【作者】 王海燕；

【导师】 高锐；

【作者基本信息】 中国地质科学院 ， 构造地质， 2006， 博士

【摘要】 松潘地块北缘的若尔盖盆地位于青藏高原的东北缘,其岩石圈结构变化及其与边缘造山带的构造关系记录着高原向东和东北发展演化的深部信息。若尔盖盆地又处于中国大陆东西及南北构造结合部位,特殊的构造环境使其成为研究中国大陆南北对接及东西转折演化之大陆动力学过程的天然实验室,倍受国际注目。由于松潘地块是我国石油资源开发重新认识的重要新区,作为松潘地块主体部分的若尔盖盆地是研究的重点,急需揭示它的岩石圈内部结构、构造属性,从深部发现资源潜力评价的重要依据。岩石圈的精细结构记录着造山带与盆地的形成过程,其内部的构造几何样式和组合形式反映了构造运动学的发展与演变。因此,要研究盆山构造关系、追踪造山带和盆地的变形过程及动力学,必须揭示岩石圈结构,深地震反射剖面技术是研究岩石圈精细结构最有效的方法。国际地学界公认该技术在揭示一些典型的构造现象方面扮演了其它方法所不可替代的角色。由于国内外没有专门的队伍开展深部地质调查工作,长期以来,深地震反射技术依赖于常规地震勘探处理技术的发展和应用。因而在很大程度上受制于以水平地层和简单地形条件下的地震波传播理论的假设条件。事实上由于深地震反射方法的研究区多集中在山区,地形起伏大,地表地质条件复杂、反射资料信噪比低,地下构造倾角大,常规的地震数据处理方法有很大的局限性。针对深地震反射数据资料的特点,如何建立一种实用的技术及处理流程,处理出高质量的反射图像已成为当前深地震反射实际应用中体现效果的重要环节。本论文认真分析常规处理中存在的问题,针对问题实现了地表基准的动校正和改进的速度分析方法,并根据总结野外监控处理流程和分析对比影响单炮记录的品质因素,经方法和参数的测试工作,最终确定了适合于本工区的处理方法和流程。利用加入新实现的地表基准的动校正方法和改进速度分析方法的处理流程对RH04-1-2深地震反射数据进行处理,得到较真实可信深地震反射时间剖面,为揭示若尔盖盆地与西秦岭造山带岩石圈结构,研究盆山构造关系、盆地周边造山带形成的地球动力学机制、造山作用方式和运动学过程等提供了可靠的地震学证据。本论文的研究内容分为三大部分,第一部分是方法研究。针对深地震数据和深部复杂地质构造的特点,本人分析了常规地震勘探处理技术存在的问题,即动、静校正问题和复杂地表地质和深部构造条件下的速度估计问题。针对所存在的问题实现了适合山区的地表基准的动校正和速度分析方法,并利用理论模型和实例数据证明了改进的方法的有效性和可行性。第二部分是深地震反射数据资料的准备部分和处理。首先了解松潘地块地质与地球物理概况,再根据试验工作确定施工参数和施工方案以保证能采集到高质量的深地震反射数据。并通过野外监控处理和分析对比影响单炮质量的品质因素,了解影响单炮质量的因素为各数据处理环节中处理方法和参数的选择提供依据。最后利用加入改进的动校正方法和改进速度分析方法的处理流程对RH04-1-2测线进行处理,得到深地震反射叠加时间剖面。第三部分是深地震反射资料的地质解释。根据处理得到的深地震剖面显示的反射特征,结合其它地球物理资料(重磁和折射资料)及地质资料,对若尔盖盆地和西秦岭的盆山构造关系及盆山形成的动力学过程进行了探讨。最后简明扼要地给出了本次研究所得到的结论以及存在的问题。通过分析深地震反射叠加时间剖面的反射特征并结合已有地质资料得出以下几点结论:(1)若尔盖地块和西秦岭造山带的深部分界线应该在大水弧形构造的南部边界,CDP约为3790左右(对应的野外桩号为4923.5),位于地表分界线南约7.65km。(2)在RH04-1-2时间剖面上双程走时约为2.5s位置出现的一组似层状的反射震相,为三叠系的底界面,按照2.5s以上的地壳的平均速度小于6.0km/s估算,该界面埋深约为7.0km。根据反射特征认为若尔盖盆地和西秦岭造山带基底为同一属性。(3)在深地震反射剖面上西秦岭和若尔盖盆地的基底、上地壳、下地壳及Moho面具有相似的反射特征,表明西秦岭造山带和若尔盖盆地在地质历史上曾经历同一块体的演变过程。(4)盆山构造关系和动力学过程松潘地块于晚三叠世随着昆仑南缘洋盆闭合,拼接到欧亚大陆南缘,成为其大陆边缘。若尔盖盆地作为其前锋与欧亚大陆发生碰撞。深地震反射时间剖面显示的下地壳明显北倾的反射为若尔盖盆地和西秦岭造山带发生俯冲碰撞提供了可靠的地震学证据。喜山期以来,由于印度板块对欧亚板块的强烈挤压作用,伴随青藏高原的隆起,位于青藏高原东北缘的西秦岭-松潘地块向北运动,同时向东逃逸。在向东运移中产生由北西向南东方向的挤压推覆和走向滑动,形成了上地壳的隆起构造。由于地壳内部深度约18～21km存在一个构造滑脱层,使得地壳变形主要发生在上地壳,而下地壳仍保留着印支期构造运动形成的俯冲和逆冲叠覆关系。更多还原

【Abstract】 The Zoigêbasin situated in the northern margin of the Songpan block is located in the northeastern margin of the Qinghai-Tibet plateau, whose lithosphere structure and relationship to the nearby orogenic belts reveal the evolvement process trending eastward and northeastward of the Qinghai-Tibet Plateau. And it also lies in the joint of the China continental east-west and south-north structures. Owing to its special geological location, the Zoigêbasin has been considered as an important sit to study the geodynamic process of the south-north conjunction and the east-west transformation. As a main body of the Songpan block, the Zoigêbasin is researched principally on account of the Songpan block being a virginal area for oil and gas exploration. The inner lithosphere structures and their attributes may reveal the structure relationship of mountain and basin, trail the geodynamic process of orogens and basins, and inform the existing of oil and gas basins, so it is necessary to disclose lithosphere structure. Deep seismic reflection is a most valid method in studying fine lithosphere structure and revealing some typical structure.A deep seismic profile across the Zoigêbasin and the whole the west Qinling orogen was carried out in the winter of 2004. Because of the complicated surface geological conditions and the unusual reflection with high dips and lateral variation in velocities, the data is characterized by the lower S/N and the anormally higher statics. The data processing is far more difficult and the interpretation of the imagines is also hard. Geoscientists face to the work how to process and imagine the data,reveal the geological deformation and the structure relationship of basin and mountain, and tell the evolution stories.The main work in the paper is to develop new techniques to process the data and do the interpretation of the data imagines. In the paper, the problem in the normal seismic process theory has been pointed out and the new algorithms to solve the problem have been developed. The ameliorated methods of normal movement and velocity analysis that were given in the paper, have been tested. The very good imaging results have been obtained in the processing of the deep seismic reflection data. Furthermore, the geological interpretation of the data has also been done in the paper. The paper gives partly the evolution process of the Zoigêbasin and the west Qinling oregen, and recovers partly the tectonic and structural formation of the Block.The paper is composed with three parts of the research work, the deep seismic data processing algorithm, the data preprocessing and processing work, and the imaging interpretation for the structure evolution and the structure relationship of the basin and the orogen.In the first part, the problems of using normal seismic data processing techniques in the deep seismic data have been analyzed. The new algorithms for NMO and velocity analysis based on topography are described and the effectiveness of the algorithms in the processing is proved with the synthetic models and the deep seismic data. In the second part, the processing flow and procedure are clarified. The processing data includes the synthetic models and the deep seismic data( line RH04-1-2)which acquired in the field. In the third part, the interpretation of the data is described for the geological structures formations and the evolutions of the Zoigêbasin and the west Qinling orogen. The structure relationship and the geodynamic process of formation of the Zoigêbasin and the west Qinling orogen are discussed in the paper based on the seismic stack data and some other geophysical data(such as the gravity data, the magnetic data, and the refraction data) and the geological data. Upon the interpretation of seismic imagines and some other studies, the paper gives some research conclusions as follows.(1)The boundary in depth between the Zoigêbasin and the west Qinling orogen is found on the south edge of Dashui Arc like structure, the exact location is in the CDP No.3790(receiver location No.4923.5). It goes to 7.65km south of the surface boundary.(2)The bottom of Triassic layer is found to be at 2.5s(TWT) on the seismic stack section. It is estimated to be 7.0km in depth with an average velocity of 6.0km/s. The basements of the Zoigêbasin and the west Qinling orogen belong to the same basement according to the analysis of seismic data reflection characteristics.(3)It looks similar for the reflection features of the basement, the upper crust, the lower crust and the Moho in the Zoigêbasin and the west Qinling orogen. This reveals that two geological units ever underwent the same evolution process in the geological stage.(4) The deep seismic reflection section show that there are some strong north-dipping reflections which afford reliable seismic evidences for the collision between the Zoigêbasin and the west Qingling orogen.The west Qinling orogen and the Songpan-Ganzi block moved northward and escaped eastward owing to the strong extrusion of Indian plate and Eurasian plate and the uplifting of the Qinghai-Tibet plateau. Movement eastward brought out thrust-pressure and strike-slip movement from northwest to southeast that resulted in the upwarp structure in the upper crust. Layer deformation occured mainly in the upper crust on account of the structural detachment layer at a depth of 18～21km in the crust, and the lower crust keep the trail of the thrust and subduction in Indiosinian Period.更多还原