利用被动源地震剖面研究龙门山断裂带邻区的深部结构
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摘要
自2005年以来,我们跨龙门山断裂带布设了龙泉驿至道孚(剖面1)和资阳至玛曲(剖面2)两条被动源地震剖面。利用被动源剖面记录到的远震地震波数据通过接收函数方法对其进行接收函数反演成像,得到每个台站下方地壳上地幔的速度界面。并结合研究区台站下的S波速度和人工地震剖面的地壳分层速度分布,对地壳结构、活断层面滑脱面进行研究,对于探讨青藏高原东缘龙门山与扬子克拉通的碰撞接触关系动力学问题具有重要的意义。
     研究结果表明:
     1.扬子地台西缘地壳厚度在35~48km的横向变化;在龙门山推覆体莫霍面起伏变化不大,地壳厚度约45km;松潘甘孜地块在剖面1中莫霍面由跨过龙门山中央断裂带后形成一个16~20km的陡降带,地壳厚度在45~68km之间变化;而在剖面2中莫霍面在跨过龙门山后山断裂带西侧约30km形成12km左右的缓降带,地壳厚度在45~58km之间变化。这结果表明从扬子板块向西至松潘甘孜地块,地壳厚度逐渐增厚,松潘甘孜地块南面莫霍面比北面深约10km左右,剖面1在龙门山推覆体内形成的陡降带与龙门山汶川主震位置的中央断裂带走势一致,而剖面2在龙门山推覆体内形成的陡降带距离龙门山中央断裂带约70km左右,这与龙门山中央断裂带的走势不一致,也与地貌和地表构造特征不吻合。根据扬子板块和松潘甘孜地块地壳厚度的分区性,说明:松潘甘孜地块南部—龙门山地带是莫霍界面强烈变化转折部位,是扬子地块西缘和松潘甘孜地块的构造边界;松潘甘孜北部—莫霍面强烈变化部位在龙门山中央断裂西侧70km,是扬子地块西缘和松潘甘孜地块的构造边界,龙门山构造带不是扬子地块西缘和松潘甘孜地块的构造边界。
     2.松潘-甘孜地块及龙门山推覆体的中地壳内20~30km存在一个厚10km左右的朝北西缓倾并转为近水平延伸的低速层,该低速层的南东端结束于龙门山中央断裂与前山断裂之间的下方。龙门山前山断裂以东的扬子地台西缘地壳壳内低速层不发育。松潘-甘孜地块及龙门山推覆体中的低速中地壳易形成滑脱层,使其上覆的上地壳与低速中地壳滑脱拆离,脆性上地壳向东仰冲推覆,使得比较软的松潘-甘孜地块对坚硬的四川陆块,在龙门山由北西向南东逆冲推覆滑动形成了走滑-逆冲推覆构造,并形成前山、中央和后山几条主要铲式断层。龙门山推覆体上覆上地壳和中下地壳滑脱拆离,致使剖面2得到的莫霍面在白溪乡东侧缓降带与地表断裂带不一致。
     3.松潘甘孜地块岩石圈厚度在130~180km之间,软流圈下界面深约280~290km;龙门山推覆体岩石圈厚度约为140km,软流圈下界面深约260~280km;扬子地块岩石圈厚度为130~140km,软流圈下界面深约270~290km。从扬子地块至松潘甘孜地块向西岩石圈厚度逐渐增厚,起伏不大;软流圈下界面深度无大的起伏,也无明显变化规律。扬子地块和松潘甘孜地块同时存在410km和660km间断面。
We have deployed two passive seismological profiles across Longmenshan fault zone since 2005,namely, profile 1 extending from Longquanyi to Daofu and profile 2 extending from Ziyang to Maqu. The seismic data from distant earthquakes, acquired from both profiles, have been analyzed to obtain velocity interfaces within lithosphere and upper mantle for each station via teleseismic receive function method. Combining the S-waves velocity data, crustal layering and velocity distribution in the seismic profiles, the crustal structure, active fault asperity and detachment surface. This thesis is to illustrate several significant implications for the kinematical mechanism of collision between Eastern Tibetan plateau and Yangtze craton.
     Our research has made three main discoveries, as follows,
     1. The crust thickness of Western margin of the Yangtze craton ranges from 35 to 48 km. The Moho boundary under Longmenshan nappe is of little ups and downs around 45 km. The Moho boundary forms a rapidly decreasing zone of 16~20 km, starting from the East across Longmenshan central fault zone towards Songpan-Ganzi block, with the crustal thickness decreasing from 45 to68 km. In profile 2, a 12 km decrease of Moho depth from 30 kmacross the Longmenshan fault zone, is a gentles decrease compared to the previous one. The crustal thickness ranges from 45~58 km. These results both demonstrate the thickness of the crust increases from Yangtze craton to Songpan-Ganzi block.The crustal thickness of southern Songpan-Ganzi block is 10 km thicker than its northern counterpart. In profile 1, the direction of the decrease zone located in the Longmenshan nappe is consistent with the direction of the Longmengshan central fracture zone.However, in profile 2, the decrease zone within the Longmenshan nappe is 70 km apart from the Longmenshan central fracture zone, showing inconsistence with both Longmenshan central fault zone and topographic features. Based on the crustal thickness partition property of Yangtze and Songpan-Ganzi block, we propose that Songpan-Ganzi block south-Longmenshan is the tipping point of the Moho depth and also the tectonic boundary between western Yangtze craton and Songpan-Ganzi block ; Songpan-Ganzi block north- the decrease zone within the Longmenshan nappe is 70 km apart from the Longmenshan central fracture zone and also the tectonic boundary between western Yangtze craton and Songpan-Ganzi block.
     2. A low-velocity zone with the thickness around 10 km is located in the middle crust (20~30 km depth) of Songpan-Ganzi block and Longmenshan nappe region. This low-velocity zone slightly dips northwestward then and turns to be lateral with its southeast end between the Longmenshan central fault zone and the front hill fault zone. There is no sign showing this same low-velocity zone existing in the crust of Yangtze craton and Songpan-Ganzi block. The existence of this low-velocity middle crust makes it easy to form detachments between the upper crust and the middle crust in these regions.Furthermore, the force from the Tibetan plateau push the detached upper crust to the East, resulting in the northwestern dipping thrust nappe structure as well as three main fault zones in the Longmenshan region. The same detachment in the between the upper crust and middle-lower crust in Longmenshan causes the inconsistence observed along profile 2.
     3. The thickness of the lithosphere of Songpan-Ganzi block is between 130~180 km, with the depth of the bottom of asthenosphere at about 280~290 km. The thickness of the lithosphere in Longmenshan nappe belt region is around 140 km with the depth of the bottom of asthenosphere at about 260~280 km. For the Yangtze craton, the lithosphere thickness is 130~140 km and the depth of asthenosphere locates at 270~290 km. From these data, we can conclude that the lithosphere thickness from Yangtze craton to Songpan-Ganzi block has a slight but steady increase and the depth of the asthenosphere barely changes across these two tectonic bodies. There exist 410-km-discontinuity and 660-km-discontinuity under both the Yangtze craton and the Songpan-Ganzi block.
引文
[1]藤吉文,杨辉,张洪双等.汶川映秀8.0级大地震的发生与岩石圈精细速度结构和动力机制[J].中国科学D辑:地球科学,2010,30(4):637~651.
    [2]李海丰.青藏高原东缘龙门山被动源地震剖面台阵研究[D].成都理工大学硕士学位论文,2008.
    [3]陈九辉.远震体波接收函数方法:理论与应用[D].中国地震局地质研究所博士学位论文,2007.
    [4]孙丽,刘瑞丰,黄志斌等.用接收函数研究川滇地区国家地震台下地壳厚度波速比[J].中国地震,2008,24(4):362~369.
    [5]宋文杰,朱介寿,程先琼等.汶川Ms8.0级地震震源区地壳深部结构研究[J],第四纪研究,2010,30(4),670~676.
    [6]蔡学林、曹家敏、刘援朝等.青藏高原多向碰撞楔入隆升地球动力学模式[J].地学前缘,1999,6(3),181~188.
    [7]柳畅.接收函数反演KMI地震台站下方地壳结构研究[D].中国地质大学(北京)硕士学位论文, 2005.
    [8]李海鸥.富蕴-库尔勒宽频地震探测深部构造[D].中国地质大学(北京)博士学位论文,2006.
    [9]刘瑞丰,杨辉,邹立晔等.国家数字地震台网分中心地震波形数据管理和服务系统[J].国际地震动态,2004,309(9),33~37.
    [10]黄金莉,顾小虹.国家数字地震台网中心应用地震波形数据格式转换[J].地震,2001, 21(4):60~65.
    [11]何加勇,李松林,陈会中.地震波形归档格式分析和转换[J].震灾防御技术,2009,4(4):461~465.
    [12]刘启元,Rainer Kind.分离三分量远震接收函数的多道最大或然性反褶积方法[J].地震地质,2004,26(3):416~425.
    [13]Owens TJ ,Taylor S R ,Zandt G. Isolation and enhancement of the response of local seismic structure from teleseismic P waveforms [M].1983,UCID - 19809 33 PP.Livermore Natl Lab ,Livermore ,Calif .
    [14]贺传松,王椿镛,吴庆举.接收函数方法其新的进展[J].地球物理学进展,2003,18(2):224~228.
    [15]许卫卫,郑天愉,接收函数方法研究进展[J].地球物理学进展,2002,17(4):605~613.
    [16]邹最红,陈晓非.利用SV分量接收函数反演地壳横波速度结构[J].地震学报,2003,25(1):15~23.
    [17]楼海,王椿镛,吕智勇等.2008年汶川Ms8.0级地震的深部构造环境-远震P波接收函数和布格重力异常的联合解释[J].中国科学D辑:地球科学,2008,38(10):1207~1220.
    [18]刘启元,李昱,陈九辉等.汶川Ms8.0地震:地壳上地幔S波速度结构的初步研究[J].地球物理学报,2009,52(2):309~319.
    [19]嘉世旭,张先康,赵金仁等.若尔盖盆地周缘褶皱造山带地壳结构-深地震测深结果[J].中国科学D辑:地球科学,2009,39(9):1200~1208.
    [20]嘉世旭,张先康.青藏高原东北缘深地震测深震相研究与地壳细结构[J].地球物理学报,2008,51(5):1431~1443.
    [21]雷建设,赵大鹏,苏金蓉等.龙门山断裂带地壳精细结构与汶川地震发震机理[J].地球物理学报,2009,52(2):339~345.
    [22]朱介寿.汶川地震的岩石圈深部结构与动力学背景[J].成都理工大学学报(自然科学版),2008,35(4):348~356.
    [23]刘启元,陈九辉,李顺成等.汶川Ms8.0地震:川西流动地震台阵观测数据的初步分析[J].地震地质,2008,30(3):584~596.
    [24]杜方,闻学泽,张培震等.2008年汶川8.0级地震前横跨龙门山断裂带的震间形变[J].地球物理学报,2009,52(11):2729~2738.
    [25]蔡学林,王绪本,朱介寿等.汶川8.0级特大地震震源断裂特征其动力学分析[J].中国地质,2010,37(4):952~966.
    [26]刘树根,田小彬,李智武等.龙门山中段构造特征与汶川地震[J].成都理工大学学报(自然科学版),2008,35(4):388~397.
    [27]Cai Xuelin,Wei Xiangui,Liu Yuanchao,et al.On the wedging-in orogensisis[C].//Progress in Geology of the China(1993-1996)-Papers to 30th IGC.Beijing:China Ocean Press,1996:314~320.
    [28]国家重大科学工程《中国地壳运动观测网络》项目组.GPS测定的2008年汶川Ms8.0地震的同震位移[J].中国科学(D辑),2008,38(10):1195~1206.
    [29] Tapponnier P.Peltzer G,Le Dain A Y,et al.Propagating extrusion tectonics in Asia: New insights from simple experiments with plasticine.Geology[J]. 1982,10(12):611~616.
    [30]Zhang P Z.Shen Z K,Wang M,et al. Continuous deformation of the Tibetan Plateau from Global Positioning System data[J]. Geology.2004,32(9):809~812.
    [31]李永华,吴庆举,安张辉等.青藏高原东北缘地壳S波速度结构与泊松比其意义[J].地球物理学报,2006,49(5):1359~1368.
    [32]张世民,谢富仁,黄忠贤等.龙门山地区上地壳的拱曲冲断作用其深部动力学机制探讨[J].第四纪研究,2009,29(3):449~463.
    [33]Xiaohui Yuan,James Ni,Rainer Kind,et al.Lithospheric and upper mantle structure of southern Tibet from a seismological passive source experiment.Journal of Geophysical[J].1997 ,102(27):491~500.
    [34]段永红.中国东北西太平洋俯冲带火山区地壳上地幔结构研究[D].中国地震局地球物理研究所博士学位论文,2005.
    [35]徐锡伟,闻学泽,叶建青等.汶川MS8.0地震地表破裂带其发震构造[J].地震地质,2008,30(3): 597~629.
    [36]李海兵,司家亮,付小方等.2008年汶川地震同震滑移特征、最大滑移量构造意义[J].第四纪研究,2009,29(3):387~402.
    [37]朱介寿,李海丰,Alexandra Robert,等.青藏高原东缘龙门山岩石圈深部结构[J].中国地质地球物理研究进展,海洋出版社,2008.66~74.

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