新生代渤海中部强烈沉降的物理条件和深部过程
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摘要
新生代时期渤海中部的强烈沉降,是多种物理条件的共同作用结果,这些条件是由裂谷期和后裂谷期的深部过程产生成的.裂谷期在异常热地幔背景下的渤海地壳隆起、减薄、张裂,地幔热物质上升侵入地壳,莫霍界面位置升高,积累了重力势能;后裂谷期岩石圈(层)的冷却、收缩及下地壳的相变导致密度增大,加上巨厚沉积物的持续增生,使地壳处于重力不平衡状态,向下的垂直力远大于向上的浮托力,同时还有东部后退位移性板块边界和下地壳侧向流动的支持,使渤海中部成为下沉速率最快、沉降幅度最大的凹陷盆地.后裂谷期的早期的盆地下沉具有分散、局部性特征,表现为多个凹陷和凸起交替组合格局;晚期转变为大范围的整体沉降,显示重力均衡和补偿过程是从浅往深发展的.先存的郯庐断裂带对沉降的空间范围有局部边界控制性作用,其本身可能受到盆地发展的强烈改造影响.盆地的基本变形机制是上地壳的水平向脆性张破裂和垂直向或近垂直向的正断层-剪切破裂,地震震源机制解和大地震时的地表破裂表现的水平错动反映中、下地壳的走滑-平移型应力状态及相应的瞬间水平剪切破裂,它与上地壳残留的伸展、下沉相容并存于三维地壳体内.
Since Cenozoic time the middle Bohai Sea has been experienced intensive subsidence which results from the joint function of many physical conditions.These conditions were generated by deep processes during the rifting and post-rift periods.In the rift period the crust beneath the Bohai Sea uplifted,thinned,and ruptured extensionally,where the hot mantle materials intruded into the crust and the Moho interface rised,increasing gravity potential.In the post-rift period the cooling and contraction of the lithosphere as well as the phase change of the lower crust led to density growth.Added by increasing thickness of sediments,the crust of Bohai Sea was in the state of gravity non-balance,implying that the downward force was much greater than the upward buoyancy force.Meanwhile east to the Bohai Sea exists the plate boundary of retreat displacement,and the lower crust beneath this area can flow outward laterally.These factors results in subsidence of the middle Bohai Sea with the largest rate and amplitude.In the early stage the subsidence was scattered and local,exhibiting a mosaic pattern of alternating depressions and swells.The late stage of subsidence was featured by a large-scale and whole motion,indicating the isostatic compensation mechanism at depth became dominant.The pre-existing Tanlu fault zone bounded the development of the basin and was reformed strongly by the subsidence of the Bohai Sea.The essential mechanism of the basin evolution is the horizontal tensile rupture and normal faulting-nearly vertical shear fracture within the brittle upper crust.Meanwhile the focal solutions of modern earthquakes and co-seismic ruptures on the ground reflect the strike-slip faulting stress state in the middle and lower crust,which is compatible and co-existing with the extension and descending of the upper crust.
Since Cenozoic time the middle Bohai Sea has been experienced intensive subsidence which results from the joint function of many physical conditions.These conditions were generated by deep processes during the rifting and post-rift periods.In the rift period the crust beneath the Bohai Sea uplifted,thinned,and ruptured extensionally,where the hot mantle materials intruded into the crust and the Moho interface rised,increasing gravity potential.In the post-rift period the cooling and contraction of the lithosphere as well as the phase change of the lower crust led to density growth.Added by increasing thickness of sediments,the crust of Bohai Sea was in the state of gravity non-balance,implying that the downward force was much greater than the upward buoyancy force.Meanwhile east to the Bohai Sea exists the plate boundary of retreat displacement,and the lower crust beneath this area can flow outward laterally.These factors results in subsidence of the middle Bohai Sea with the largest rate and amplitude.In the early stage the subsidence was scattered and local,exhibiting a mosaic pattern of alternating depressions and swells.The late stage of subsidence was featured by a large-scale and whole motion,indicating the isostatic compensation mechanism at depth became dominant.The pre-existing Tanlu fault zone bounded the development of the basin and was reformed strongly by the subsidence of the Bohai Sea.The essential mechanism of the basin evolution is the horizontal tensile rupture and normal faulting-nearly vertical shear fracture within the brittle upper crust.Meanwhile the focal solutions of modern earthquakes and co-seismic ruptures on the ground reflect the strike-slip faulting stress state in the middle and lower crust,which is compatible and co-existing with the extension and descending of the upper crust.
引文
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[20]国家地震局地质研究所.郯庐断裂[C].北京:地震出版社,1987,109.
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[22]Ziegler P A.Geodynamics of rifting and implications for hy-drocarbon habitat[J].Tectonophysics,1992,215:221~253.
[23]Kay R W,Mahlburg-Kay S.Creation and destruction of low-er continental crust[J].Geol.Rundsch.,1991,80(2):259~278.
[24]Richardson S W,England P C.Metamorphic consequences ofcrustal eclogite production in orogenic overthrust zones[J].Earth Planet.Sci.Lett.,1979,42:183~190.
[25]严俊君,马前贵.渤海海域的郯庐扭断裂及含油气盆地的发育[J].地球科学-中国地质大学学报,1992,17(1):31-38.
[26]葛建党.郯庐断裂在渤中凹陷的构造特征与油气成藏的关系[J].海洋石油,2001,(1):14-20.
[27]龚在升.中国近海含油气盆地新构造运动与油气成藏[J].地球科学-中国地质大学学报,2004,29(5):513-517.
[28]Maerten L,Gillespie P,Pollard D D.Effects of local stressperturbation on secondary fault development[J].J Struct Ge-ol,2002,24:145~153.
[29]严俊君,王燮培.关于扭动构造的鉴别问题[J].石油与天然气地质,1996,17(1):8~14.
[30]Kusznir N J,Ziegler P A.Mechanics of continental extensionand sedimentary basin formation:a simple shear/pure-shearflexural cantilever model[J].Tectonophysics,1992,215:117~131.
[2]姜培海.渤海海域浅层油气勘探获得重大突破的思索[J].中国石油勘探,2001,6(2):77~86.
[3]漆家福,张一伟,陆克政,等.渤海湾新生代裂陷盆地的伸展模式及其动力学过程[J].石油实验地质,1995,17(4):316~323.
[4]滕吉文,张中杰,张秉铭,等.渤海地球物理场与深部潜在地幔热柱的异常构造背景[J].地球物理学报,1997,40(4):468~480.
[5]徐杰,马宗晋,邓起东,等.渤海中部渐新世以来强烈沉陷的区域构造条件[J].石油学报,2004,25(5):11~23.
[6]胡圣标,张容燕,罗毓晖,等.渤海盆地热历史及构造-热演化特征[J].地球物理学报,1999,42(6):748~755.
[7]Prawirodirdjo L,Bock Y.Instantaneous global plate motionmodel from 12 years of continuous GPS observations[J].JGeophys Res,2004,109,B08405,Doi:1029/2003JB002944.
[8]高祥林.琉球海沟的构造和运动特征[J].地球物理学进展,2003,18(2):293~301.
[9]Ma X,Wu D.Cenozoic extensional tectonics in North China[J].Tectonophysics,1987,133:243~255.
[10]Northrup C J,Royden L H,Burchfiel B C.Motion of the Pa-cific plate relative to Eurasia and its potential relation to Ce-nozoic extension along the eastern margin of Eurasia[J].Ge-ology,1995,23:719~722.
[11]陈国光,徐杰,马宗晋,等.渤海盆地现代构造应力场与强震活动[J].地震学报,2004,26:396~403.
[12]高祥林.华北地区构造应力状态沿垂直方向的变化及其成因[M].见:国家地震局地质研究所,现代地壳运动研究(4),64~68.北京:地震出版社.
[13]李嘉琪.决定渤海重磁力异常的主要地质因素[J].海洋地质与第四纪地质,1984,4(4):21~34.
[14]刘光夏,赵文俊,李志雄,等.渤海第三纪裂谷扩张的地球物理分析[J].西北地震地震学报,18(3):18~24.
[15]刘福田,曲克信,吴华,等.中国大陆及其邻近地区的地震层析成像[J].地球物理学报,1989,32:281~291.
[16]宋晓东,李思田,李迎春,等.岩石圈地幔结构及其对中国大型盆地的演化的意义[J].地球科学-中国地质大学学报,2004,29:531~538.
[17]孙若昧,赵燕来,梅世蓉.渤海及其邻区的地震层析成像[J].地球物理学报,1993,36:44~54.
[18]Lerch F J,Klosko S M,Patel G B,et al.A gravity modelfor crustal dynamics(GEM-L2)[J].J Geophys Res,1985,90:9301~9311.
[19]侯廷贵,钱祥麟,蔡东升.渤海-鲁西地区白垩-早第三纪裂谷活动-火山岩的地球化学证据[J].地质科学,2003,38(1):13~21.
[20]国家地震局地质研究所.郯庐断裂[C].北京:地震出版社,1987,109.
[21]Bally A W,Bender P L,McGetchin T R,et al.Dynamics ofPlate Interiors[J].Washington D C:American GeophysicalUnion,1980.
[22]Ziegler P A.Geodynamics of rifting and implications for hy-drocarbon habitat[J].Tectonophysics,1992,215:221~253.
[23]Kay R W,Mahlburg-Kay S.Creation and destruction of low-er continental crust[J].Geol.Rundsch.,1991,80(2):259~278.
[24]Richardson S W,England P C.Metamorphic consequences ofcrustal eclogite production in orogenic overthrust zones[J].Earth Planet.Sci.Lett.,1979,42:183~190.
[25]严俊君,马前贵.渤海海域的郯庐扭断裂及含油气盆地的发育[J].地球科学-中国地质大学学报,1992,17(1):31-38.
[26]葛建党.郯庐断裂在渤中凹陷的构造特征与油气成藏的关系[J].海洋石油,2001,(1):14-20.
[27]龚在升.中国近海含油气盆地新构造运动与油气成藏[J].地球科学-中国地质大学学报,2004,29(5):513-517.
[28]Maerten L,Gillespie P,Pollard D D.Effects of local stressperturbation on secondary fault development[J].J Struct Ge-ol,2002,24:145~153.
[29]严俊君,王燮培.关于扭动构造的鉴别问题[J].石油与天然气地质,1996,17(1):8~14.
[30]Kusznir N J,Ziegler P A.Mechanics of continental extensionand sedimentary basin formation:a simple shear/pure-shearflexural cantilever model[J].Tectonophysics,1992,215:117~131.
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