| 由高密度磁异常测量数据分析南海海盆的扩张年龄与扩张模式 |
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| 引用本文： | 宋陶然,李春峰.由高密度磁异常测量数据分析南海海盆的扩张年龄与扩张模式[J].地球物理学进展,2012,27(4):1432-1442. |
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| 作者姓名： | 宋陶然 李春峰 |
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| 作者单位： | 同济大学海洋地质国家重点实验室,上海,200092 |
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| 基金项目： | 国家重点基础研究发展计划(2007CB411702);国家自然科学基金(91028007,40876022);教育部高等学校博士学科点专项科研基金(20100072110036)联合资助 |
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| 摘 要： | 南海是西太平洋最大的边缘海,地处欧亚板块、太平洋板块和印度洋板块的交汇处.过去通过磁异常条带对比分析南海扩张年龄的研究很多,但是所依赖的资料有限.本文对南海海盆高密度大批量磁异常测量数据进行了系统分析,实现了平面2D磁异常数据的带通滤波处理,消除了短波长噪音和由深部下地壳和上地幔顶部磁源体引起的长波长背景信息,因此突出了海底扩张所引起的磁异常条带.利用CK95地磁倒转模型和Talwani磁异常正演方法,对南海东部和西南次海盆内的重点磁异常测线进行了正演分析.通过对不同测线之间、不同海盆之间以及同一条测线中的正演磁异常与实测磁异常之间进行对比分析,进一步验证了南海东部次海盆的扩张年龄为32～16.5 Ma;西南次海盆可能的扩张年龄仍具有较大不确定性,可能为42～33 Ma或者24～16 Ma.不同的时间模型所依赖的扩张速率的变化情况不同,全扩张速率随时间变化明显,但主要在40～80 km/Ma之间.单纯根据目前的磁异常资料很难确定西南次海盆与东部次海盆之间的扩张次序.单期次扩张模式很难解释中南断裂两侧的构造物理差异,这种差异可能主要受控于其基底岩石成分、岩石磁化率、岩浆活动、扩张速率以及深部物质冷却磁化的影响,基底深度的变化也对观测磁异常的强度有所影响.相对地,大部分扩张后玄武岩海山的存在对观测的磁异常的影响不明显,针对目前磁异常解释中不可避免的多解性问题,需要运用其他不同的手段和方法,譬如大洋钻探和深拖高分辨率磁异常测量等,来实现对南海不同次海盆扩张年龄的精确估计.我们目前的工作是通向对深拖高分辨率磁异常、船测和航测磁异常、以及卫星磁异常综合解释的第一步.
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| 关 键 词： | 南海 磁异常 正演 扩张年代 扩张模式 滤波 |
The opening ages and mode of the South China Sea estimated from high-density magnetic tracks |
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| SONG Tao-ran
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LI Chun-feng.The opening ages and mode of the South China Sea estimated from high-density magnetic tracks[J].Progress in Geophysics,2012,27(4):1432-1442. |
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| Authors: | SONG Tao-ran LI Chun-feng |
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| Institution: | (State Key Laboratory of Marine Geology,Tongji University,Shanghai 200092,China) |
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| Abstract: | The South China Sea is the largest marginal sea located at the junction of the Eurasian,Pacific and Indian Ocean plates.Previous efforts in dating the oceanic crust here are based primarily on very limited numbers of magnetic surveys.Here we take advantage of high-density digital magnetic tracks compiled from multiple surveys to enhance magnetic anomalies caused by the shallow basaltic layer via 2D band-pass filtering.This operation effectively reduces short-wavelength noises and suppresses long-wavelength background anomalies due mostly to deep magnetic sources in the lower crust and uppermost mantle.We then model filtered marine magnetic anomalies along key 2D profiles within the East and Southwest Sub-basins based on the Talwani modeling technique and the geomagnetic polarity time scale CK95.After comparing calculated with observed magnetic anomalies,the age of the East Sub-basin was estimated to be 32-16.5 Ma;the age of seafloor spreading in the Southwest Sub-basin is still ambiguous,being either 42-33 Ma or 24-16 Ma with different spreading rates.The estimated full spreading rates appear to vary markedly with time,primarily between 40-80 km/Ma.Apparently magnetic anomalies alone are insufficient in resolving the opening sequence of the two sub-basins.Models with a single episode of seafloor spreading are inconsistent with the abrupt magnetic contrast between the East and Southwest Sub-basins.These magnetic differences between the two sub-basins are caused by differences in basement mineralization and magnetization,magmatism,spreading rate,and cooling and magnetization at the lower crust and uppermost mantle.Interestingly,most post-spreading basaltic seamounts seem to have little contribution to observed magnetic anomalies.Given the current inevitable nonuniqueness in magnetic data interpretation,other techniques such as deep drilling and deep-tow magnetic surveys are needed in the future to gain fine timings on the spreading of different sub-basins of the South China Sea.Our current work is the first step toward a fully integrated interpretation on deep-tow,marine,airborne and satellite magnetic data. |
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| Keywords: | South China Sea magnetic anomalies modeling age of seafloor spreading spreading mode filtering |
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