections, phase identification using Obstool software, and velocity inversion with FAST tomography software. The resultant velocity shows that Cenozoic strata has a velocity of 1.6-3.5 km·s-1 and a depth of 2 km. Mesozoic velocity is 3.5-5.5 km·s-1 with an average depth of 3 km. In the oceanic and continental transition zone(OCT), the sediment basement is greatly affected by Late Cenozoic magmatic activity. Obvious high velocity anomaly and isoline uplift(5 km) were detected in the upper crust of the upper slope, corresponding to chaotic reflection anticline structure in D80; and the overlying Late Cenozoic strata also presents as synchronous deformation, which may result from the Late Cenozoic magmatic intrusion. The crustal thickness decreases gradually from 23-20 km beneath the continental slope to 8 km in the oceanic basin. A high velocity(7.0-7.6 km·s-1) layer was seen in the lower crust, which changes from 5 km in the upper slope to 2 km in the ocean basin. Because of the Late Cenozoic magmatic activity in the continental slope and OCT, we interpret that the high crustal velocity layer originated from magmatic intrusion after the cession of seafloor spreading.
To better understand deep reflectors in the multi-channel seismic profile D80 in the northern South China Sea, a coincident ocean bottom seismic survey line(OBS2015-1) with 15 OBSs was inversed. This OBS line extends ESE 300 km, from 800 m in the upper slope to 3760 m in the abyssal plain. OBS data processing includes position and time corrections, phase identification using Obstool software, and velocity inversion with FAST tomography software. The resultant velocity shows that Cenozoic strata has a velocity of 1.6-3.5 km·s-1 and a depth of 2 km. Mesozoic velocity is 3.5-5.5 km·s-1 with an average depth of 3 km. In the oceanic and continental transition zone(OCT), the sediment basement is greatly affected by Late Cenozoic magmatic activity. Obvious high velocity anomaly and isoline uplift(5 km) were detected in the upper crust of the upper slope, corresponding to chaotic reflection anticline structure in D80; and the overlying Late Cenozoic strata also presents as synchronous deformation, which may result from the Late Cenozoic magmatic intrusion. The crustal thickness decreases gradually from 23-20 km beneath the continental slope to 8 km in the oceanic basin. A high velocity(7.0-7.6 km·s-1) layer was seen in the lower crust, which changes from 5 km in the upper slope to 2 km in the ocean basin. Because of the Late Cenozoic magmatic activity in the continental slope and OCT, we interpret that the high crustal velocity layer originated from magmatic intrusion after the cession of seafloor spreading.
引文
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HAO HUJUN,ZHANG XIANGTAO,YOU HONGQING,et al,2009.Characteristics and hydrocarbon potential of Mesozoic strata in eastern Pearl River Mouth Basin,Northern South China Sea[J].Journal of Earth Science,20(1):117-123.
MJELDE R,KASAHARA J,SHIMAMURA H,et al,2002.Lower crustal seismic velocity-anomalies;magmatic underplating or serpentinised peridotite?Evidence from the V?ring Margin,NE Atlantic[J].Marine Geophysical Researches,23:169-183.
NIRRENGARTEN M,GERNIGON L,MANATSCHAL G,2014.Lower crustal bodies in the M?re volcanic rifted margin:Geophysical determination and geological implications[J].Tectonophysics,636:143-157.
NISSEN S S,HAYES D E,BUHL P,et al,1995.Deep penetration seismic soundings across the northern margin of the South China Sea[J].Journal of Geophysical Research,100(B11):22407-22433.
RESTON T J,2009.The structure,evolution and symmetry of the magma-poor rifted margins of the North and Central Atlantic:A synthesis[J].Tectonophysics,468(1-4):6-27.
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WANG T K,CHEN MINGKAI,LEE C S,et al,2006.Seismic imaging of the transitional crust across the northeastern margin of the South China Sea[J].Tectonophysics,412(3-4):237-254.
WHITE R,MCKENZIE D,1989.Magmatism at rift zones:the generation of volcanic continental margins and flood basalts[J].Journal of Geophysical Research,94(B6):7685-7729.
WHITMARSH R B,BESLIER M O,WALLACE P J,1998.Return to Iberia[C]//Proceedings of the Ocean Drilling Program,Initial Reports,173.College Station,TX:Ocean Drilling Program:1-30.
WU JINMIN,1994.Evaluation and models of Cenozoic sedimentation in the South China Sea[J].Tectonophysics,235(1-2):77-98.
YAN PIN,WANG LIAOLIANG,WANG YANLI,2014.Late Mesozoic compressional folds in Dongsha waters,the northern margin of the South China Sea[J].Tectonophysics,615-616:213-223.
YAN PIN,ZHOU DI,LIU ZHAOSHU,2001.A crustal structure profile across the northern continental margin of the South China Sea[J].Tectonophysics,338(1):1-21.
ZELT C A,BARTON P J,1998.Three-dimensional seismic refraction tomography:A comparison of two methods applied to data from the Faeroe Basin[J].Journal of Geophysical Research,103(B4):7187-7210.
ZELT C A,SMITH R B,1992.Seismic traveltime inversion for2-D crustal velocity structure[J].Geophysical Journal International,108(1):16-34.
ZHAO MINGHUI,QIU XUELIN,XIA SHAOHONG,et al,2010.Seismic structure in the northeastern South China Sea:S-wave velocity and Vp/Vs ratios derived from three-component OBSdata[J].Tectonophysics,480(1-4):183-197.
吕修亚,阎贫,陈洁,等,2009.折射方法在南海北部潮汕坳陷中生界地层研究中的应用[J].热带海洋学报,28(1):43-47.LüXIUYA,YAN PIN,CEHN JIE,et al,2009.Application of refraction velocity in studing Mesozoic strata in Chaoshan Depression on northern margin of South China Sea[J].Journal of Tropical Oceanography,28(1):43-47(in Chinese).
邱燕,王立飞,黄文凯,等,2016.中国海域中新生代沉积盆地[M].北京:地质出版社:114.
邵磊,尤洪庆,郝沪军,等,2007.南海东北部中生界岩石学特征及沉积环境[J].地质论评,53(2):164-169.SHAO LEI,YOU HONGQING,HAO HUJUN,et al,2007.Petrology and depositional environments of Mesozoic strata in the Northeastern South China Sea[J].Geological Review,53(2):164-169(in Chinese).
吴振利,李家彪,阮爱国,等,2011.南海西北次海盆地壳结构:海底广角地震实验结果[J].中国科学:地球科学,41(10):1463-1476.WU ZHENLI,LI JIABIAO,RUAN AIGUO,et al,2012.Crustal structure of the northwestern sub-basin,South China Sea:Results from a wide-angle seismic experiment[J].Science China Earth Sciences,55(1):159-172.
姚伯初,曾维军,陈艺中,等,1995.南海北部陆缘东部中生代沉积的地震反射特征[J].海洋地质与第四纪,15(1):81-90.YAO BOCHU,ZENG WEIJUN,CHEN YIZHONG,et al,1995.Seismic reflective characteristics of Mesozoic sediments on the eastern continental margin in the North of the South China Sea[J].Marine Geology&Quaternary Geology,15(1):81-90(in Chinese).
张莉,张光学,王嘹亮,等,2014.南海北部中生界分布及油气资源前景[M].北京:地质出版社:208-211.
周蒂,王万银,庞雄,等,2006.地球物理资料所揭示的南海东北部中生代俯冲增生带[J].中国科学D辑:地球科学,36(3):209-218.ZHOU DI,WANG WANYIN,PANG XIONG,et al,2006.Mesozoic subduction-accretion zone in northeastern South China Sea inferred from geophysical interpretations[J].Science in China:Series D Earth Sciences,49(5):471-482.
BOILLOT G,RECQ M,WINTERER E L,et al,1987.Tectonic denudation of the upper mantle along passive margins:a model based on drilling results(ODP Leg 103,western Galicia margin,Spain)[J].Tectonophysics,132(4):335-342.
?ERVENYV,MOLOTKOV J A,PSENCIK I,1977.Ray Method in Seismology[M].Prague:Charles University Press.
CHRISTESON G,1998.OBSTOOL:Software for Processing UTIG OBS Data[M].Austin:Institute for Geophysics,University of Texas.
FRANKE D,2013.Rifting,lithosphere breakup and volcanism:comparison of magma-poor and volcanic rifted margins[J].Marine and Petroleum Geology,43:63-87.
GERNIGON L,RINGENBACH J C,PLANKE S,et al,2004.Deep structures and breakup along volcanic rifted margins:insights from integrated studies along the outer V?ring Basin(Norway)[J].Marine and Petroleum Geology,21(3):363-372.
HAO HUJUN,ZHANG XIANGTAO,YOU HONGQING,et al,2009.Characteristics and hydrocarbon potential of Mesozoic strata in eastern Pearl River Mouth Basin,Northern South China Sea[J].Journal of Earth Science,20(1):117-123.
MJELDE R,KASAHARA J,SHIMAMURA H,et al,2002.Lower crustal seismic velocity-anomalies;magmatic underplating or serpentinised peridotite?Evidence from the V?ring Margin,NE Atlantic[J].Marine Geophysical Researches,23:169-183.
NIRRENGARTEN M,GERNIGON L,MANATSCHAL G,2014.Lower crustal bodies in the M?re volcanic rifted margin:Geophysical determination and geological implications[J].Tectonophysics,636:143-157.
NISSEN S S,HAYES D E,BUHL P,et al,1995.Deep penetration seismic soundings across the northern margin of the South China Sea[J].Journal of Geophysical Research,100(B11):22407-22433.
RESTON T J,2009.The structure,evolution and symmetry of the magma-poor rifted margins of the North and Central Atlantic:A synthesis[J].Tectonophysics,468(1-4):6-27.
SAWYER D S,WHITMARSH R B,KLAUS A,1994.Explanatory notes[C]//Proceedings of the Ocean Drilling Program,Initial Reports.College Station,TX:Ocean Drilling Program:1-25.
TAYLOR B,HAYES D E,1983.Origin and history of the South China Sea basin[M]//HAYES D E.The Tectonic and Geologic Evolution of Southeast Asian Seas and Islands:Part 2.Washington,DC:American Geophysical Union,27:23-56.
WANG T K,CHEN MINGKAI,LEE C S,et al,2006.Seismic imaging of the transitional crust across the northeastern margin of the South China Sea[J].Tectonophysics,412(3-4):237-254.
WHITE R,MCKENZIE D,1989.Magmatism at rift zones:the generation of volcanic continental margins and flood basalts[J].Journal of Geophysical Research,94(B6):7685-7729.
WHITMARSH R B,BESLIER M O,WALLACE P J,1998.Return to Iberia[C]//Proceedings of the Ocean Drilling Program,Initial Reports,173.College Station,TX:Ocean Drilling Program:1-30.
WU JINMIN,1994.Evaluation and models of Cenozoic sedimentation in the South China Sea[J].Tectonophysics,235(1-2):77-98.
YAN PIN,WANG LIAOLIANG,WANG YANLI,2014.Late Mesozoic compressional folds in Dongsha waters,the northern margin of the South China Sea[J].Tectonophysics,615-616:213-223.
YAN PIN,ZHOU DI,LIU ZHAOSHU,2001.A crustal structure profile across the northern continental margin of the South China Sea[J].Tectonophysics,338(1):1-21.
ZELT C A,BARTON P J,1998.Three-dimensional seismic refraction tomography:A comparison of two methods applied to data from the Faeroe Basin[J].Journal of Geophysical Research,103(B4):7187-7210.
ZELT C A,SMITH R B,1992.Seismic traveltime inversion for2-D crustal velocity structure[J].Geophysical Journal International,108(1):16-34.
ZHAO MINGHUI,QIU XUELIN,XIA SHAOHONG,et al,2010.Seismic structure in the northeastern South China Sea:S-wave velocity and Vp/Vs ratios derived from three-component OBSdata[J].Tectonophysics,480(1-4):183-197.