利用接收函数和大地电磁数据联合反演南迦巴瓦构造结中部地区壳幔结构
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摘要
利用2010年布设在西藏南迦巴瓦构造结的郎嘎、崩嘎、直白和拉格四个宽频地震台所观测到的近5个月的地震记录,采用时间域迭代反褶积技术处理得到接收函数,通过筛选多条相近震中距和反方位角的高质量接收函数求取其叠加平均.对大地电磁数据做Rhoplus分析处理得到视电阻率和相位曲线.利用单台接收函数和相同位置的大地电磁视电阻率和相位联合反演地下一维壳幔结构.联合反演采用遗传算法,并通过权衡图分析大地电磁和地震数据的兼容性.理论值和实测值的对比显示两种数据能同时得到较好拟合.联合反演结果表明:(1)中上地壳为9km至14km厚的高阻高速层覆盖于低阻低速层之上的结构,中地壳低阻低速层可能与深部流体和局部熔融共同作用有关.(2)下地壳存在最厚达20km的高导的壳幔过渡层,波速在4km/s左右;上地幔约130km至150km以下存在软流圈.(3)上地壳的高阻高速层解释为多雄拉组混合岩化角闪岩相变质岩,而直白台所显示的低阻低速层与高压麻粒岩的少量部分熔融有关,可能源于壳幔过渡带镁铁质岩石的相变或更深处幔源岩浆底侵作用的产物.
Using tele-seismograms from four stations(Langga station,Bengga station,Zhibai station and Lage station) for about five months in the central Namche Barwa,eastern Himalayan syntaxis in Tibet,we calculated receiver functions by time-domain iterative deconvolution technique and selected high-quality receiver functions with similar epicentral distances and back azimuths and then stacked them.Magnetotelluric apparent resistivity and phase curves are obtained by Rhoplus analysis of Berdichevskiy invariant of impedance tensors.The average receiver function and apparent resistivity and phase data from the same station are jointly inverted for one-dimensional Earth to infer lithospheric structure.Using genetic algorithm,we analyzed the compatibility between the magnetotelluric data and the seismic data by trade-off plots.The comparison of predicted data and measured data manifests that they coincide on both data sets.The results demonstrate:(1) In the mid-upper crust,a high resistivity,high velocity layer(9~14 km thickness) overlays a low resistivity and low velocity layer which may be related to aqueous fluids and partial melts.(2) There exists a highly conductive crust-mantle transition layer(thickness <20 km) with the S wave velocity of ~4 km/s in the lower crust,and also exists the lithosphere-asthenosphere boundary deeper than 130~150 km in the upper mantle.(3) A possible interpretation about the high resistivity and high velocity layer in the upper crust is the migmatitic amphibolite facies(Duoxiongla Formation),while the low resistivity,low velocity layer beneath the Zhibai station is associated with partial melting.And high-pressure granulite facies may originate from petrological transformation of mafic rocks in the crust-mantle transition layer or from mantle-derived magma underplating.
Using tele-seismograms from four stations(Langga station,Bengga station,Zhibai station and Lage station) for about five months in the central Namche Barwa,eastern Himalayan syntaxis in Tibet,we calculated receiver functions by time-domain iterative deconvolution technique and selected high-quality receiver functions with similar epicentral distances and back azimuths and then stacked them.Magnetotelluric apparent resistivity and phase curves are obtained by Rhoplus analysis of Berdichevskiy invariant of impedance tensors.The average receiver function and apparent resistivity and phase data from the same station are jointly inverted for one-dimensional Earth to infer lithospheric structure.Using genetic algorithm,we analyzed the compatibility between the magnetotelluric data and the seismic data by trade-off plots.The comparison of predicted data and measured data manifests that they coincide on both data sets.The results demonstrate:(1) In the mid-upper crust,a high resistivity,high velocity layer(9~14 km thickness) overlays a low resistivity and low velocity layer which may be related to aqueous fluids and partial melts.(2) There exists a highly conductive crust-mantle transition layer(thickness <20 km) with the S wave velocity of ~4 km/s in the lower crust,and also exists the lithosphere-asthenosphere boundary deeper than 130~150 km in the upper mantle.(3) A possible interpretation about the high resistivity and high velocity layer in the upper crust is the migmatitic amphibolite facies(Duoxiongla Formation),while the low resistivity,low velocity layer beneath the Zhibai station is associated with partial melting.And high-pressure granulite facies may originate from petrological transformation of mafic rocks in the crust-mantle transition layer or from mantle-derived magma underplating.
引文
[1]Gallardo L A,Meju M A.Characterization of heterogeneousnear-surface materials by joint 2Dinversion of DC resistivityand seismic data.Geophys.Res.Lett.,2003,30(13):1658.
[2]Gallardo L A,Meju M A.Joint two-dimensional DCresistivity and seismic travel time inversion with cross-gradients constraints.J.Geophys.Res.,2004,109(B3):B03311.
[3]Gallardo L A,Meju M A.Joint two-dimensional cross-gradient imaging of magnetotelluric and seismic traveltimedata for structural and lithological classification.Geophys.J.Int.,2007,169(3):1261-1272.
[4]Heincke B,Jegen M,Hobbs R.Joint inversion of MT,gravity and seismic data applied to sub-basalt imaging.SEGTech.Prog.Expand.Abstracts,2006,25(1):784-789.
[5]Colombo D,Stefano M D.Geophysical modeling viasimultaneous joint inversion of seismic,gravity,andelectromagnetic data:application to prestack depth imaging.Leading Edge,2007,26(3):326-331.
[6]Moorkamp M,Heincke B,Jegen M,et al.A framework for3-D joint inversion of MT,gravity and seismic refractiondata.Geophys.J.Int.,2011,184(1):477-493.
[7]杨辉,王家林,吴健生等.大地电磁与地震资料仿真退火约束联合反演.地球物理学报,2002,45(5):723-734.Yang H,Wang J L,Wu J S,et al.Constrained jointinversion of magnetotelluric and seismic data using simulatedannealing algorithm.Chinese J.Geophys.(in Chinese),2002,45(5):723-734.
[8]于鹏,戴明刚,王家林等.电阻率和速度随机分布的MT与地震联合反演.地球物理学报,2009,52(4):1089-1097.Yu P,Dai M G,Wang J L,et al.Joint inversion ofmagnetotelluric and seismic data based on random resistivityand velocity distributions.Chinese J.Geophys.(in Chinese),2009,52(4):1089-1097.
[9]陈高,于鹏,陈晓等.改进的大地电磁与地震资料联合反演方法在黔中隆起区的适用性研究.石油物探,2010,49(2):158-163.Chen G,Yu P,Chen X,et al.Adaptability research onimproved joint inversion method of magnetotelluric andseismic data in middle Guizhou Uplift.Geophys.Pros.forPetroleum(in Chinese),2010,49(2):158-163,doi:10.3969/j.issn.1000-1441.2010.02.009.
[10]陈晓,于鹏,张罗磊等.大地电磁与地震正则化同步联合反演.地震地质,2010,32(3):402-408.Chen X,Yu P,Zhang L L,et al.Regularized synchronousjoint inversion of MT and seismic data.Seismology andGeology(in Chinese),2010,32(3):402-408.
[11]陈晓,于鹏,张罗磊等.地震与大地电磁测深数据的自适应正则化同步联合反演.地球物理学报,2011,54(10):2673-2681.Chen X,Yu P,Zhang L L,et al.Adaptive regularizedsynchronous joint inversion of MT and seismic data.ChineseJ.Geophys.(in Chinese),2011,54(10):2673-2681.
[12]彭淼,谭捍东,姜枚.远震接收函数和大地电磁数据联合反演在南迦巴瓦东构造结的应用.第十届中国国际地球电磁学术讨论会.扩展摘要,2011:4-6.Peng M,Tan H D,Jiang M.Joint inversion of receiverfunctions and magnetotelluric data:Application to data fromcentral Namche Barwa,eastern Himalayan syntaxis.10thChina International Geo-Electromagnetic Workshop.ExpandedAbstracts,2011:4-6.
[13]Moorkamp M,Jones A G,Eaton D W.Joint inversion ofteleseismic receiver functions and magnetotelluric data using agenetic algorithm:Are seismic velocities and electricalconductivities compatible?Geophys.Res.Lett.,2007,34(6):L16311,doi:10.1029/2007GL030519.
[14]Moorkamp M,Jones A G,Fishwick S.Joint inversion ofreceiver functions,surface wave dispersion and magnetotelluricdata.J.Geophys.Res.,2010,115(B4):B04318,doi:10.1029/2009JB006369.
[15]Zevallos I,Assumpca珘o M,Padilha A L.Inversion ofteleseismic receiver function and magnetotelluric sounding todetermine basement depth in the ParanáBasin,SE Brazil.Journal of Applied Geophysics,2009,68(2):231-242.
[16]Roux E,Moorkamp M,Jones A G,et al.Joint inversion oflong-period magnetotelluric data and surface-wave dispersioncurves for anisotropic structure:Application to data fromCentral Germany.Geophys.Res.Lett.,2011,38(5):L05304,doi:10.1029/2010GL046358.
[17]Kozlovskaya E,Hjelt S E.Modeling of elastic and electricalproperties of solid-liquid rock system with fractal microstructure.Physics and Chemistry of the Earth,2000,25(2):195-200.
[18]许志琴,蔡志慧,张泽明等.喜马拉雅东构造结———南迦巴瓦构造及组构运动学.岩石学报,2008,24(7):1463-1476.Xu Z Q,Cai Z H,Zhang Z M,et al.Tectonics and fabrickinematics of the Namche Barwa terrane,Eastern HimalayanSyntaxis.Acta Petrologica Sinica(in Chinese),2008,24(7):1463-1476.
[19]张泽明,郑来林,王金丽等.东喜马拉雅构造结南迦巴瓦岩群中的石榴辉石岩———印度大陆向欧亚板块之下俯冲至80～100km深度的证据.地质通报,2007,26(1):1-12.Zhang Z M,Zheng L L,Wang J L,et al.Garnet pyroxenitein the Namjagbarwa Group-complex in the eastern Himalayantectonic syntaxis,Tibet,China:Evidence for subduction ofthe Indian continent beneath the Eurasian plate at 80～100km depth.Geological Bulletin of China(in Chinese),2007,26(1):1-12.
[20]许志琴,杨经绥,李海兵等.青藏高原与大陆动力学———地体拼合、碰撞造山及高原隆升的深部驱动力.中国地质,2006,33(2):221-238.Xu Z Q,Yang J S,Li H B,et al.The Qinghai-Tibet plateauand continental dynamics:A review on terrain tectonics,collisional orogenesis,and processes and mechanisms for therise of the plateau.Geology in China(in Chinese),2006,33(2):221-238.
[21]Park S K,Livelybrook D W.Quantitative interpretation ofrotation in variant parameters in magnetotellurics.Geophysics,1989,54(11):1483-1490.
[22]谭捍东,齐伟威,郎静.大地电磁法中的RHOPLUS理论及其应用研究.物探与化探,2004,28(6):532-535.Tan H D,Qi W W,Lang J.The RHOPLUS theory inmagnetotelluric method and its application.Geophysical andGeochemical Exploration(in Chinese),2004,28(6):532-535.
[23]Langston C A.Structure under Mount Rainier,Washington,inferred from teleseismic body waves.J.Geophys.Res.,1979,84(B9):4749-4762.
[24]Ligorria J P,Ammon C J.Iterative deconvolution andreceiver-function estimation.Bull.Seismol.Soc.Am.,1999,89(5):1395-1400.
[25]Deb K,Pratap A,Agarwal S,et al.A fast and elitistmultiobjective genetic algorithm:NSGA—II.IEEE Trans.Evol.Comput.,2002,6(2):182-197.
[26]谭捍东,魏文博,Martyn Unsworth等.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,2004,47(4):685-690.Tan H D,Wei W B,Martyn Unsworth,et al.Crustalelectrical conductivity structure beneath the Yarlung ZangboJiang suture in the southern Xizang plateau.Chinese J.Geophys.(in Chinese),2004,47(4):685-690.
[27]徐果明,姚华建,朱良保等.中国西部及其邻域地壳上地幔横波速度结构.地球物理学报,2007,50(1):193-208.Xu G M,Yao H J,Zhu L B,et al.Shear wave velocitystructure of the crust and upper mantle in western China andits adjacent area.Chinese J.Geophys.(in Chinese),2007,50(1):193-208.
[28]Chen Y,Badal J,Hu J F.Love and Rayleigh wavetomography of the Qinghai-Tibet Plateau and surroundingAreas.Pure and Applied Geophysics,2010,167(10):1171-1203.
[2]Gallardo L A,Meju M A.Joint two-dimensional DCresistivity and seismic travel time inversion with cross-gradients constraints.J.Geophys.Res.,2004,109(B3):B03311.
[3]Gallardo L A,Meju M A.Joint two-dimensional cross-gradient imaging of magnetotelluric and seismic traveltimedata for structural and lithological classification.Geophys.J.Int.,2007,169(3):1261-1272.
[4]Heincke B,Jegen M,Hobbs R.Joint inversion of MT,gravity and seismic data applied to sub-basalt imaging.SEGTech.Prog.Expand.Abstracts,2006,25(1):784-789.
[5]Colombo D,Stefano M D.Geophysical modeling viasimultaneous joint inversion of seismic,gravity,andelectromagnetic data:application to prestack depth imaging.Leading Edge,2007,26(3):326-331.
[6]Moorkamp M,Heincke B,Jegen M,et al.A framework for3-D joint inversion of MT,gravity and seismic refractiondata.Geophys.J.Int.,2011,184(1):477-493.
[7]杨辉,王家林,吴健生等.大地电磁与地震资料仿真退火约束联合反演.地球物理学报,2002,45(5):723-734.Yang H,Wang J L,Wu J S,et al.Constrained jointinversion of magnetotelluric and seismic data using simulatedannealing algorithm.Chinese J.Geophys.(in Chinese),2002,45(5):723-734.
[8]于鹏,戴明刚,王家林等.电阻率和速度随机分布的MT与地震联合反演.地球物理学报,2009,52(4):1089-1097.Yu P,Dai M G,Wang J L,et al.Joint inversion ofmagnetotelluric and seismic data based on random resistivityand velocity distributions.Chinese J.Geophys.(in Chinese),2009,52(4):1089-1097.
[9]陈高,于鹏,陈晓等.改进的大地电磁与地震资料联合反演方法在黔中隆起区的适用性研究.石油物探,2010,49(2):158-163.Chen G,Yu P,Chen X,et al.Adaptability research onimproved joint inversion method of magnetotelluric andseismic data in middle Guizhou Uplift.Geophys.Pros.forPetroleum(in Chinese),2010,49(2):158-163,doi:10.3969/j.issn.1000-1441.2010.02.009.
[10]陈晓,于鹏,张罗磊等.大地电磁与地震正则化同步联合反演.地震地质,2010,32(3):402-408.Chen X,Yu P,Zhang L L,et al.Regularized synchronousjoint inversion of MT and seismic data.Seismology andGeology(in Chinese),2010,32(3):402-408.
[11]陈晓,于鹏,张罗磊等.地震与大地电磁测深数据的自适应正则化同步联合反演.地球物理学报,2011,54(10):2673-2681.Chen X,Yu P,Zhang L L,et al.Adaptive regularizedsynchronous joint inversion of MT and seismic data.ChineseJ.Geophys.(in Chinese),2011,54(10):2673-2681.
[12]彭淼,谭捍东,姜枚.远震接收函数和大地电磁数据联合反演在南迦巴瓦东构造结的应用.第十届中国国际地球电磁学术讨论会.扩展摘要,2011:4-6.Peng M,Tan H D,Jiang M.Joint inversion of receiverfunctions and magnetotelluric data:Application to data fromcentral Namche Barwa,eastern Himalayan syntaxis.10thChina International Geo-Electromagnetic Workshop.ExpandedAbstracts,2011:4-6.
[13]Moorkamp M,Jones A G,Eaton D W.Joint inversion ofteleseismic receiver functions and magnetotelluric data using agenetic algorithm:Are seismic velocities and electricalconductivities compatible?Geophys.Res.Lett.,2007,34(6):L16311,doi:10.1029/2007GL030519.
[14]Moorkamp M,Jones A G,Fishwick S.Joint inversion ofreceiver functions,surface wave dispersion and magnetotelluricdata.J.Geophys.Res.,2010,115(B4):B04318,doi:10.1029/2009JB006369.
[15]Zevallos I,Assumpca珘o M,Padilha A L.Inversion ofteleseismic receiver function and magnetotelluric sounding todetermine basement depth in the ParanáBasin,SE Brazil.Journal of Applied Geophysics,2009,68(2):231-242.
[16]Roux E,Moorkamp M,Jones A G,et al.Joint inversion oflong-period magnetotelluric data and surface-wave dispersioncurves for anisotropic structure:Application to data fromCentral Germany.Geophys.Res.Lett.,2011,38(5):L05304,doi:10.1029/2010GL046358.
[17]Kozlovskaya E,Hjelt S E.Modeling of elastic and electricalproperties of solid-liquid rock system with fractal microstructure.Physics and Chemistry of the Earth,2000,25(2):195-200.
[18]许志琴,蔡志慧,张泽明等.喜马拉雅东构造结———南迦巴瓦构造及组构运动学.岩石学报,2008,24(7):1463-1476.Xu Z Q,Cai Z H,Zhang Z M,et al.Tectonics and fabrickinematics of the Namche Barwa terrane,Eastern HimalayanSyntaxis.Acta Petrologica Sinica(in Chinese),2008,24(7):1463-1476.
[19]张泽明,郑来林,王金丽等.东喜马拉雅构造结南迦巴瓦岩群中的石榴辉石岩———印度大陆向欧亚板块之下俯冲至80～100km深度的证据.地质通报,2007,26(1):1-12.Zhang Z M,Zheng L L,Wang J L,et al.Garnet pyroxenitein the Namjagbarwa Group-complex in the eastern Himalayantectonic syntaxis,Tibet,China:Evidence for subduction ofthe Indian continent beneath the Eurasian plate at 80～100km depth.Geological Bulletin of China(in Chinese),2007,26(1):1-12.
[20]许志琴,杨经绥,李海兵等.青藏高原与大陆动力学———地体拼合、碰撞造山及高原隆升的深部驱动力.中国地质,2006,33(2):221-238.Xu Z Q,Yang J S,Li H B,et al.The Qinghai-Tibet plateauand continental dynamics:A review on terrain tectonics,collisional orogenesis,and processes and mechanisms for therise of the plateau.Geology in China(in Chinese),2006,33(2):221-238.
[21]Park S K,Livelybrook D W.Quantitative interpretation ofrotation in variant parameters in magnetotellurics.Geophysics,1989,54(11):1483-1490.
[22]谭捍东,齐伟威,郎静.大地电磁法中的RHOPLUS理论及其应用研究.物探与化探,2004,28(6):532-535.Tan H D,Qi W W,Lang J.The RHOPLUS theory inmagnetotelluric method and its application.Geophysical andGeochemical Exploration(in Chinese),2004,28(6):532-535.
[23]Langston C A.Structure under Mount Rainier,Washington,inferred from teleseismic body waves.J.Geophys.Res.,1979,84(B9):4749-4762.
[24]Ligorria J P,Ammon C J.Iterative deconvolution andreceiver-function estimation.Bull.Seismol.Soc.Am.,1999,89(5):1395-1400.
[25]Deb K,Pratap A,Agarwal S,et al.A fast and elitistmultiobjective genetic algorithm:NSGA—II.IEEE Trans.Evol.Comput.,2002,6(2):182-197.
[26]谭捍东,魏文博,Martyn Unsworth等.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,2004,47(4):685-690.Tan H D,Wei W B,Martyn Unsworth,et al.Crustalelectrical conductivity structure beneath the Yarlung ZangboJiang suture in the southern Xizang plateau.Chinese J.Geophys.(in Chinese),2004,47(4):685-690.
[27]徐果明,姚华建,朱良保等.中国西部及其邻域地壳上地幔横波速度结构.地球物理学报,2007,50(1):193-208.Xu G M,Yao H J,Zhu L B,et al.Shear wave velocitystructure of the crust and upper mantle in western China andits adjacent area.Chinese J.Geophys.(in Chinese),2007,50(1):193-208.
[28]Chen Y,Badal J,Hu J F.Love and Rayleigh wavetomography of the Qinghai-Tibet Plateau and surroundingAreas.Pure and Applied Geophysics,2010,167(10):1171-1203.
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