【作者】 潘家伟；

【导师】 李海兵；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2008， 硕士

【摘要】 西昆仑山位于青藏高原西北部,塔里木盆地南缘。新生代以来,印度板块与欧亚大陆的持续碰撞作用造就了西昆仑山脉,在西昆仑山前形成一系列的逆冲褶皱变形和大型逆冲、走滑构造。山前发育的典型构造地貌记录了青藏高原西北部隆升和扩展过程的信息。本研究通过卫星影像解译、DEM数据处理和大比例尺地形图分析,结合野外地质、地貌和构造变形特征的观察与测量,对该地区的构造地貌进行了定性和定量的研究,对山前冲断带的结构、构造特征及扩展过程,前缘逆冲位置及西昆仑山新生代以来的隆升速率和山前构造缩短量进行了初步的研究,取得如下认识:(1)在青藏高原西北缘存在着两级夷平面:山顶面和主夷平面,并且由于区域隆升作用的不一致性,即西昆仑隆升的空间差异性造成两级夷平面的高度在西昆仑山东段和西段有所差别。在西昆仑山东段及阿尔金地区,山顶面海拔5800～6400m,主夷平面5200～5800m;在西昆仑山西段及帕米尔地区山顶面海拔5000～5200m;主夷平面海拔4000～4500m。(2)西昆仑山前发育的一系列典型构造地貌特征记录了西昆仑山的隆升和山前冲断带在新生代强烈活动的信息,同时构造地貌特征表明西昆仑山前冲断带在由南向北逆冲、扩展的过程中存在着由西向东的迁移特征。(3)通过对山前固满背斜、英吉沙背斜形成时代和变形量的研究,初步估算了西昆仑山新生代时期的隆升速率:晚上新世-早更新世以来的最低隆升速率为0.21～0.25mm/yr;中更新世以来的隆升速率约为0.23mm/yr,两者速率接近一致,这暗示着在晚上新世-中更新世这段时期内西昆仑山可能存在一个缓慢的匀速隆升过程。而对山前河流阶地形成时代和隆升高度的研究表明晚更新世以来西昆仑的隆升速率约为1.5mm/yr,这说明至少从晚更新世开始西昆仑山的隆升速率开始加快,可能存在一个快速的隆升过程。(4)根据剖面面积平衡的原理,计算出西昆仑山前固满背斜和英吉沙背斜的水平构造缩短量分别为300m和108m,并参考前人的年代数据,估算出固满背斜晚上新世-早更新世以来的平均缩短速率约为0.14～0.17mm/yr,英吉沙背斜在中更新世以来的平均缩短速率约为0.11mm/yr。(5)西昆仑山前由南向北的逆冲作用伴随走滑分量,乌泊尔断裂在由南向北逆冲过程中伴随较大的右旋走滑分量,该断裂的右旋走滑作用错断了古近纪地层及流过断裂的河流。通过测量单次地震造成的水系错断量并参考前人研究的该地区大震复发周期约为1000年,估算出该断裂的平均走滑速率为4～6.8mm/yr,并推测断裂开始活动的时间大约在2.2～3Ma以前。(6)在西昆仑山与天山之间的喀什地区,通过详细的野外考察和测量,厘定出帕米尔东北缘西昆仑山山前逆冲前缘和西南天山山前逆冲前缘的位置。前人认为属于西南天山山前逆冲系统的明尧勒背斜、喀什背斜实际上为帕米尔东北缘西昆仑山山前冲断带的最前缘,而北侧的阿图什-踏浪河背斜是西南天山山前冲断带的最前缘。该地区以西,帕米尔东北缘西昆仑山和西南天山西大构造系统已经发生了碰撞和拼贴。(7)塔里木盆地中麻扎塔格地区的地貌和地表变形特征均指示出该地区存在南南向北的逆冲作用,同时深部的地球物理资料也显示出麻扎塔格断裂由南向北逆冲的特征,结合大的区域构造特征,认为麻扎塔格逆冲断裂为西昆仑山前冲断带的前缘部位,和田河气田处在逆冲前锋背斜顶部,其逆冲最前沿可能还要向北推进。新生代变形作用已明显地改造了塔里木盆地南部及中部的古生代和中生代构造,虽然和田河气田处在石炭系中,但有可能是新生代强烈的构造变形作用促成了气田的形成。更多还原

【Abstract】 West Kunlun Mountains locate in the northwestern Tibetan plateau, southern margin of Tarim basin. The continuous collision of Indian plate and Euro-Asia plate since Cenozoic era formed the West Kunlun Mountains. This process also resulted in a series of deformation and large-scale strike-slip and thrust faults along the mountain front. The typical morphotectonics of the piedmont recorded the uplift and propagation information of the northwestern Tibetan Plateau.Based on the interpretation of satellite images, processing of DEM data, analysis of large scale topographic maps, combined with field morphotectonic investigations and observations, a qualitative and quantitative morphotectonic features of this area was investigated. Typical features such as the structure, tectonic and propagation process of the thrust belt in the piedmont of West Kunlun, the location of the frontal thrust zone, the uplift rates of the western Kunlun Mountains since Cenozoic and the shortening amounts of the piedmont structural belt was also studied. Some cognitions are presented as follows:(1) There are two planation surfaces: summit planation surface and main planation surface in northwestern Tibetan plateau. The inconsistencys of the regional uplift process result in the different heights of planation surfaces between the east part and western part of western Kunlun. At the east part of the West Kunlun, the altitude of the summit planation surface and the main surface are 5800-6400m and 5200-5800m respectively; At the west part of the West Kunlun, the altitutude of the planation surface and the main surface are 5000-5200m and 4000-4500m respectively.(2) A series of typical morphotectonic features of West Kunlun piedmont record information about the uplift process of the west Kunlun and intense activity of the thrust belt in the piedmont of West Kunlun. These morphotectonic features also indicate that the West Kunlun piedmont migrated from west to east in the process of its propagation.(3) Based on study of the formation age and deformation amount of the Guman Anticline and the Yingjisha Anticline, the uplift rates of the West Kunlun during the Cenozoic were alculated: The minimum uplift rates were 0.21-0.25 mm/yr from late Pliocene-early Pleistocene and 0.23mm/yr from middle Pleistocene. These two rates are similar, indicating that a slow and uniform uplift process might be exist of West Kunlun from late Pliocene to middle Pleistocene. The study on the formation ages and the uplift heights of the piedmont river terrace shows the uplift rate of the West Kunlun Mountain was 1.5mm/yr from the late Pleistocene, this indicates that the West Kunlun uplifted more quickly from late Pleistocene.(4) By the area-balance theory, shortening amount of Guman Anticline and Yingjisha Anticline in the piedmont of West Kunlun are calculated, which are 300m and 108m respectively. Based on the previous data, it is estimated that the average shortening rate of Guman Anticline ranges 0.14-0.17mm/yr since the Late Pliocene-Early Pleistocene and the average shortening rate of Yingjisha Anticline is about 0.11mm/yr since the Middle-Pleistocene.(5) The south-vergent thrusting in the piedmont of West Kunlun has a strike-slip component. The thrusting of Upar Fault accompanied by a large right-lateral strike-slip component, which offsets the Paleogene and rivers that flow through the fault. According to the measured offset of drainages caused by single earthquake event and pervious research that the recurrence interval of large earthquake is about 1000 years, the average strike-slip rate of the fault is estimated as 4-6.8mm/yr, and the fault is estimated to start at 2.2-3Ma.(6) Based on detailed field survey and measuring work in Kashi area located between West Kunlun and Southwestern Tianshan, the locations of the thrust front in the piedmont of the West Kunlun and the Southwestern Tianshan are located. Mingyaole Anticline and Kashi Anticline are the most forefront of thrust belt in the piedmont of West Kunlun and Atushi-Talanghe Anticline are the most forefront of thrust belt in the piedmont of Southwestern Tianshan. The two large tectonic systems of West Kunlun and Southwestern Tianshan have collided in the west of this region.(7) Both the morphotectonics and surface deformation of the Mazartagh in Tarim basin indicate that south-vergent thrusting exists, and deep geophysical data also show the south-vergent thrusting of the Mazartagh fault. Combination with regional tectonics, the Mazhatage thrust fault is considered as forefront of the thrust belt in the piedmont of West Kunlun. Hetianhe gasfield located on the top of anticline in the front of the thrust, and the forefront of the thrust may exist northward. Deformations in the Cenozoic have obviously changed the structures of the Palaeozoic and Mesozoic in the southern and middle of the Tarim basin. Although Hetianhe gasfield locates in the Carboniferous, intense deformation in the Cenozoic promoted the formation of the gasfield.更多还原