蒙古-贝加尔裂谷区地壳应变场及其地球动力学涵义
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摘要
蒙古-贝加尔地区是现今构造最活跃的大陆地区之一,其地壳构造运动及变形对我们理解大陆动力学问题具有重要的科学意义.基于融合的这一区域的GPS速度场,本文计算了该区应变率场和应变能变化率场.结果显示,蒙古褶皱带以南区域表现为NNE-SSW方向的压缩状态,主压应变率约为-2.0×10~(-9)/a,剪应变及面膨胀均较弱,表明蒙古褶皱带比较稳定.贝加尔裂谷整体处于拉张状态且伴有较强的剪应变和面膨胀,暗示可能有多种机制控制裂谷的张裂过程.蒙古高原西部有两条高应变率的构造带,结合深部存在地幔热柱等证据,我们认为这两条构造带及所围限的区域共同构成Amurian板块的西部边界—一条弥散变形的边界带.蒙古-贝加尔地区剪应变分布与0～40 km的地震活动性基本一致,表明该地区形变在地壳尺度耦合程度较高.地幔对流拖曳力场与主应变轴方向及应变率场的一致性表明,地幔对流可能是蒙古贝加尔地区区域构造动力学过程主要控制因素之一.
The tectonics and crustal deformation of the Mongolia-Baikal Rift Zone(MBRZ),which is one of the most active tectonic zones in continents,is significant for understanding continental dynamics.Based on combined GPS velocities of MBRZ,the strain rate field and the strain energy variation were calculated.It is found that the Mongolian fold belt is characterized by a NNE-SSW compression with a small rate of 2.0×10~(_9)/a,indicating the Mongolian fold belt is stable in current tectonics.The Baikal Rift Zone(BRZ)is being extended with a maximum strain rate of 2.5×10~(-8)/a and high shear strain and dilation are found along BRZ,which implies that the rifting of BRZ may be controlled by various mechanisms.Two high-strain belts are found in western Mongolia,combining the evidence of mantle plumes in deep region,we suggest that the two belts and the enclosed region could be regarded as the west boundary of the Amurian plate-a diffused deformation boundary zone.The consistency between the shear strain pattern and the seismicity with hypocenter depth less than 40 km indicates a high level of coupling of deformation within crust.The consistency between the mantle convection-generated drag force and the principle axis of strain and strain rate suggests that mantle convection might be one of the controlling factors for regional tectonic process in MBRZ.
The tectonics and crustal deformation of the Mongolia-Baikal Rift Zone(MBRZ),which is one of the most active tectonic zones in continents,is significant for understanding continental dynamics.Based on combined GPS velocities of MBRZ,the strain rate field and the strain energy variation were calculated.It is found that the Mongolian fold belt is characterized by a NNE-SSW compression with a small rate of 2.0×10~(_9)/a,indicating the Mongolian fold belt is stable in current tectonics.The Baikal Rift Zone(BRZ)is being extended with a maximum strain rate of 2.5×10~(-8)/a and high shear strain and dilation are found along BRZ,which implies that the rifting of BRZ may be controlled by various mechanisms.Two high-strain belts are found in western Mongolia,combining the evidence of mantle plumes in deep region,we suggest that the two belts and the enclosed region could be regarded as the west boundary of the Amurian plate-a diffused deformation boundary zone.The consistency between the shear strain pattern and the seismicity with hypocenter depth less than 40 km indicates a high level of coupling of deformation within crust.The consistency between the mantle convection-generated drag force and the principle axis of strain and strain rate suggests that mantle convection might be one of the controlling factors for regional tectonic process in MBRZ.
引文
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[5] Bayasgalan A,Jackson J,Ritz J F,et al.Field examples of strike-slip fault terminations in Mongolia and their tectonic significance[J].Tectonics,1999,18:394～411．
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[13] 李延兴,张静华,何建坤,等.菲律宾海板块的整体旋转线性应变模型与板内形变-应变场[J].地球物理学报,2006,49(5) :1339～1346． Li Y X,Zhang J H,He J K,et al.Integral-rotation linear strain model and intraplate deformation-strain field of the Philippine Sea Plate[J].Chinese J.Geophys.(in Chinese),2006,49(5) :1339～1346．
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[15] 许才军,董立祥,施闯,李延兴,胡新康.华北地区GPS地壳应变能密度变化率场及其构造运动分析[J].地球物理学 报.2002,45(5) :497～506． Xu C J,Dong L X,Shi C,Li Y X,Hu X K.A study on annual accumulation of strain energy density significance by using GPS measure~nents in north China[J].Chinese J.Geophys.(in Chinese),2002,45(5) :497～506．
[16] IinumaT,Kato T,Hori M.Inversion of GPS velocity and seismicity data to yield changes in stress in the Japanese Islands[J].Geophys.J.Int,2005,180:417～434．
[17] Jin S G,Park P H.Crustal stress and strain energy density rates in south Korea deduced from GPS observations[J].TAO,2006,17(1) :169～178．
[18] Logatchev N,Florensov N.The Baikal rift:active or passive?Comparison of the Baikal and Kenya rift zones[J].Tectophysics,1978,4:223～ 240．
[19] San'kov V A,Chipizubov A V,Lukhnev A V,et al.Assessment of a large earthquake risk in the zone of main Sayan fault using GPS Geodesy and Paleoseismology[J].Russia Geology Geophys,2004,45(11) :1369～1376．
[20] Koulakov I.Three dimensional seismic structure of the upper mantle beneath the central part of the Eurasian continent[J].Geophys.J.Int,1998,133:467～489．
[21] 王继业.蒙古高原及邻区上地幔小尺度对流研究.硕士学位 论文[D].武汉:中国科学院测量与地球物理研究所,2006． Wang J Y,Study on small-scale convection within upper mantle beneath the Mongolia Plateau and its adjacent areas[D].(in Chinese).Wuhan:Institute of Geodesy and Geophysics,Chinese Academy of Science.2006．
[22] 熊熊,滕吉文,郑勇.中国大陆地壳运动的GPS观测及相关动力学研究[J].地球物理学进展,2004,19(1) :16～25． Xiong X,Teng J W,Zheng Y.GPS observations for crustal movements in China continent and related geodynamic studies[J].Progress in Geophysic(in Chinese),2004,19(1) :16～ 25．
[23] Gao S,Davis P M,Liu H,et al.Asymmetric upwarp of the asthenosphere beneath the Baikal rift zone,Siberia[J].J.Geophys Res.,1994,99:15319～15330．
[24] Molnar P,Tapponnier P.Cenozoic tectonic of Asia:effects of a continental collision]J].Science,1975,189:419～426．
[25] Savostin L A,Verzhbitskaya A I,Baranov B V.Holocene plate tectonics of the Sea of Okhotsk region[J].Dokl.Acad.Sci.USSR,Earth Planet Sci Let,1982,18:269～311．
[26] Heki K,Miyazaki S,Takahashi H,et al.The Amurian Plate motion and current plate kinematics in eastern Asia[J].J.Geophys Res.,1999,104(B2) :29147～29155．
[2] Calais E,Vergnolle M,Vladimir San'kov,et al.GPS measurements of crustal deformation in the Baikal-Mongolia area(1994-2002) :Implications for Current kinematics of Asia[J].J.Geophys.Res.,2003,108:1～13．
[3] Calais E,Lesen O,D è verch è re J,et al.Crustal deformation in the Baikal rift from GPS measurements[J].Geophys.Res.Lett,1998,25:4003～4006．
[4] Cunningham W D,Cenozoic normal faulting and regional doming in the southern Hangay region,Gentral Mongolia:implications for the origin of the Baikal rift province[J].Tectonophysics,2001,331:389～411．
[5] Bayasgalan A,Jackson J,Ritz J F,et al.Field examples of strike-slip fault terminations in Mongolia and their tectonic significance[J].Tectonics,1999,18:394～411．
[6] Calais E,Vergnolle M,Deverch è re J,et al.Are post-seismic effects of the M=8． 4 Bolnay earthquake(1905,July 23) still influencing GPS velocities in the Mongolia-Baikal area?[J].Geophys.J.Int.,2002,148:1～12．
[7] Calais E,Dong L,Wang M,et al.Continental deformation in Asia from a combined GPS solution[J].Geophys.Res.Let.,2006,33:L24319～L24322．
[8] 赖锡安,黄立人,徐菊生,等编著.中国大陆现今地壳运动[M].北京:地震出版社,2004． Lai X A,Huang L R,Xu J S,et al.The present-day crustal movement in China continent[M].(in Chinese)Beijing:Seismological Press,2004．
[9] 杨国华,李延兴,韩月萍,胡新康,巩曰沐.由GPS观测结果推导中国大陆现今水平应变场[J].地震学报.2002,24(4) :337～347． Yang G H,Li Y X,Han Y P,HU X K,Gong M Y,Current horizontal strain field in Chinese mainland derived from GPS data[J].Acta Seismologica Sinica,(in Chinese).2002,24(4) :337～347．
[10] Holt W E,Chamot R N,Le Pichon X,et al.Velocity field in Asia inferred from Quaternary fault slip rates and Global Positioning System observations[J].J.Geophys.Res.,2000,105(B8) :19185～19209．
[11] 朱守彪,蔡永恩,石耀霖,青藏高原及邻区现今地应变率场的计算及其结果的地球动力学意义[J].地球物理学报,2005,48(5) :1053～1061． Zhu S B,Cai Y E,Shi Y L.Computation of the present day strain rate field of the Qinghai-Tibetan plateau and its geodynamic implications[J].Chinese J.Geophys.(in Chinese),2005,48(5) :1053～1061．
[12] 李延兴,李智,张静华,黄珹,朱文耀,王敏,郭良迁,张中伏,杨春花.中国大陆及周边地区的水平应变场[J].地球物理学报,2004,47(2) :222～231． Li Y X,Li Z,Zhang J H,Huang C,Zhu W Y,Wang M,Guo L Q,Zhang Z F,Yang C H.Horizontal strain field in the Chinese mainland and its surrounding areas[J].Chinese J.Geophys.(in Chinese),2004,47(2) :222～231．
[13] 李延兴,张静华,何建坤,等.菲律宾海板块的整体旋转线性应变模型与板内形变-应变场[J].地球物理学报,2006,49(5) :1339～1346． Li Y X,Zhang J H,He J K,et al.Integral-rotation linear strain model and intraplate deformation-strain field of the Philippine Sea Plate[J].Chinese J.Geophys.(in Chinese),2006,49(5) :1339～1346．
[14] 李延兴,张静华,何建坤,等.由空间大地测量得到的太平洋板块现今构造运动与板内形变应变场[J].地球物理学报,2007,50(2) :437～447． Li Y X,Zhang J H,He J K,et al.Current-day tectonic motion and intraplate deformation-strain field obtained from space geodesy in the Pacific Plate[J].Chinese J.Geophys.(in Chinese),2007,50(2) :437～447．
[15] 许才军,董立祥,施闯,李延兴,胡新康.华北地区GPS地壳应变能密度变化率场及其构造运动分析[J].地球物理学 报.2002,45(5) :497～506． Xu C J,Dong L X,Shi C,Li Y X,Hu X K.A study on annual accumulation of strain energy density significance by using GPS measure~nents in north China[J].Chinese J.Geophys.(in Chinese),2002,45(5) :497～506．
[16] IinumaT,Kato T,Hori M.Inversion of GPS velocity and seismicity data to yield changes in stress in the Japanese Islands[J].Geophys.J.Int,2005,180:417～434．
[17] Jin S G,Park P H.Crustal stress and strain energy density rates in south Korea deduced from GPS observations[J].TAO,2006,17(1) :169～178．
[18] Logatchev N,Florensov N.The Baikal rift:active or passive?Comparison of the Baikal and Kenya rift zones[J].Tectophysics,1978,4:223～ 240．
[19] San'kov V A,Chipizubov A V,Lukhnev A V,et al.Assessment of a large earthquake risk in the zone of main Sayan fault using GPS Geodesy and Paleoseismology[J].Russia Geology Geophys,2004,45(11) :1369～1376．
[20] Koulakov I.Three dimensional seismic structure of the upper mantle beneath the central part of the Eurasian continent[J].Geophys.J.Int,1998,133:467～489．
[21] 王继业.蒙古高原及邻区上地幔小尺度对流研究.硕士学位 论文[D].武汉:中国科学院测量与地球物理研究所,2006． Wang J Y,Study on small-scale convection within upper mantle beneath the Mongolia Plateau and its adjacent areas[D].(in Chinese).Wuhan:Institute of Geodesy and Geophysics,Chinese Academy of Science.2006．
[22] 熊熊,滕吉文,郑勇.中国大陆地壳运动的GPS观测及相关动力学研究[J].地球物理学进展,2004,19(1) :16～25． Xiong X,Teng J W,Zheng Y.GPS observations for crustal movements in China continent and related geodynamic studies[J].Progress in Geophysic(in Chinese),2004,19(1) :16～ 25．
[23] Gao S,Davis P M,Liu H,et al.Asymmetric upwarp of the asthenosphere beneath the Baikal rift zone,Siberia[J].J.Geophys Res.,1994,99:15319～15330．
[24] Molnar P,Tapponnier P.Cenozoic tectonic of Asia:effects of a continental collision]J].Science,1975,189:419～426．
[25] Savostin L A,Verzhbitskaya A I,Baranov B V.Holocene plate tectonics of the Sea of Okhotsk region[J].Dokl.Acad.Sci.USSR,Earth Planet Sci Let,1982,18:269～311．
[26] Heki K,Miyazaki S,Takahashi H,et al.The Amurian Plate motion and current plate kinematics in eastern Asia[J].J.Geophys Res.,1999,104(B2) :29147～29155．
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