华北克拉通泊松比与地壳厚度的关系及其大地构造意义
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摘要
华北克拉通破坏和岩石圈减薄已成为我国乃至国际地学界研究的热点之一。本文作者对许卫卫和郑天愉(2005)采用接收函数方法测量渤海湾西北盆岭地区58个宽频地震台站下面地壳厚度和地壳泊松比的资料进行了详细的分析研究。在冀东北、辽西以及石家庄附近的南太行山地区地壳泊松比随地壳厚度增加呈非线性骤然陡降,说明在这些地区中新生代地壳减薄作用主要集中于长英质的中上地壳。在保定—大同和官厅水库—张家口—张北地区,地壳泊松比随地壳厚度增加作缓慢地线性减小,说明由玄武岩浆底侵作用造成的地壳泊松比增加抵消了一部分由长英质中上地壳减薄造成的泊松比减小。所以,在中新生代华北克拉通地壳减薄过程中,上地幔部分熔融及玄武岩浆底侵作用主要集中在保定—大同和官厅水库—张家口—张北等冀西北地区。
Data of the crustal thickness and Poisson's ratio from 58 broadband seismic stations in the North China Craton,measured by Xu and Zheng(2005,Chinese Journal of Geophysics,48,1077～1084) using the techniques of teleseismic receiver functions,have been carefully examined.Two types of correlation between the crustal thickness(H) and Poisson's ratio(ν) have been observed: with decreasing H,ν increases gently and linearly in the Baoding-Datong and Guanting-Zhangjiakou-Zhangbei regions,while increasing abruptly and nonlinearly in the rest of the block(e.g.,Northeastern Hebei province and the southern Taihangshan area near Shijiazhuang).The linear correlation is interpreted as due to the summed,opposing contribution of tectonic thinning of felsic crust and the addition of mafic rocks crystallized from underplated magmas to the bulk crustal ν.The abrupt increase of ν with decreasing H suggests that much larger thinning strains have taken place in the felsic upper and middle crust than in the mafic lower crust during Mesozoic-Cenozoic tectonic extension.It is further inferred that basaltic underplating has been localized mainly in the Zhangjiakou and adjacent regions.
Data of the crustal thickness and Poisson's ratio from 58 broadband seismic stations in the North China Craton,measured by Xu and Zheng(2005,Chinese Journal of Geophysics,48,1077～1084) using the techniques of teleseismic receiver functions,have been carefully examined.Two types of correlation between the crustal thickness(H) and Poisson's ratio(ν) have been observed: with decreasing H,ν increases gently and linearly in the Baoding-Datong and Guanting-Zhangjiakou-Zhangbei regions,while increasing abruptly and nonlinearly in the rest of the block(e.g.,Northeastern Hebei province and the southern Taihangshan area near Shijiazhuang).The linear correlation is interpreted as due to the summed,opposing contribution of tectonic thinning of felsic crust and the addition of mafic rocks crystallized from underplated magmas to the bulk crustal ν.The abrupt increase of ν with decreasing H suggests that much larger thinning strains have taken place in the felsic upper and middle crust than in the mafic lower crust during Mesozoic-Cenozoic tectonic extension.It is further inferred that basaltic underplating has been localized mainly in the Zhangjiakou and adjacent regions.
引文
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Gao S,Zhang B R,Jin Z M,Kern H,Luo T C,Zhao Z D.1998.Howmafic is the lower continental crust?Earth and PlanetaryScience Letters,161(1～4):101～117.
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Ji S C,Saruwatari K,Mainprice D,Wirch R,Xu Z Q,Xia B.2003.Microstructures,petrofabrics and seismic properties ofultrahigh-pressure eclogites from Sulu region,China:I mplications for rheology of subducted continental crust andorigin of mantle reflections.Tectonophysics,370:49～76.
Lakes R S.1987.Foam structures with a negative Poisson’s ratio.Science,235:1038～1040.
Mavko G,Mukerji T,Dyorkin J.1998.The Rock Physics Handbook:Tools for Seismic Analysis of Porous Media.New York:Cambridge University Press,339.
Mishra O P,Zhao D P.2003.Crack density,saturation rate andporosity at the2001Bhuj,India,earthquake hypocenter:Afluid-driven earthquake?Earth and Planetary Science Letters,212:393～405.
Wang Z C,Ji S C.1999.Deformation of silicate garnets:brittle-ductile transition and its geological i mplications.CanadianJournal of Mineralogy,37:525～541.
Wang Z C,Ji S C.2001.Elasticity of six polycrystalline silicategarnets at pressure up to3.0GPa.American Mineralogist,86:1209～1218.
Wilkens R,Si mmons G,Caruso L.1984.The ratio Vp/Vs as adiscri minant of composition for siliceous li mestones.Geophysics,49:1850～1860.
Zandt G and Ammon C J.1995.Continental crust compositionconstrained by measurements of crustal Poisson’s ratio.Nature,374:152～154.
许卫卫,郑天愉.2005.渤海湾盆地北西盆山边界地区泊松比分布.地球物理学报,48(5):1077～108.
Christensen N I.1996.Poisson’s ratio and crustal seismology.Journal of Geophysical Research,101:3139～3156.
Gao S,Zhang B R,Jin Z M,Kern H,Luo T C,Zhao Z D.1998.Howmafic is the lower continental crust?Earth and PlanetaryScience Letters,161(1～4):101～117.
Gercek H.2007.Poisson’s ratio values for rocks.InternationalJournal of Rock Mechanics and Mining Sciences,44:1～13.
Holbrook W S,Gajewski P,Krammer A,Prodehl C.1988.Aninterpretation of wide-angle compressional and shear wave datain southwest Germany:Poisson’s ratio and petrologicali mplications.Journal of Geophysical Research,93:12081～12106.
Ji S C,Salisbury M H.1993.Shear-wave velocities,anisotropy and splittingin the high grade mylonites.Tectonophysics,221:453～473.
Ji S C,Wang Q,Xia B.2002.Handbook of Seismic Properties ofMinerals,Rocks and Ores.Montreal:Polytechnic InternationalPress,630.
Ji S C,Xia B.2002.Rheology of Polyphase Earth Materials.Montreal:Polytechnic International Press,260.
Ji S C.2008.Deformation Mechanisms,Rheology,and SeismicProperities of Rocks,Beijing:Geological Publishing House,539.
Ji S C,Saruwatari K,Mainprice D,Wirch R,Xu Z Q,Xia B.2003.Microstructures,petrofabrics and seismic properties ofultrahigh-pressure eclogites from Sulu region,China:I mplications for rheology of subducted continental crust andorigin of mantle reflections.Tectonophysics,370:49～76.
Lakes R S.1987.Foam structures with a negative Poisson’s ratio.Science,235:1038～1040.
Mavko G,Mukerji T,Dyorkin J.1998.The Rock Physics Handbook:Tools for Seismic Analysis of Porous Media.New York:Cambridge University Press,339.
Mishra O P,Zhao D P.2003.Crack density,saturation rate andporosity at the2001Bhuj,India,earthquake hypocenter:Afluid-driven earthquake?Earth and Planetary Science Letters,212:393～405.
Wang Z C,Ji S C.1999.Deformation of silicate garnets:brittle-ductile transition and its geological i mplications.CanadianJournal of Mineralogy,37:525～541.
Wang Z C,Ji S C.2001.Elasticity of six polycrystalline silicategarnets at pressure up to3.0GPa.American Mineralogist,86:1209～1218.
Wilkens R,Si mmons G,Caruso L.1984.The ratio Vp/Vs as adiscri minant of composition for siliceous li mestones.Geophysics,49:1850～1860.
Zandt G and Ammon C J.1995.Continental crust compositionconstrained by measurements of crustal Poisson’s ratio.Nature,374:152～154.
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