【作者】 李传友；

【导师】 张培震；

【作者基本信息】 中国地震局地质研究所 ， 构造地质学， 2005， 博士

【摘要】 青藏高原的隆升及其现今的构造活动被认为是正在进行中的印度和欧亚之间大陆碰撞的结果。围绕这一碰撞导致的变形在大陆内部的吸收和调节提出了诸多的模式和理论，分别强调了不同的陆内构造变形方式。“地壳增厚”和“大陆逃逸”假说是长期以来关于大陆内部变形的最主要的两种观点。印度大陆的向北推挤造成的南北向缩短主要被两个过程吸收：(1)逆冲和地壳变厚作用，造成了区域高地形；(2)走滑断裂作用，吸收了大陆块体的侧向位移。这两种模型对于这两个过程在大陆碰撞中的作用和吸收会聚的量存有明显的争议。 青藏高原与周边地区主要断裂带的晚第四纪构造变形及其滑动速率的定量化研究是理解其运动学特征及其动力过程的基础，是帮助解决上述争议问题的关键。 一、西秦岭北缘断裂带晚第四纪活动的微地貌响应及古地震事件 西秦岭北缘断裂带是青藏高原地区大型走滑活动断裂带中的一条，位于青藏高原东北部，由一条主干断裂带和若干条次级断裂组成。该断裂带晚更新世以来以左旋走滑为主，兼有倾滑分量。水系位移是断裂带上最普遍的一种现象。断裂带的水平位移量最大约为300-500m，未见更大的走滑位错的证据。断裂晚更新世晚期以来的位移量最大为40-70m，最小为6m、7m，可能是一次滑动事件的位移量。断裂带第四纪以来表现为分段活动的特点，武山断裂和黄香沟断裂构成了西秦岭北缘断裂带的主体。晚更新世晚期以来，断裂带有过多次强烈活动，活动期次明显。 断裂带在黄香沟一段活动性强，活动现象最为典型。通过黄香沟段横穿断裂带的沟谷及与其相关的地貌和沉积的分析，结合1/10000地质填图和全站仪绘制的大比例尺地形图，对西秦岭北缘断裂带黄香沟段的展布情况、沉积建造、地貌、地质体、晚第四纪位移量等开展了调查与研究。周期性断塞塘淤积和洪积扇变形等微地貌是黄香沟段的一大特征。利用组合型探槽对4个断塞塘进行了三维解剖，通过揭露断塞塘地层剖面分析断裂附近断塞塘的沉积建造特征，讨论与其相关的断裂活动的关系，并且对揭露的沉积进行定年。 1．断塞塘沉积韵律特征与沉积序列 a．垂向特征：从探槽揭露的断塞沉积剖面看，断塞塘的沉积层序均呈现出很好的韵律性，每个断塞塘都包含了几个沉积韵律。一个沉积韵律组合由下部的粗粒层与上部的细粒层组成，粒度下粗上细。b．横向变化：平行断裂走向不同期次的断塞沉积中心的位置呈现规律性的变化，或者说迁移。 2．断塞塘形成机制及与断裂活动的关系 当与断裂相交的水系、山脊发生水平扭动和位错时，在伴有垂直位移和其他地貌效应的情况下，被位移的山脊、河谷壁或者产生的断裂陡坎会阻碍被断裂横切的水系，或迫使冲沟发生肘状弯曲，形成局部阻水或储水的条件，形成了断塞塘。在同一地点多次这样的走滑运动发生，就形成多次断塞作用。 3．断塞塘的断裂作用模式 分析认为，断塞塘中的沉积韵律是与断裂周期性活动相关的。断裂在长期活动中，当应变积累到一定程度，会发生突然快速地运动，之后又进入相对平静期。这导致了断塞塘中的下部粗粒和上部细粒的韵律沉积。断裂多次这样的活动，就形成了几个韵律组成的沉积序列。更多还原

【Abstract】 The rise of the Qinghai-Tibet Plateau and the current tectonic activity on it is regarded as the consequence of the collision being in progress between India and Eurasia, Various models and theories to explain the accommodation of the deformation in continent caused by the collision have been proposed, which emphasize different modes of continental deformation. "Crust Thickening" and "Continent Escape" are two most important ones among the models on continental tectonic deformation. North-south shortening induced by the continuous northward push and pressure of the Indian plate is absorbed by two dominant progresses: thrusting and thickening of the crust, responsible for the high topography of the region; and strike-slip faulting, accommodating lateral displacements of continental blocks. Concerning the relative importance during the collision and the proportion in absorbing convergence of the two processes in these two models are still controversial.Quantitative studies of late Quaternary tectonic deformation and slip rates on the main faults in Qinghai-Tibet Plateau and adjacent area is fundamental to understand its kinematic features and dynamic process, and thus essential to help settling the argument mentioned above.1. Microgeomorphology related to the activity of the Western Qinling Fault Zone and Paleo-seismic events along the faultTogether with the Haiyuan and the Kunlun faults, the Western Qinling Fault is one of the main left-lateral strike-slip fault zones in northeastern Tibet, which elongates as one major trace composed of several segments. The fault zone shows dominant sinistral movement, and partly dip-slip component in late Pleistocene. Displacement of the water systems is a widespread phenomenon along the fault zone. The maximum cumulative horizontal displacement of the fault zone is about 300-500m, displacement larger than this is not observed. The maximum horizontal displacement since the late of late-Pleistocene is about 40-70m, and the minimum is 6-8m. 6-8m maybe is the amount of one principal slip associated with one large event. The fault zone behaves differently in segments, and the Wushan fault and the Huangxianggou fault are two main segments of the fault zone. The fault zone has been intensely active since late Pleistocene.The behavior of the fault zone shows typical strike-slip movement at Huangxianggou. Based on the analysis to the gullies across the fault and the related sediments and landforms, and 1/10000 geologic mapping and large-scale relief mapping, we have investigated the stretch of the Huangxianggou segment, the sediments construction, geomorphology, geologic bodies, and the amount of the slip in late Quaternary, etc. The microgeomorphology such as periodic sag-ponding deposition and deforming of pluvial fans is a major feature in the Huangxianggou segment. The sag-ponding depositions were disclosed by 3-D excavation. Based on the analysis to the profile of the stratum and rediocarbon dates of the sediments exposed by the excavation, sediment distribution and characters of the relevant fault were studied, and the relation between the sag-ponding更多还原