【作者】 肖骑彬；

【导师】 赵国泽；

【作者基本信息】 中国地震局地质研究所 ， 地质学， 2006， 博士

【摘要】 本研究旨在利用已有大地电磁(MT)及最新测得的长周期及常规MT资料,采用先进的资料处理与解释技术,研究得到较可信的大别-苏鲁造山带的地壳-上地幔的电性结构。结合前人的地质研究成果等,发挥大地电磁方法的优势,针对大别—苏鲁造山带研究的热点问题或者有争议的问题进行综合研究,例如:关于大别-苏鲁造山带缝合线、各地块边界、主要断裂的位置和深部延伸状况;扬子地块、造山带和华北地块的深部接触关系和可能的相互作用;岩石圈可能的物质状态;高压-超高压变质带的深部位置及其和围岩的关系;高压-超高压变质岩折返的深部过程、造山带的演化和动力学过程等。首先,介绍了大地电磁测深资料解释过程中经常遇到的问题,对畸变与静位移的原理与常见的解决方案、不同二维反演方法的优缺点、在二维反演中误差及极化模式的处理方式等进行了简要探讨。其次,以大别造山带为重点,先对造山带的基础地质及其与秦岭造山带的差异进行了介绍与分析;再利用已有的MT资料,在大别造山带沿NE28o布置的三条大地电磁测深剖面,采用非线性共扼梯度法分别对三条测线作二维反演,获得了关于大别造山带的地壳上地幔二维电性结构。以二维电性结构为基础,通过插值处理组建三维模型,利用交错网格有限差分三维正演程序求得模型的电磁响应,所得的视电阻率和相位曲线与原始数据在曲线形态上具有较好的一致性,从而进一步验证了二维电性结构的可靠性。从测区不同深度电性水平切片来看,从上地壳到下地壳到地幔尺度,电性结构走向具有从近东西向到近南北向的过渡,表明造山带下地壳及地幔物质经历过主造山期后的流变调整。从三条剖面的电性结构总体上看,垂向上可分为四层,地表覆盖层、中上地壳相对高阻层、壳内相对低阻层,地幔;横向上,北淮阳与大别地块是电性差异显著的构造单元,它们之间以晓天-磨子潭断裂分隔,晓天-磨子潭断裂总体倾向北,延深至上地幔。在大别地块内中、上地壳高阻层最厚处在罗田-蕲春-英山-岳西一带,大别地块在电性结构上应是一个整体,不支持南、北大别之分;在大别地块内,推测存在早期岩浆活动的通道,它们对大别地块内存在的中、下地壳高导层有破坏改造作用,后者在层位上相差较大。并对大别造山带的演化动力学模式进行了探讨。最后,对最新在苏鲁造山带获得的一条大地电磁测深剖面资料进行了解释,剖面沿SE129o,西起华北地块,跨郯庐断裂带、苏鲁超高压变质带、高压变质带,止于扬子地块。通过对资料的定性分析,二维性判别以及极化模式的识别,选择非线性共扼梯度法,用TE+TM联合模式下进行二维反演,得到了关于测区地下200km以上的电性剖面,具有较好的可靠性。通过对电性剖面的分析,在横向上,沿剖面自西而东,划分出了七个电性分区,其中对郯庐断裂带、海州-泗阳断裂以及嘉山-响水断裂等重要的边界断裂的深浅展布与延伸进行了很好的限定;纵向上,对剖面深度划分出六个电性层,初步分析了可能的深部物质状态。发现了在华北地块与扬子地块内存在着壳内的高导层,而造山带下部没有发现高导层,这一点与大别造山带存在较大的差异。发现了在50-90km之间层位,存在较连续的相对低阻带,推测为岩石圈上部的软弱带,可能指示造山带下部不同地块间发生过相对运动。最后认为在超高压变质岩形成期后,华北地块有较强的向南推挤作用,这种推挤作用的驱动力是发生在岩石圈尺度,在地壳层次表现为一系列的推覆及韧性剪切构造,在岩石圈深部,扬子地块的岩石圈则被动地向后收缩变形,而壳幔深部岩石层间的相对运动产生了岩石圈上部的软弱变形带。更多还原

【Abstract】 In the study, the existent magnetotelluric data and the latest data of long period and normal MT are used, with advanced data-processing technique, we provide rather reliable electrical structure of crust-upper mantle in Dabie-Sulu orogen. Combining with the basic geology and using the advancement of MT, we emphasize our study on the following: the suture in Dabie-Sulu orogen, the boundary of each block, the location and extending status in depth of main faults, the contact relation in depth and possible interaction of Yangtz block, orogen and North China block, the possible status of lithosphere, the situation in depth of HP-UHP metamoprhic zone together with the relation with the wall rock. So to speculate on the exhumation procedure of HP-UHP metamorphic rock in depth, the dynamic procedure of orogen’s evolvement, addtionally, to provide geophysical evidence for orogen study.Firstly, some frequently encountered problems in the process of MT data-interpreting are proposed, together with a brief discussing of the theory of distortion and static shift with their mostly used settlement, the advancement and disadvantage of two-dimensional inversion methods, the disposal methods of error and polarization mode in two-dimensional inveriosn.Secondly, emphases are on Dabie orogen, after a brief introduction and analysis of the basis geology between Dabie and Qinling orogen, with the existent MT data, three profiles in Dabie orogen are designed, the profiles, across the high-ultrahigh pressure metamorphic belt, were in NE28o directions.With 2D inversion program of Non-linear conjugate gradient method, three profiles’two-dimensional electrical structures of crust-upper mantle of Dabie orogen are obtained. Based on the two-dimensional electrical structures, a 3D model is made by Kringing interpolation. Then, the model’s electromagnetic responses are computed with 3D finite difference forward program, the response apparent resistivity and phase curves coincide with the observed data well. So to say, the 2D inversion results are reliable. From the electrical plane slice of different depth in Dabie orogen, the strike of electrical structure shows a transition from nearly EW to SN direction with the depth increasing. It indicates that the materials of lower-crust and upper-mantle under Dabie orogen have experienced post-orogeny rheological adjustment. The 2D electrical structures of three profiles are comparable, and can be divided into four layers in vertical direction, that is, the surface cover layer, the mid-upper crust high resistivity layer, the inner crust relatively low resistivity layer and the mantle. In horizontal direction, The North Huaiyang Tectonic Belt and Dabie Block are different tectonic units in electrical structure, they are separated by Xiaotian-Mozitan fault, which dips north and extends downto the upper mantle. In Dabie Block, the thickest place of the mid-upper crust high resistivity layer is along Luotian-Qichun- Yingsan-Yuexi. The Dabie Block is of massive structure in electricity, it does not support the division of North and South Dabie. In Dabie Block, there maybe exist channels of granitic magma activity of Jurassic and Cretaceous period, which make further uplift of the Ultra-high pressure metamorphic rocks and affect the distribution of inner-crust high conductive layer and cause great difference in depth of the high conductive layer. At the end of this chapter, the dynamic model of Dabie orogen’s evolvement is discussed.更多还原