中国大陆深探测的大地电磁测深研究
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摘要
通过对地震波速度、密度、磁性、导电性等物理场进行观测,研究地壳与上地幔的物性与结构特征,将为研究地球内部物质状态、地壳运动过程及其动力学机制等科学命题提供科学依据,同时也将为寻找深部大型矿床提供信息。大地电磁深探测方法作为研究地球壳幔电性结构的主要地球物理方法,在国内外完成了大量探测工作,取得了许多重要的研究成果。在研究壳幔构造方面,大地电磁法和地震方法一起被视为两大支柱方法,在世界范围内解决大陆动力学问题方面已有许多成功的应用范例。但由于大地电磁探测以天然电磁场作为场源,在矿集区等强干扰地区往往很难采集到高信噪比的数据,抗干扰能力较弱。同时,大地电磁与地震数据的约束反演以及联合解释目前尚没有达到实用化,这些都限制了大地电磁数据的处理及解释精度。"深部探测技术与实验研究"(SinoProbe)专项下属的"深部探测技术实验与集成"项目将选择青藏高原、西部造山带与华南山区结晶岩等复杂地质条件和不同人文干扰水平地区,以大地电磁探测与地震探测作为主要手段,研究深部精细地球物理探测技术的集成,并且通过实验剖面研究这些实验区的壳幔结构特征。其中的"大地电磁测深大剖面观测实验与壳/幔三维电性研究"课题,将通过在实验区的大地电磁观测实验,研究适用于不同地质条件及干扰水平地区的大地电磁数据采集方法技术以及精细处理与反演方法,同时探讨大地电磁数据与地震数据的约束反演以及联合解释。该研究将提高深部地球物理探测精度,为深部精细地球物理探测方法技术集成以及区域地球物理精细探测提供范例。已经完成的青藏高原东北缘西秦岭造山带和福建结晶岩地区的大地电磁观测试验表明,在这些典型地质构造区域,虽然存在施工困难,干扰水平大等各种不利因素,但只要采取合适的野外观测技术,并通过数据精细处理与反演计算,是能够获得高质量的大地电磁数据以及可靠的电阻率分布模型。试验所取得的成果,将为实现"深部探测技术实验与集成"项目科学目标和研究任务提供重要的技术支撑与保障。
By the observation of geophysical field parameters such as seismic velocity, density, magnetism, and electrical conductivity, we have obtained the physical properties and structure features of the earth's crust and upper mantle. Thus scientific evidence further facilitates the understanding of the earth's interior status, the process and mechanism of the movement of crust, and other scientific subjects. Furthermore, such useful information can also lead to the exploration of large-scale mineral deposits. As a primary geophysical method for the detection of the electrical structure of the earth's crust and mantle, magnetotelluric exploration has been widely adopted both in China and foreign countries, and numerous significant research results have been acquired. The seismic and magnetotelluric methods are recognized as two of the dominant methods on the study of the structure of the earth's crust and mantle. They have been proved to be very effective in solving worldwide continent dynamic problems by numerous application cases. However, because the natural electromagnetic field tend to be affected by noises, it is difficult for the MT method to acquire ideal data with high signal-to-noise ratio in the mineral-enriched areas with strong noises. At the same time, the technique of constraining inversion and joint interpretation for seismic and MT data is still not ready for utilization. All the reasons mentioned above limit the accuracy of the process and interpretation of MT data. The project of "experiment and integration of deep detection technology" belongs to the "SinoProbe" project. It takes different areas with both complicated geological conditions and different situation of man-made noises, like the Tibet plateau, the western orogen, and the mountain areas with crystallized rocks in the south china, as target area to study the integration of geophysical techniques for detailed deep detection by utilizing the seismic and MT methods. The electrical structures of these areas are given from the results of the experimental profiles. The subject, which is named "the MT observation experiments and the study of electrical structure of the earth's crust and mantle", will focus on the study of suitable MT acquisition and computation techniques for different noise environment and geological conditions. The constraining inversion and joint interpretation of seismic and MT data will also be discussed. This study aims to enhance the accuracy of deep geophysical detections, and provide examples for the integration of deep geophysical detection techniques and regional geophysical detection with high accuracy. The MT observation experiments located in the northeast edge of Tibet Plateau, the west Qinling Orogen, and the mountain areas with crystallized rocks in Fujian province has accomplished. The result shows that, in these areas with typical geological structures, though difficulties exist during the acquisition, and the noise is very strong in some areas, it is still possible to acquire the MT data with high quality and consequently get a reliable model of the underground electrical resistivity by choosing proper technique for field observation and taking discreet computation. The results from this experimental project will become important technical support and insurance for the realization of the scientific objectives of the "experiment and integration of deep detection technology" project.
By the observation of geophysical field parameters such as seismic velocity, density, magnetism, and electrical conductivity, we have obtained the physical properties and structure features of the earth's crust and upper mantle. Thus scientific evidence further facilitates the understanding of the earth's interior status, the process and mechanism of the movement of crust, and other scientific subjects. Furthermore, such useful information can also lead to the exploration of large-scale mineral deposits. As a primary geophysical method for the detection of the electrical structure of the earth's crust and mantle, magnetotelluric exploration has been widely adopted both in China and foreign countries, and numerous significant research results have been acquired. The seismic and magnetotelluric methods are recognized as two of the dominant methods on the study of the structure of the earth's crust and mantle. They have been proved to be very effective in solving worldwide continent dynamic problems by numerous application cases. However, because the natural electromagnetic field tend to be affected by noises, it is difficult for the MT method to acquire ideal data with high signal-to-noise ratio in the mineral-enriched areas with strong noises. At the same time, the technique of constraining inversion and joint interpretation for seismic and MT data is still not ready for utilization. All the reasons mentioned above limit the accuracy of the process and interpretation of MT data. The project of "experiment and integration of deep detection technology" belongs to the "SinoProbe" project. It takes different areas with both complicated geological conditions and different situation of man-made noises, like the Tibet plateau, the western orogen, and the mountain areas with crystallized rocks in the south china, as target area to study the integration of geophysical techniques for detailed deep detection by utilizing the seismic and MT methods. The electrical structures of these areas are given from the results of the experimental profiles. The subject, which is named "the MT observation experiments and the study of electrical structure of the earth's crust and mantle", will focus on the study of suitable MT acquisition and computation techniques for different noise environment and geological conditions. The constraining inversion and joint interpretation of seismic and MT data will also be discussed. This study aims to enhance the accuracy of deep geophysical detections, and provide examples for the integration of deep geophysical detection techniques and regional geophysical detection with high accuracy. The MT observation experiments located in the northeast edge of Tibet Plateau, the west Qinling Orogen, and the mountain areas with crystallized rocks in Fujian province has accomplished. The result shows that, in these areas with typical geological structures, though difficulties exist during the acquisition, and the noise is very strong in some areas, it is still possible to acquire the MT data with high quality and consequently get a reliable model of the underground electrical resistivity by choosing proper technique for field observation and taking discreet computation. The results from this experimental project will become important technical support and insurance for the realization of the scientific objectives of the "experiment and integration of deep detection technology" project.
引文
陈乐寿,王光锷.1990.大地电磁测深法.北京:地质出版社.
董树文,李廷栋.2009.Sinoprobe——中国深部探测实验.地质学报,83(7):895～909.
郭新峰,张元丑,程庆云,等.1990.青藏高原亚东—格尔木地学断面岩石圈电性研究.中国地质科学院院报,21:191～202.
黄怀曾,吴功建,朱英,等.1994.岩石圈动力学研究.北京:地质出版社,3～5.
金胜,叶高峰,魏文博,邓明,景建恩.2007.青藏高原西缘壳幔电性结构与断裂构造:札达-泉水湖剖面大地电磁探测提供的依据.地球科学,32(4):474～480.
孔祥儒,王谦身,熊绍柏.1996.西藏高原西部综合地球物理与岩石圈结构研究.中国科学(D辑),26(4):308～315.
孙洁,晋文光,白登海,等.2003.青藏高原东缘地壳、上地幔电性结构探测及其构造意义.中国科学(D辑),33:173～181.
谭捍东,魏文博,Unsworth M,等.2004.西藏高原南部雅鲁藏布江缝合带地区地壳电性结构研究.地球物理学报,47(4):685～691.
魏文博,陈乐寿,谭捍东,等.1997.西藏高原大地电磁深探测——亚东—巴木措沿线地区壳幔电性结构.现代地质,11(3):366～374.
魏文博,金胜,叶高峰,等.2006.西藏高原中、北部断裂构造特征:I NDEPTH(Ⅲ)——MT观测提供的依据.地球科学—中国地质大学学报,31(2):257～265.
叶高峰,金胜,魏文博,等.2007.西藏高原中南部地壳与上地幔导电性结构.地球科学,32(4):491～499.
朱仁学,胡祥云.1995.格尔木—额济纳旗地学断面岩石圈电性结构研究.地球物理学报,38(增刊II):46～57.
DeGroot H C,Constable S C.1990.Occam’s inversion to generatesmooth,two-di mensional models from magnetotelluric data.Geophysics,55:1613～1624.
Egbert G,Booker J R.1986.Robust esti mation of geomagnetictransfer functions.Geophys.J.R.Astr.Soc.,87:173～194.
Frost B R,Fyfe W S,Tazaki K,Chan T.1989.Grain-boundarygraphite in rocks andi mplications for high electrical conductivityin the lower crust.Nature,340:134～136.
Gary W M,Jones A G.2001.Mutisite mutifrequecy tensordecomposition of magnetotelluric data.Geophysics,66(1):158～173.
Groom R W,Bailey R C.1995.Analyticinvestigations of the effectsof near-surface three-di mention galvanic scatterers on MTtensor decompositions.Geophysics,56(4):496～518.
Jones A G,Ferguson I J.2001.The electric Moho.Nature,409:331～33.
Marquis G,Hyndman R D.1992.Geophysical support for aqueousfluids in the deep crust:seismic and electrical relationships.Geophysical Journal International,110:91.
Nover G,Heikamp S,Meurer H J,Freund D.1998.In-situelectrocal conductivity and permeability of mid-crustal rocksfromthe KTB drilling:consequences for high conductive layersin the Earth crust.Surv.Geophys.,19:73～85.
Wei W,Unsworth M,Jones A,et al.2001.Detection ofwidespread fluids in the Tibetan crust by magnetotelluricstudies.Science,292:716～718.
Yardley B,Valley J.1997.The petrologic case for a drylower crust.J.Geophys.Res.,102:12173.
董树文,李廷栋.2009.Sinoprobe——中国深部探测实验.地质学报,83(7):895～909.
郭新峰,张元丑,程庆云,等.1990.青藏高原亚东—格尔木地学断面岩石圈电性研究.中国地质科学院院报,21:191～202.
黄怀曾,吴功建,朱英,等.1994.岩石圈动力学研究.北京:地质出版社,3～5.
金胜,叶高峰,魏文博,邓明,景建恩.2007.青藏高原西缘壳幔电性结构与断裂构造:札达-泉水湖剖面大地电磁探测提供的依据.地球科学,32(4):474～480.
孔祥儒,王谦身,熊绍柏.1996.西藏高原西部综合地球物理与岩石圈结构研究.中国科学(D辑),26(4):308～315.
孙洁,晋文光,白登海,等.2003.青藏高原东缘地壳、上地幔电性结构探测及其构造意义.中国科学(D辑),33:173～181.
谭捍东,魏文博,Unsworth M,等.2004.西藏高原南部雅鲁藏布江缝合带地区地壳电性结构研究.地球物理学报,47(4):685～691.
魏文博,陈乐寿,谭捍东,等.1997.西藏高原大地电磁深探测——亚东—巴木措沿线地区壳幔电性结构.现代地质,11(3):366～374.
魏文博,金胜,叶高峰,等.2006.西藏高原中、北部断裂构造特征:I NDEPTH(Ⅲ)——MT观测提供的依据.地球科学—中国地质大学学报,31(2):257～265.
叶高峰,金胜,魏文博,等.2007.西藏高原中南部地壳与上地幔导电性结构.地球科学,32(4):491～499.
朱仁学,胡祥云.1995.格尔木—额济纳旗地学断面岩石圈电性结构研究.地球物理学报,38(增刊II):46～57.
DeGroot H C,Constable S C.1990.Occam’s inversion to generatesmooth,two-di mensional models from magnetotelluric data.Geophysics,55:1613～1624.
Egbert G,Booker J R.1986.Robust esti mation of geomagnetictransfer functions.Geophys.J.R.Astr.Soc.,87:173～194.
Frost B R,Fyfe W S,Tazaki K,Chan T.1989.Grain-boundarygraphite in rocks andi mplications for high electrical conductivityin the lower crust.Nature,340:134～136.
Gary W M,Jones A G.2001.Mutisite mutifrequecy tensordecomposition of magnetotelluric data.Geophysics,66(1):158～173.
Groom R W,Bailey R C.1995.Analyticinvestigations of the effectsof near-surface three-di mention galvanic scatterers on MTtensor decompositions.Geophysics,56(4):496～518.
Jones A G,Ferguson I J.2001.The electric Moho.Nature,409:331～33.
Marquis G,Hyndman R D.1992.Geophysical support for aqueousfluids in the deep crust:seismic and electrical relationships.Geophysical Journal International,110:91.
Nover G,Heikamp S,Meurer H J,Freund D.1998.In-situelectrocal conductivity and permeability of mid-crustal rocksfromthe KTB drilling:consequences for high conductive layersin the Earth crust.Surv.Geophys.,19:73～85.
Wei W,Unsworth M,Jones A,et al.2001.Detection ofwidespread fluids in the Tibetan crust by magnetotelluricstudies.Science,292:716～718.
Yardley B,Valley J.1997.The petrologic case for a drylower crust.J.Geophys.Res.,102:12173.
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