南海岩石圈厚度变化特征及其构造意义
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摘要
地震层析资料表明,南海地区,自红河口向南经南海、苏录海到苏拉威西海,岩石圈速度低,底部横波速度仅4.4km/s,岩石圈厚度在60～80km,为薄岩石圈地区;而软流层的速度也较低,在4.2～4.4km/s,但厚度较大,大于200km。从红河—莺歌海断裂带经南海到苏录海,存在一条北西向宽约200km的上地幔北西向低速带,速度在4.05～4.25km/s(面波速度)。它反映了新生代南海地区上地幔的动力学过程。南海岩石圈厚度变化存在明显差异,南海陆缘,岩石圈厚度在70～80km,而在南海洋盆之下,岩石圈厚度超过100km,岩石圈底部存在高速岩石层,并且洋盆下的岩石圈之厚度比大陆边缘厚,在海盆岩石圈下部的60～80km深度上存在一高速层,纵波速度为8.2～8.3km/s。特别是中央海盆及西北海盆与西南海盆,其下部岩石圈中均存在一高速岩石层,这是非常具有构造意义的。由此笔者提出大陆岩石圈裂离、上地幔因减压而部分熔融所产生的基性岩浆形成南海新生代洋壳的猜想。
Seismic tomography data obtained in the South China Sea area show that,from the Red River Mouth through the South China Sea and the Sulu Sea to the Celebes Sea,the lithospheric velocity is relatively low,and the lithospheric thickness varies in the range of 60-80 km,suggesting that the Red River-Yinggehai fault is a lithospheric fault.In the continental margins of the South China Sea the lithospheric thickness ranges between 70 and 80 km,whereas in the oceanic basin the lithospheric thickness is over 100 km.In addition,there exists a high-velocity layer with velocities of 8.2-8.4km/s in the depth of 60-80 km under the South China Sea basin.These phenomena are very interesting,hence the authors consider that,when the lithosphere experienced breakup before the seafloor spreading,the lithospheric upper mantle of the Mesozoic South China Sea was subjected to decompression by more than 10 kb.This means that lithospheric upper mantle could produce partial melting if there existed 0.1% water.If there existed 10% partial melting in the upper mantle,the melting basic igneous rock could form an oceanic crust 5 km in thickness.Therefore,the authors held that there existed no mantle plume under the South China Sea area.The authors' guess is a scientific guess concerning the formation of the Cenozoic South China Sea basin.
Seismic tomography data obtained in the South China Sea area show that,from the Red River Mouth through the South China Sea and the Sulu Sea to the Celebes Sea,the lithospheric velocity is relatively low,and the lithospheric thickness varies in the range of 60-80 km,suggesting that the Red River-Yinggehai fault is a lithospheric fault.In the continental margins of the South China Sea the lithospheric thickness ranges between 70 and 80 km,whereas in the oceanic basin the lithospheric thickness is over 100 km.In addition,there exists a high-velocity layer with velocities of 8.2-8.4km/s in the depth of 60-80 km under the South China Sea basin.These phenomena are very interesting,hence the authors consider that,when the lithosphere experienced breakup before the seafloor spreading,the lithospheric upper mantle of the Mesozoic South China Sea was subjected to decompression by more than 10 kb.This means that lithospheric upper mantle could produce partial melting if there existed 0.1% water.If there existed 10% partial melting in the upper mantle,the melting basic igneous rock could form an oceanic crust 5 km in thickness.Therefore,the authors held that there existed no mantle plume under the South China Sea area.The authors' guess is a scientific guess concerning the formation of the Cenozoic South China Sea basin.
引文
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[17]廖其林,王振明,李振江,等.福州-泉州-汕头地区地壳结构的爆炸地震研究[J].地球物理学报,1986,3(3):270-280.Liao Qilin,Wang Zhenming,Li Zhenjiang,et al.The explosion seismic researching on the crustal structure of Fuzhou-Quanzhou-Shuantou[J].Acta Geophysica Sinica,1986,3(3):270-280(in Chinese with English abstract).
[18]Jacobs J A.Deep Interior of the Earth[M].Printed in Great Britain by Page Bros,Norfolk,Chapman&Hall,1992.
[19]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.Yao Bochu.The crustal structure of the north margin of the South China Sea and its significance[J].Marine Geology&QuaternaryGeology,1998,18(2):1-16(in Chinese with English abstract).
[20]姚伯初,万玲,等.中国南海海域岩石圈三维结构及演化[C]//中国岩石圈三维结构丛书之八.北京:地质出版社,2006.Yao Bochu,Wan Ling,et al.The Three-dimensional structure of lithosphere and evolution in the South China Sea[C]//In Series of Monographs on the Three-dimensional Structure of Lithosphere in China.Beijing:Geological Publishing House,2006(in Chinese with English abstract).
[21]Whitmarsh A,et al.Proceedings of the Ocean Drilling Program,Scientific Results,volume173,2001.
[2]Ludwig W J.Profiler-sonobuoy measurement in the South China Sea Basin[J].J.of Geophysical Research,1979,84:3505-3518.
[3]Yao Bochu,Wang Guangyu.Crustal structure of the South China Sea Basin[J].Science in Chinese(Series B),1983,26(6):649-661.
[4]姚伯初,曾维军,陈艺中,等.南海北部陆缘东部的地壳结构[J].地球物理学报,1993,37(1):44-53.Yao Bochu,Zeng Weijun,Chen Yizhong,et al.The crustal structure in the eastern part of northern margin of the South China Sea[J].Acta Geophysica Sinica,1993,37(1):44-53(in Chinese with English abstract).
[5]蔡学林,朱介寿,曹学敏,等.东亚西太平洋巨型裂谷体系岩石圈与软流圈结构及动力学[J].中国地质,2002,29(3):234-245.Cai Xueling,Zhu Jieshou,Cao Xueming,et al.The lithospheric and rheospheric structure of the East Asian and the Pacific rifting system and dynamics[J].Geology in China,2002,29(4):234-245(in Chinese with English abstract).
[6]薛万俊.南海地貌图[C]//南海地质地球物理图集.广州:广东科技出版社,1987.Xue Wanjun.Explanation for map of geomorphology[C]//Atlas of Geology and Geophysics of South China Sea.Guangzhou:Guangdong Science&Technology Press,1987(in Chinese).
[7]鲍才旺.南海地形图[C]//南海地质地球物理图集.广州:广东科技出版社,1987.Bao Caiwang.Explanation for map of topography[C]//Atlas ofGeology and Geophysics of South China Sea.Guangzhou:Guangdong Science&Technology Press,1987(in Chinese).
[8]Ben-Avraham Z,Uyeda S.The evolution of the China basin and the Mesozoic paleogeography of Borneo[J].Earth and Planet.Sci.Lett.,1973,18:365-375.
[9]Taylor B,Hayes D E.The tectonic evolution of the South China Sea Basin[C]//Hayes D E(ed.).The tectonic and geologic evolution of Southeast Asia seas and islands,Geophysical Monograph,AGU,Washington,1980,23:89-104.
[10]陈圣源.南海磁力异常图[C]//南海地质地球物理图集.广州:广东科技出版社,1987.Chen Shenyuan.Explanation for map of magnetic anomaly[C]//Atlas of Geology and Geophysics of South China Sea.Guangzhou:Guangdong Science&Technology Press,1987(in Chinese).
[11]何廉声.南海地质构造图[C]//南海地质地球物理图集.广州:广东科技出版社,1987.He Liansheng.Explanation for map of tectonics[C]//Atlas of Geology and Geophysics of South China Sea.Guangzhou:Guangdong Science&Technology Press,1987(in Chinese).
[12]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.Lv Wenzheng.The characteristics of magnetic anomalies and its tectonic significance in central basin of South China Sea[J].Acta Ocenologica Sinica,1987,9(1):69-78(in Chinese with English abstract).
[13]姚伯初.南海海盆在新生代的构造演化[C]//南海地质研究.武汉:中国地质大学出版社,1991:9-23.Yao Bochu.Tectonic evolution of the South China Sea in Cenozoic[C]//Geological Research of South China Sea.Wuhan:China University of Geoscience Press,1991:9-23(in Chinese with English abstract).
[14]姚伯初,曾维军,Hayes D E,等.中美合作调研南海地质专报[M].武汉:中国地质大学出版社,1994.Yao Bochu,Zeng Weijun,Hayes D E,et al.The Geological Memoir of South China Sea Surved Jointly by China and USA[M].Wuhan:China University of Geoscience Press,1994(in Chinese with English abstract).
[15]姚伯初.南沙海槽的构造特征及其构造演化史[C]//南海地质研究.武汉:中国地质大学出版社,1996,8:1-14.Yao Bochu.Tectonic characterstics and evolution of the Nansha trough[C]//Geological Research of South China Sea,Wuhan:China University of Geoscience Press,1996,8:1-14(in Chinese with English abstract).
[16]姚伯初.南海北部陆缘新生代构造运动初探[C]//南海地质研究.武汉:中国地质大学出版社,1993,5:1-12.Yao Bochu,The explanation of tectonic in north margin of South China Sea[C]//Geological Research of South China Sea.Wuhan:China University of Geoscience Press,1993,5:1-12(in Chinese with English abstract).
[17]廖其林,王振明,李振江,等.福州-泉州-汕头地区地壳结构的爆炸地震研究[J].地球物理学报,1986,3(3):270-280.Liao Qilin,Wang Zhenming,Li Zhenjiang,et al.The explosion seismic researching on the crustal structure of Fuzhou-Quanzhou-Shuantou[J].Acta Geophysica Sinica,1986,3(3):270-280(in Chinese with English abstract).
[18]Jacobs J A.Deep Interior of the Earth[M].Printed in Great Britain by Page Bros,Norfolk,Chapman&Hall,1992.
[19]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.Yao Bochu.The crustal structure of the north margin of the South China Sea and its significance[J].Marine Geology&QuaternaryGeology,1998,18(2):1-16(in Chinese with English abstract).
[20]姚伯初,万玲,等.中国南海海域岩石圈三维结构及演化[C]//中国岩石圈三维结构丛书之八.北京:地质出版社,2006.Yao Bochu,Wan Ling,et al.The Three-dimensional structure of lithosphere and evolution in the South China Sea[C]//In Series of Monographs on the Three-dimensional Structure of Lithosphere in China.Beijing:Geological Publishing House,2006(in Chinese with English abstract).
[21]Whitmarsh A,et al.Proceedings of the Ocean Drilling Program,Scientific Results,volume173,2001.
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