【作者】 王有学；

【导师】 余钦范； 姜枚；

【作者基本信息】 中国地质大学（北京） ， 地球探测与信息技术， 2003， 博士

【摘要】 苏鲁—大别位于我国东部，是继西阿尔卑斯和挪威发现含柯石英包体的镁铝榴石石英岩和榴辉岩之后发现的又一超高压变质造山带，成为全球最大的超高压变质带。自80年代中期以来，该造山带已受到国际地学界的关注，成为超高压变质作用和大陆动力学的重要区域之一。本文通过对苏鲁—大别超高压变质造山带的广角地震测深研究，结合该地区其它地质及地球物理资料取得了一些新成果，主要归纳如下： 1．提出二维介质中的空间变量分离速度成像技术，该方法适用于折射及反射波。在成像过程中，反射层内部的速度描述不再局限于常速或线性分布，可以更为复杂。对该方法进行了模型试算，取得了良好的成像效果，同时还对各反演参数对成像效果的影响进行了分析。模型试算结果表明，该方法具有很大的灵活性。首先它对初始模型的依赖性较小，通过几次迭代即可重现介质的结构特征；其次在各层的重建过程中可以根据具体的地质构造背景及可能的介质的复杂程度，选取适当的m、n值，使之计算更为有效；同时将反射波数据纳入成像过程，亦获得较为满意的结果。 由于受所使用的数据信息量的限制，本文仅利用该方法对苏鲁大别地区的深部地震测深资料的浅部资料进行了处理解释，得到较满意的应用效果。 2．提出广角反射波“动校正”方法，并将其应用于莫霍面的反射波资料的处理解释，使解释结果更为直观。 3．利用纵、横波资料的联合解释，建立了苏鲁—大别地区地壳的泊松比结构，从而使得我们可能对地壳的物质组成进行了推断。一般来说，花岗质酸性岩类具有较小的泊松比值，玄武质等基性及超基性岩类具有更大的泊松比值，而诸如片麻岩等中性岩类则介于二者之间。实验测定和理论研究表明，地壳中Vp和Vs同岩石中二氧化硅的含量有着密切的关系，因而可根据地壳中Vp和Vs的分布特征确定固结地壳中的二氧化硅含量，进而可利用纵、横波的波速比或泊松比对地壳内部的物质组成进行深入的研究。 4．通过对苏鲁超高压变质带中的中国大陆科学钻探钻址场区的地壳结构研究，其结果表明：东海地区的地壳结构可以R₄、R₅及Rm等界面将其划分为上、中、下三层：R₄以上为上地壳，速度小于6.20km／s，其中上部（R₁界面以上部分）由地表混杂岩组成，下部由超高压变质岩体层（R₂与R₃之间）与基底层（R₃与R₄之间）夹低速层构成，该低速层的泊松比仅为0.23-0.235，可能对应于一个剪切带或变质的花岗岩侵入体，推测为花岗片麻岩或酸性麻粒岩花岗岩；中地壳由位于R₄与R₅界面之间的地层构成，其速度为6.40km／s，推测其为中性麻粒岩及闪长岩；下地壳由速度为6.60km／s的介质层构成，泊松比为0。265，可能由基性麻粒岩组成。 超高压变质层表现为西深东浅，南北向呈现为一微隆形态，大陆科学钻探钻址下部的埋深为2.4km，其厚度约为2.1km。低速层在大陆科学钻探钻址下部的埋深为2.0km左右。在中部地区的中上地壳存在一个隆起，与超高压变质带相对应。苏鲁地区的地壳厚度为31km，平均速度为6.30km／s左右。 5．同苏鲁地区的地壳结果相比较，通过地质、地球物理资料的综合研究，大别山高压超高压造山带的地壳同样也可以划分为上、中、下三层结构，但在上地壳中却没有发现低速层的存在。在霍山附近，地表浅部南侧的地表杂岩带同北侧的中新生代沉积在速度分布上形成明显的对比，且向北速度急剧变小；浅部的反射界面也存在较大的落差；中、上地壳在大别山造山带呈现为隆起带形态，且呈高速特征；Moho面在南部由南至北逐渐加深，宿松一带仅为32km，而在霍山下部却由南侧的43kin向北突然抬升至35km。中地壳的速度在6．20－6．35kin／S范围内变化，具有造山带中地壳速度6．38士0．34km／s特征，但似乎仍有些偏低，这可能是由于在大别山造山带的形成过程中，酸性或中酸性花岗岩侵人中地壳造成的；下地壳亦没有典型的地台下地壳的高速(7．0－7．4k血功特征，仅为6．50－6．70k二八：在属于扬子陆块的南部地区，上地慢顶部的速度分布亦同北侧的华北陆块存在着明显的差异，扬于陆块为7．75km八，而华北陆块则为7．90km乃。无论从地表浅部还是从地壳深部及莫霍面的形态，都强烈地支持晓天一磨子潭断裂为华北陆块与扬子陆块的碰撞缝合带，并且显示出扬子板块向北俯冲的趋势。 在大别造山带中存在一个形态为倒三角形的高速、高泊松比（0．26－0．28）异常块体，可能由基性麻粒岩及变质辉长角闪岩组成，主要分布干中、下地壳，在地表为大别高压超高压变质带及北大别杂岩带所覆盖，且南、北两侧分别为太湖一马庙及晓天一磨子潭断裂所夹持，推测其为大别激古陆块的所在。所谓的南、北大别分界水吼一五河断裂仅为一地表断裂，切穿深度并不大；地表所看到的南、北大别的差异仅仅是由于后期改造所造成的。这在其他地球物理资料也有明显的反映，进而推断大别高压超高压变质造山带的南北之分很可能并不存在。 6．苏鲁一大别超高压造山带的地质地球物理资料的综合研究和分析结果表明，苏鲁——大别超高压变质造山带的形成演化过程同部庐断裂的形成与演化过程有着密切的关系。在古更多还原

【Abstract】 After the discoveries of coesite-bearing eclogites in Western Alps and Norway, Sulu-Dabie becomes the largest Utralhigh-Pressure (UHP) metamorphic belt in the world. Since the middle of 1980s, many geoscientists have paid their attentions to this erogenic belt, and considered it as a natural laboratory for studying the Utralhigh-Pressure mechanism and continental geodynamics. Combining with the previous geological and geophysical data, this paper will try to describe the characteristics of the crustal structure beneath the huge UHP belt. The main results are given below:1. An imaging method, Partitioning-Variables Velocity Imaging Method in 2D Media, was put forward, and this method is applicable not only for refraction and reflection seismic data but also for complicated velocity distributions within a layer. Through model testing and analyzing, the method rarely depends on the initial velocity model, and the image will be reconstructed after just a few iterations. It will be more effective when the parameters, m and n, take appropriate values according to the geological background in the imaging area.Because of no enough information in the acquired data sets, only the shallow structures are reconstructed in this study with fine results in this dissertation.2. The ’Moveout’ technique for wide-angle reflection is put forward and applied to the deep seismic sounding, especially to the reflection from the Moho, and it makes the interpretation more intuitionistic.3. The Poisson’s ratio structures in Sulu and Dabie erogenic belts are obtained by using the P- and S-wave data, and make it possible to infer the composition within the crust. Generally, a lower Poisson’s ratio corresponds to the rocks like felsic granite, while higher Poisson’s ratio corresponds to the mafic or utralmafic rocks like basalt, and the value between the two above corresponds to the rocks like gneiss. The results from these experiments and theoretical research reveal that the silicon content in the rock is related to the velocities of P- and S-wave when they propagate through the rock, thus the composition of the crust can be infered according to the Poisson’s ratio which obtained by the P- and S-wave velocities.4. The research on the Chinese Continental Deep Drilling site in the Sulu Utralhigh-Pressure Metamorphic Belt indicates that the crust can be divided into three layers. The upper crust is composed of the layers above the boundary RI, middle crust between boundaries Rj and R5, and lower crust between boundary R5 and Moho discontinuity Rm. The upper crust has a lower velocity of <6.20km/s, and is composed of 4 layers besides the Mesozoic and Cenozoic sediments. The first layer near the surface (above boundary R|) is complex rocks, and the second is deduced as the Utralhigh-Pressure Metamorphic layer. A low velocity layer with a lower Poisson’s ratio of 0.23-0.235 is found between the UHP layer and boundary R3, and it probably implies a detachment or metamorphic granite intrusives. The middle crust between the boundaries Rt and R5 is of a velocity of 6.40km/s, maybe a composition of granulite or amphibolite. The velocity in the low crust is 6.60km/s with a Poisson’s ratio of 0.265, and is of the characteristic of granulite. -The UHP layer takes geometry of an uplift in NS direction, becoming deep in west and shallow in east, and the depth beneath the CCDD is 2.4km with a thickness of 2.1km. The low velocity layer is 2.0km around under CCDD. The uplift is also can be found in the middle crust, corresponding to the UHP belt.The crustal thickness is 31km with an average P-wave velocity of 6.30km/s.5. The crust in Dabie UHP erogenic belt is composed of three layers without low velocity layer, according to the comprehensive research of geological and geophysical data. The shallow velocity has an obvious variation near Huoshan with a lower velocity in the north and a higher in the south. The first boundary depicts a shape of clear vertical offset there. The middle crust and lower crust are both characterized as a更多还原