南海东北部高磁异常带成因的地球物理反演研究
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摘要
南海东北部的高磁异常带是南海北部磁场最显著的特征,目前对其成因尚有不同推测。选取一条穿越该异常带的剖面,在多道地震解释及相关地质资料的约束下进行地球物理反演研究,验证其晚中生代俯冲增生带模式的可行性。结果表明,在东沙隆起带的前新生代基底中2.5—6km的深度上、宽约150km、密度2.65 g.cm-3、剩余磁化强度700×10-3A.m-1的中生代中酸性火山岩带可产生南海东北部的高磁异常带,与浙闽东部高磁异常带的成因相同,与晚中生代古太平洋向东亚陆缘的俯冲有关。
The high magnetic anomaly belt is the most prominent feature in the northeastern South China Sea.Several explanations on its origin have been proposed.This paper selected a profile across the high magnetic anomaly belt for a gravity-magnetic inversion constrained by multichannel seismic data.The result indicates that the high magnetic anomaly!may be generated by a about 150 km wide magnetic body at depth of 2.5—6km in the pre-Cenozoic basement.This body has residual magnetization of 700×10-3A·m-1 and density of 2.65 g·cm-3,and may be interpreted as intermediate to acid volcanic rocks similar to the volcanic rocks in the eastern Zhejiang and Fujian provinces.This validates the model that the high magnetic anomaly belt in the northeastern South China Sea was generated by a buried volcanic arc associated with the Late Mesozoic subduction of the paleo-Pacific plate under the SE Eurasian margin.
The high magnetic anomaly belt is the most prominent feature in the northeastern South China Sea.Several explanations on its origin have been proposed.This paper selected a profile across the high magnetic anomaly belt for a gravity-magnetic inversion constrained by multichannel seismic data.The result indicates that the high magnetic anomaly!may be generated by a about 150 km wide magnetic body at depth of 2.5—6km in the pre-Cenozoic basement.This body has residual magnetization of 700×10-3A·m-1 and density of 2.65 g·cm-3,and may be interpreted as intermediate to acid volcanic rocks similar to the volcanic rocks in the eastern Zhejiang and Fujian provinces.This validates the model that the high magnetic anomaly belt in the northeastern South China Sea was generated by a buried volcanic arc associated with the Late Mesozoic subduction of the paleo-Pacific plate under the SE Eurasian margin.
引文
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[21]NISSEN S S,HAYES D E,BUHL P,et al.Deep penetra-tion seismic soundings across the northern margin of theSouth China Sea[J].Journal of Geophysical Research,1995,(B11):22 407—22 434.
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[25]NOAA/NGDC,BODC,GEBCO.GEBCO One Minute Grid-ded bathymetry data[EB/OL].http:∥www.bodc.ac.uk/data/online_delivery/gebco/,2003.
[2]NAKANISHI M,TAMAKI K,KOBAYASHI K.Mesozo-ic magnetic anomaly liniations and seafloor spreading historyof the northwestern Pacific[J].Geophys Res,1989,(B11):15 437—15 462.
[3]周蒂,孙珍,陈汉宗,等.南海及其围区中生代岩相古地理和构造演化[J].地学前缘,2005(3):204—219.
[4]ZHOU X M,LI W X.Origin of Late Mesozoic igneousrocks in Southeastern China:implications for lithospheresubduction and underplating of mafic magmas[J].Tectono-physics,2000,(3):269—287.
[5]李显武,周新民.古太平洋岩石圈消减与中国东南部晚中生代火成岩成因———岩石圈消减与玄武岩底侵相结合模式的补充证据[J].大地构造与成矿学,2001,(2):55—63.
[6]LI Z X,LI X H.Formation of the 1300-km-wide intracon-tinental orogen and postorogenic magmatic province in Mes-ozoic South China:A flat-slab subduction model[J].Geology,2006,(2):179—182.
[7]王家林,王一新,万明浩.石油重磁解释[M].北京:石油工业出版社,1991:58—70.
[8]陆志刚,陶奎元,谢家莹,等.中国东南大陆火山地质及矿产[M].北京:地质出版社,1997:73—239.
[9]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,1997,(7):27—35.
[10]中国科学院南海海洋研究所.南海地质构造与陆缘扩张[M].北京:科学出版社,1988:144—146.
[11]TAYLOR B,HAYES D E.Tectonic Evolution of the SouthChina Sea Basin[M].Am Geophys Union.GeophysicalMonograph,1980:89—104.
[12]HOLLOWAY N H.North Palawan Block,Philippines;itsrelation to Asian mainland and role in evolution of SouthChina Sea[J].AAPG Bulletin,1982,(9):1355—1383.
[13]吴湘杰,周蒂,庞雄,等.白云凹陷地球物理场及深部结构特征[J].热带海洋学报,2005,(2):61—69.
[14]地质矿产部第二海洋地质调查大队.南海地质地球物理图集.磁力平面/平剖图[M].广州:广东省地图出版社,1987.
[15]吴湘杰.珠江口盆地白云凹陷及邻区地球物理场研究[D].广州:中国科学院南海海洋研究所,2005:1—70.
[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,(10):1024—1 031.
[17]杨少坤,林鹤鸣,郝沪军.珠江口盆地东部中生界海相油气勘探前景[J].石油学报,2002,(5):28—34.
[18]SHI X B,QIU X L,XIA K Y,et al.Characteristics of sur-face heat flow in the South China Sea[J].Journal of AsianEarth Sciences,2003,(3):265—277.
[19]阎贫,刘海龄.南海北部陆缘地壳结构探测结果分析[J].热带海洋学报,2002,21(2):1—12.
[20]WANG T K,CHEN M K,LEE C S,et al.Seismic imagingof the transitional crust across the northeastern margin of theSouth China Sea[J].Tectonophysics,2006,(3):237—254.
[21]NISSEN S S,HAYES D E,BUHL P,et al.Deep penetra-tion seismic soundings across the northern margin of theSouth China Sea[J].Journal of Geophysical Research,1995,(B11):22 407—22 434.
[22]邹和平.南海北部陆缘张裂———岩石圈拆沉的地壳响应[J].海洋地质与第四纪地质,2001,21(1):39—44.
[23]NOAA/NGDC.Sandwell World Wide Gravity AnomalyGrid[EB/OL].http:∥www.ngdc.noaa.gov/seg/cdroms/grav99v1/data/global/sandwell/,1999
[24]NOAA/NGDC.ETOPO2v2 Global Gridded 2-minute Data-base CD-ROM[EB/OL].http:∥www.ngdc.noaa.gov/mgg/global/relief/ETOPO2/ETOPO2v2—2006/,2006
[25]NOAA/NGDC,BODC,GEBCO.GEBCO One Minute Grid-ded bathymetry data[EB/OL].http:∥www.bodc.ac.uk/data/online_delivery/gebco/,2003.
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