南海西南海盆地震反射特征及其形成时代
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摘要
利用横穿西南海盆的地震剖面,结合声纳浮标资料获得的海盆中沉积物及基底的速度结构,同时结合陆上的钻井分层,并与邻区的沉积盆地地层进行对比,在西南海盆中划分出T2、T3、T4、T5、Tg5个反射界面。T5界面之下的沉积层对应的年龄约为27Ma,即西南海盆在早渐新世开始扩张;T4界面以上的沉积层在海盆中基本呈披覆式沉积。因此,海盆停止扩张的年龄应该在16Ma左右,即西南海盆的扩张时段为早渐新世—中中新世。穿过中央海盆的地震剖面显示海盆中的沉积层结构与西南海盆相似,由此推测这两个海盆的海底扩张时代相近,可能是同一次海底扩张的产物。
By using the seismic profiles across the southwest subbasin and the velocity structure and basement of the sediments from the sonobuoy data,together with the drilling data from the shelf that are correlated with those of the strata in the neighboring sedimentary basin, five seismic reflection boundaries have been recognized, named T2,T3,T4,T5,and Tg.The geological age of the sediments under T5 is about 27 Ma,implying that the southwest subbasin began to spread in early Oligocene; the sediment layers above T4 in the basin are widely dispersed, so the age for the southwest subbasin to stop spreading was about 16 Ma.The seafloor spreading of the subbasin lasted from early Oligocene to middle Miocene. The seismic profile across the middle subbasin shows that the sediment structure is similar to that of the southwest subbasin,so the formation ages of the two subbasins of the South China Sea are very similar and they were formed by the same seafloor spreading.
By using the seismic profiles across the southwest subbasin and the velocity structure and basement of the sediments from the sonobuoy data,together with the drilling data from the shelf that are correlated with those of the strata in the neighboring sedimentary basin, five seismic reflection boundaries have been recognized, named T2,T3,T4,T5,and Tg.The geological age of the sediments under T5 is about 27 Ma,implying that the southwest subbasin began to spread in early Oligocene; the sediment layers above T4 in the basin are widely dispersed, so the age for the southwest subbasin to stop spreading was about 16 Ma.The seafloor spreading of the subbasin lasted from early Oligocene to middle Miocene. The seismic profile across the middle subbasin shows that the sediment structure is similar to that of the southwest subbasin,so the formation ages of the two subbasins of the South China Sea are very similar and they were formed by the same seafloor spreading.
引文
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[2] TaylorB,HayesDE.TheOriginandHistoryoftheSouthChinaBasin[A].TheTectonicandGeologicEvolutionofSoutheastAsianSeasandIslands[C].GeophysicalMonograph.Am.Geophys.Union,Washington,1983,27:23—56
[3] 陈圣源.南海磁力异常图[A].南海地质地球物理图集[M].广州:广东地图出版社,1987.
[4] 何廉声.南海大地构造图[A].南海地质地球物理图集[M].广州:广东地图出版社,1987.
[5] 吕文正.南海中央海盆条带磁异常特征及构造演化[J].海洋学报,1987,9(1):69—78.
[6] 姚伯初,曾维军,等.中美合作调研南海地质专报[C].北京:中国地质大学出版社,1994.141—194.
[7] BriaisA,PatriatP,TapponnierP.UpdatedinterpretationofmagneticanomaliesandseafloorspreadingstagesintheSouthChinaSea:implicationsfortheTeriarytectonicsofSoutheastAsia[J].J.Geophys.Res.,1993,98(B4):6299—6328.
[8] 黄福林.论南海的地壳结构及深部过程[J].海洋地质与第四纪地质,1986,6(1):31—42.
[9] 张训华,徐世浙.南海海盆形成演化模式初探[J].海洋地质与第四纪地质,1997,17(2):1—7.
[10] 刘建华.南海中部地震反射波特征及其地质解释[J].海洋学报,2000,22(6):73—80.
[11] 周效忠,姜绍仁.礼乐滩—珠江口地震剖面构造地层解释及对比[A].南沙群岛及其邻近海区地质地球物理及岛礁研究论文集(二)[C].北京:科学出版社,1994.8—15.17
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