中国大陆科学钻探主孔100～2000m岩石弹性波速度:对地震深反射的约束
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摘要
在常温常压条件对中国大陆科学钻CCSD主孔岩心的700样品进行了弹性波速度测量,并建立了主孔2000m的波速(Vp和Vs)连续剖面,为检验地球物理模型的合理解释提供了岩石物理学方面的宝贵资料。主孔中新鲜榴辉岩纵波速度(Vp)最大(7.86km/s),正副片麻岩波速最小,又分别为5.53km/s和5.71km/s,榴辉岩的波速随着退变质作用的增强而明显减小。主孔2000m总平均Vp速度为6.2km/s,它与地球物理探测方法获得的大别-苏鲁造山带上地壳具有6.2-6.3km/s 高速层结论是一致的。大部分岩石具有明显地震波各向异性。水饱和度使岩石纵波(Vp)速度和剪切波速度(Vs)分别增加19％和6％,而使Vp的各向异性降低3％-4％。不同岩性界面的反射系数(Rc)是产生地震反射的主要原因。金红石榴辉岩与片麻岩之间具有很高的反射系数(0.24-0.31)。韧性剪切带中糜棱岩化片麻岩和面理化榴辉岩使岩石各向异性和反射强度明显增加。岩石微裂隙与主孔原位波速变化有密切关系。饱水岩石速度(Vp和Vs)可以代表CCSD主孔原位状态的地震波速度。上述成果为本区地震反射体成因提供了重要的岩石物理性质约束。
The elastic wave velocities of 700 samples from main hole of Chinese Continental Scientific Drilling ( CCSD) have been performed in the conditions of room temperature and pressure. The continuous section of seismic velocities ( VP and Vs ) from 100m to 2000m was constructed, which provides an important petrophysical data for interpretation of geophysical model. Fresh eclogite yields the biggest compressional wave velocity (7. 86km/s) , and gneiss has smaller velocity (5. 53 -5. 71km/s) . Seismic velocity of eclogite significantly decreases with increase of retrogressive metamorphism. Overall average Vp velocity of main hole of 2000m rook is 6. 2km/s which is correspondent to conclusion with high velocity zone (6. 2-6. 3km/s) of the upper crust in Dabie-Sulu orogenic belt inferred from geophysical methods. Most rocks at the mail hole have pronounced seismic anisotropy. The velocity of Vp and Vs with water-saturated rock increases by a factor of 19% and 10% , respectively. Conversely, anisotropy of VP and Vs with water-saturated rock reduces 3% - 4%. Reflective coefficient (Rc ) of different lithological boundaries is main factor producing seismic reflection. The lithological boundary between rutile-bearing eclogite and gneiss has the biggest reflective coefficient (0. 24 - 0. 31). Anisotropy and reflective strength is enhanced by mylonitic gneiss and foliated eclogite in ductile shear zone. Anisotropy and shear wave splitting of gneiss and eclogite are caused by the foliation of rocks, as confirmed by laboratory measurements under simulated in situ condition at high pressure and high temperature. Micro-cracks of rocks is closely related to in situ velocity variation. Velocities ( VP and Vs ) water-saturated rocks may represent in situ seismic velocity at main hole of the CCSD. The measurements of elastic wave velocities give an important constraints on the genesis of seismic reflector for this area.
The elastic wave velocities of 700 samples from main hole of Chinese Continental Scientific Drilling ( CCSD) have been performed in the conditions of room temperature and pressure. The continuous section of seismic velocities ( VP and Vs ) from 100m to 2000m was constructed, which provides an important petrophysical data for interpretation of geophysical model. Fresh eclogite yields the biggest compressional wave velocity (7. 86km/s) , and gneiss has smaller velocity (5. 53 -5. 71km/s) . Seismic velocity of eclogite significantly decreases with increase of retrogressive metamorphism. Overall average Vp velocity of main hole of 2000m rook is 6. 2km/s which is correspondent to conclusion with high velocity zone (6. 2-6. 3km/s) of the upper crust in Dabie-Sulu orogenic belt inferred from geophysical methods. Most rocks at the mail hole have pronounced seismic anisotropy. The velocity of Vp and Vs with water-saturated rock increases by a factor of 19% and 10% , respectively. Conversely, anisotropy of VP and Vs with water-saturated rock reduces 3% - 4%. Reflective coefficient (Rc ) of different lithological boundaries is main factor producing seismic reflection. The lithological boundary between rutile-bearing eclogite and gneiss has the biggest reflective coefficient (0. 24 - 0. 31). Anisotropy and reflective strength is enhanced by mylonitic gneiss and foliated eclogite in ductile shear zone. Anisotropy and shear wave splitting of gneiss and eclogite are caused by the foliation of rocks, as confirmed by laboratory measurements under simulated in situ condition at high pressure and high temperature. Micro-cracks of rocks is closely related to in situ velocity variation. Velocities ( VP and Vs ) water-saturated rocks may represent in situ seismic velocity at main hole of the CCSD. The measurements of elastic wave velocities give an important constraints on the genesis of seismic reflector for this area.
引文
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Chen Y, Jin ZM, Ou XG, Jin SY and Xu HJ. 2004． Deformationfeatures of gneiss and UHP eclogite from ductile shear zone and itsrelation with seismic velocity anisotropy: Evidences from coresamples at depth of 680-1200m of CCSD. Acta Petrologica Sinica,20(1) :97-108 (in Chinese with English abstract)
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Dong Shuwen, Wu Xuanzhi, Gao Rui. 1998． On the crust velocity levelsand dynamics of the Dabie shan orogenic belt. Chinese J. Geophys. , 41(3) : 349-361 (in Chinese with English abstract)
Emmeimman R, Lauterjung L. 1997． The German continental deep drilling program KTB: Overview and major results. J. Geophys. Res. , 102(B8) : 18179-18201
Fountain D M, Boundy T M, Austrheim H. 1994． Eclogite facies Shear zone-deep crustal reflector? Tectonophysics, 232: 411-424
Fountain D M, Hurich C A. Smithson S B. 1984． Seismic reflectivity of mylonile zone in the crust. Geology, 12: 195-198
Gao Sha, Jin Zheming, Jin Shuyan, Xu Ziqin, Dong Shuwen. 1997． Preliminary study on seismic velocities and density of ultrahigh-pressure eclogite from Dabie shan: Implication for composition of deep crust and Moho characsters. Chinese Science Bulletin, 42 (8) : 862-866 (in Chinese)
Gao Shan, Liu Yongsheng. 1999． Deep structures and composition of continental crust. In: Zheng Y-F ed. Chemical Geodynamics. Beijing: Science Press, 168-201 (in Chinese)
Holl A, Althaus E, Lempp C. 1997． The petrophysical behavior of crustal rocks under the influence of fluids. Tectonophysics, 275: 253-260
Huenges E, Erizinger J, Kuck J. 1997． The permeable crust: Geohydraulic properties down to 9101 m depth. J. Geophys. Res. , 102 (B8) : 18255-18266
Jin Zhenmin, Green W H, Zhou Yi. 1994． Melt topology in partially molten peridotite during ductile deformation. Nature, 372: 164-167
Jin Shuyan, Jiao Shuqiang. 1998． Fabric measurements of omphacite from ultrahigh-pressure eclogite and rheological significances. Earth Science, 23(1) : 37-40 (in Chinese with English abstract)
Jin shuyan. 1997． Seismic anisotropy of continental lithosphere and its dynamical significances. In: Zhan Bingxi(ed. ). Modern methods for the lithospheric study. Beijing: Publishing House of Atomic Energy, 79-88 (in Chinese)
Jin Zhenmin, Yu Ridong, Yang Wencai and Ou Xingong. 2003． Mantle-derived xenoliths of peridotite from Pingmingshan, Uonghai County, Jiangsu province and their implications for deep structures. Acta Geologica Sinica, 77(4) :451-462 (in Chinese with English abstract)
Jones K A, Warner M R, Morgan R P. 1996． Coincident normal-incidence and wide-angle reflection from the Moho: evidence for crustal seismic anisotropy. Tectonophysics, 264(1-4) : 205-217
Jones T, Hur A. 1982． Seismic velocity and anisotropy in mylonites and reflectivity of deep crust fault zones. Geology, 10: 260-263
Kern H, Shao Gao, Zhenmin Jin, Popp T, Shuyan Jin. 1999． Petrophysical studies on rocks from the Dabie ultrahigh-pressure (UHP) metamorphic belt, Central China: implications for the composition and delamination of the lower crust. Tectonophysics, 301: 191-215
Kern H, Wenk H B. 1990． Fabric-related velocity anisotropy and shear-wave splitting in rocks from the Santo Rosa mylonite
Berekheemer A. Rauen A, Winter H, Kern H. 1997． Petrophysicalproperties of the 9-km deep crustal section at KTB. J. Geophys.Res. , 102(B8) : 18337-18362
Biot M A. 1956． Theory of propagation of elastic waves in a fluidsaturated porous solid 1． low frequency range. J. Acoustic. Soc.Am. , 28(2) : 168-178
Brich F. 1961． The velocity of compressional waves in rocks to 10 kbars.J. Geophys. Res. , 66: 2199-2224
Chen Y, Jin ZM, Ou XG, Jin SY and Xu HJ. 2004． Deformationfeatures of gneiss and UHP eclogite from ductile shear zone and itsrelation with seismic velocity anisotropy: Evidences from coresamples at depth of 680-1200m of CCSD. Acta Petrologica Sinica,20(1) :97-108 (in Chinese with English abstract)
Christensen N L. 1989． Reflectivity and seismic properties of the deepcontinental crust. J. Geophys. Res. , 94: 17795-17804
Chunyong Wang, Rongsheng zeng, Mooney W D, Hacker B R. 2000． Acrustal model of the ultrahigh-pressure Dabie shan orogenic belt,China, derived from deep seismic refraction profding. J. Geophys,Res. , 105 (B5) : 10857-10869
Dong Shuwen, Wu Xuanzhi, Gao Rui. 1998． On the crust velocity levelsand dynamics of the Dabie shan orogenic belt. Chinese J. Geophys. , 41(3) : 349-361 (in Chinese with English abstract)
Emmeimman R, Lauterjung L. 1997． The German continental deep drilling program KTB: Overview and major results. J. Geophys. Res. , 102(B8) : 18179-18201
Fountain D M, Boundy T M, Austrheim H. 1994． Eclogite facies Shear zone-deep crustal reflector? Tectonophysics, 232: 411-424
Fountain D M, Hurich C A. Smithson S B. 1984． Seismic reflectivity of mylonile zone in the crust. Geology, 12: 195-198
Gao Sha, Jin Zheming, Jin Shuyan, Xu Ziqin, Dong Shuwen. 1997． Preliminary study on seismic velocities and density of ultrahigh-pressure eclogite from Dabie shan: Implication for composition of deep crust and Moho characsters. Chinese Science Bulletin, 42 (8) : 862-866 (in Chinese)
Gao Shan, Liu Yongsheng. 1999． Deep structures and composition of continental crust. In: Zheng Y-F ed. Chemical Geodynamics. Beijing: Science Press, 168-201 (in Chinese)
Holl A, Althaus E, Lempp C. 1997． The petrophysical behavior of crustal rocks under the influence of fluids. Tectonophysics, 275: 253-260
Huenges E, Erizinger J, Kuck J. 1997． The permeable crust: Geohydraulic properties down to 9101 m depth. J. Geophys. Res. , 102 (B8) : 18255-18266
Jin Zhenmin, Green W H, Zhou Yi. 1994． Melt topology in partially molten peridotite during ductile deformation. Nature, 372: 164-167
Jin Shuyan, Jiao Shuqiang. 1998． Fabric measurements of omphacite from ultrahigh-pressure eclogite and rheological significances. Earth Science, 23(1) : 37-40 (in Chinese with English abstract)
Jin shuyan. 1997． Seismic anisotropy of continental lithosphere and its dynamical significances. In: Zhan Bingxi(ed. ). Modern methods for the lithospheric study. Beijing: Publishing House of Atomic Energy, 79-88 (in Chinese)
Jin Zhenmin, Yu Ridong, Yang Wencai and Ou Xingong. 2003． Mantle-derived xenoliths of peridotite from Pingmingshan, Uonghai County, Jiangsu province and their implications for deep structures. Acta Geologica Sinica, 77(4) :451-462 (in Chinese with English abstract)
Jones K A, Warner M R, Morgan R P. 1996． Coincident normal-incidence and wide-angle reflection from the Moho: evidence for crustal seismic anisotropy. Tectonophysics, 264(1-4) : 205-217
Jones T, Hur A. 1982． Seismic velocity and anisotropy in mylonites and reflectivity of deep crust fault zones. Geology, 10: 260-263
Kern H, Shao Gao, Zhenmin Jin, Popp T, Shuyan Jin. 1999． Petrophysical studies on rocks from the Dabie ultrahigh-pressure (UHP) metamorphic belt, Central China: implications for the composition and delamination of the lower crust. Tectonophysics, 301: 191-215
Kern H, Wenk H B. 1990． Fabric-related velocity anisotropy and shear-wave splitting in rocks from the Santo Rosa mylonite
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