琼东南盆地深水区长昌凹陷地壳结构特征
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摘要
长昌凹陷位于琼东南盆地深水区,向东通过西沙海槽与南海西北次海盆相通,其近东西向的展布形态明显异于深水区其他凹陷的NE—NEE向形态,为了弄清其地壳结构,从而更好地分析凹陷的结构和演化机制,这里根据深反射地震资料、VSP资料和最新重力资料对长昌凹陷的地壳结构进行了综合地球物理模拟。结果显示:长昌凹陷北侧地壳厚度为22~24km,南侧地壳厚度约20~22km,从两侧向长昌凹陷中央地壳厚度逐渐减薄,最薄处只有2.8km;莫霍面深度与沉积基底呈镜像关系,沉积基底最深的地方莫霍面深度最浅,最浅深度距海平面13.8km;凹陷中央东部存在一层厚约4km的下地壳高速层,该层在地震剖面和层速度剖面上均可识别。
The Changchang Sag is located in the deepwater area of the Qiongdongnan Basin.It is linked with the northwestern sub-basin of the South China Sea through the Xisha Trough to the east side.The Changchang Sag trends in a nearly east-west direction,while the other basins in the deepwater area of the Qiongdongnan Basin are in NE—NEE direction.In order to better understand the crustal structure of Chang-chang Sag,deep reflection seismic profiles,VSP data and the latest marine gravity data were used for integrated geophysical simulation.The simulation results show that the crust of the north wing of the Changchang Sag is about 22~24km in thickness,but 20~22km of the south wing,decreasing greatly to the center of the Changchang Sag.The minimum thickness of the crystalline crust is 2.8km.Mirror image relationship occurs between the Moho depth and the depositional basement,and the shallowest Moho is 13.8km below the sea-level,corresponding to the deepest depositional basement.There is a high-velocity lower crust body in the east of the center of the Changchang Sag,which can be recognized on the deep reflection seismic profiles and layer velocity profiles.The crustal thickness decreases from east to west.
The Changchang Sag is located in the deepwater area of the Qiongdongnan Basin.It is linked with the northwestern sub-basin of the South China Sea through the Xisha Trough to the east side.The Changchang Sag trends in a nearly east-west direction,while the other basins in the deepwater area of the Qiongdongnan Basin are in NE—NEE direction.In order to better understand the crustal structure of Chang-chang Sag,deep reflection seismic profiles,VSP data and the latest marine gravity data were used for integrated geophysical simulation.The simulation results show that the crust of the north wing of the Changchang Sag is about 22~24km in thickness,but 20~22km of the south wing,decreasing greatly to the center of the Changchang Sag.The minimum thickness of the crystalline crust is 2.8km.Mirror image relationship occurs between the Moho depth and the depositional basement,and the shallowest Moho is 13.8km below the sea-level,corresponding to the deepest depositional basement.There is a high-velocity lower crust body in the east of the center of the Changchang Sag,which can be recognized on the deep reflection seismic profiles and layer velocity profiles.The crustal thickness decreases from east to west.
引文
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[2]Yan P,Zhou D,Liu Z S.A crustal structure profile across the northern continental margin of the South China Sea[J].Tectonophysics,2001,338(1):1-21.
[3]Qiu X L,Ye S Y,Wu S M,et al.Crustal structure across the Xisha Trough,northwestern South China Sea[J].Tectonophysics,2001,341(1):179-193.
[4]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[J].Tectonophysics,2006,412(3/4):237254.
[5]于鹏,王家林,钟慧智,等.琼东南盆地基底结构综合地球物理研究[J].中国海上油气(地质),1999,13(6):443-450.
[6]张中杰,刘一峰,张素芳,等.南海北部珠江口—琼东南盆地地壳速度结构与几何分层[J].地球物理学报,2009,52(10):2 461-2 471.
[7]赵兵,张素芳,李守林.琼东南盆地区的地壳密度和岩石结构[J].地球物理学报,2011,54(1):98-107.
[8]刘兵,吴世敏,龙根源,等.琼东南盆地基底特征及其构造演化[J].地球物理学进展,2012,27(4):1 465-1 475.
[9]陈建文.深水盆地油气勘探新领域[J].海洋地质动态,2003,19(8):38-41.
[10]周蒂,孙珍,陈汉宗.世界著名深水油气盆地的构造特征及对我国南海北部深水油气勘探的启示[J].地球科学进展,2007,22(6):561-571.
[11]张义娜,张功成,梁建设,等.琼东南盆地长昌凹陷渐新统崖城组沉积充填及烃源岩特征[J].海洋地质前沿,2012,28(5):7-14.
[12]Sandwell D T,Smith W H F.Global marine gravity from retracked Geosat and ERS-1altimetry:Ridge Segmentation versus spreading rate[J].J.Geophys.Res.,2009,114,B01411.
[13]Amante C,Eakins B W.ETOPO1 1Arc-Minute Global Relief Model:Procedures,Data Sources and Analysis[EB].NOAA Technical Memorandum NESDIS NGDC24,.2009:19pp.
[14]Mohriak W U,Bassetto M,Vieira I S.Crustal architecture and tectonic evolution of the Sergipe-Alagoas and Jacu pe basins,offshore northeastern Brazil[J].Teotonophysics,1998,288(1-4):199-220.
[15]阎贫,刘海龄.南海北部陆缘地壳结构探测结果分析[J].热带海洋,2002,21(2):1-11.
[16]黄春菊,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):1 024-1 031.
[17]周蒂,胡登科,何敏,等.深部地层时深转换中的拟合式选择问题[J].地球科学—中国地质大学学报,2008,33(4):531-537.
[18]廖计华,王华,孙志鹏,等.琼东南盆地深水区长昌凹陷构造演化及其对层序样式的控制[J].中南大学学报(自然科学版),2012,43(8):3 121-3 132.
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[20]胡卫剑,江为为,郝天珧,等.南海前新生代残留盆地分布综合地球物理研究[J].地球物理学报,2011,54(12):3 315-3 324.
[21]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):1-13.
[22]Thybo H,Maguire P K H,Birt C,et al.Seismic reflectivity and magmatic underplating beneath the Kenga Rift[J].Geophys.Res.Lett.,2000,27(17):2 745-2 748.
[23]Thybo H,Nielsen C A.Magma-compensated crustal thinning in continental rift zones[J].Nature,2009,457:873-876.
[24]Diebold J B,Stoffa P L,Buhl P.Venezuela Basin crustal structure[J].Journal of Geophysical Research,1981,86(B9):7 901-7 923.
[25]Mutter J C,Larson R L.Extension of the Exmouth Plateau,offshore northwestern Australia:Deep seismic reflection/refraction evidence for simple and pure shear mechanisms[J].Geology,1989,17(1):15-18.
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