【作者】 陈正位；

【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， 2013， 博士

【摘要】 强烈的缩短构造变形使天山北麓地壳掀斜抬升，大规模的洪积砾石层和黄土堆积增加了地表高程，干旱化条件下局限在狭谷河道的下切使山麓地表总体保持稳定，在不同时间尺度上的构造变形与气候变化的共同作用下，天山得以向北扩展，继续着造山过程。天山北麓地壳有两种垂直方向上的变形方式，一是准噶尔南缘断裂带的逆冲推挤，二是岩层沿底部滑脱面向北运动，同时发生逆断裂和褶皱；由此天山北麓地壳自南向北掀斜抬升。在近东西向的水平方向上，第一排逆断裂‐褶皱带的清水河‐石梯子断裂仍在向西扩展，在地表上形成隆起；第二排逆断裂‐褶皱带的霍尔果斯褶皱、玛纳斯褶皱、吐谷鲁褶皱由中部开始，逐步向两侧扩展，最终连接成统一的褶皱隆起；第三排逆断裂‐褶皱带的独山子褶皱、哈拉安德褶皱、安集海褶皱也是由中部开始向两侧扩展，形成了三个孤立的褶皱隆起。由于准噶尔盆地地壳沿南东方向上向天山地壳的斜向俯冲和多层次消减，造成天山北麓地壳浅部岩层以褶皱和逆断裂的形式沿北西方向扩展。上游汇水盆地和下游洪积扇是一个耦合系统，中更新世以来，冰川剥蚀形成的大量松散物质贮积在山间，当遇到间冰期、间冰段、高温大降水等暖湿时期，山间松散物质搬运至主河道，并逐步搬运到山麓，形成洪积扇，组成了山麓堆积。由于中更新世以来持续的干旱化，坡麓地表径流小，剥蚀轻微，河流下切局限在狭谷式的深切河道中时行，侵蚀只占坡麓地表面积的10%，总体上地表比较稳定。天山北麓被逆断裂和褶皱隆起分隔为分隔盆地，一方面，各个分隔盆地面以阶梯式整体掀斜抬升；另一方面，变形隆起在分隔盆地前缘形成阻挡，使碎屑物质容易在分隔盆地中堆积下来，增加了盆地面的高度；由于地表剥蚀轻微，抬升和加积增高全部转换为地表隆起。随着地壳缩短，山前的构造隆起逐步缩短与天山之间的距离并与天山拼贴在一起，成为天山的一部分；同时由于构造隆起的向北扩展，准噶尔盆地南缘自南向北逐渐隆起成为山脉的一部分，天山得以向北扩展。天山北麓奎屯河的河流下切表明，河流下切是长时间尺度上的构造变形和干旱化，以及短时间尺度上的湿润气候变化共同作用的结果。长时间尺度上的构造变形为河流下切提供了坡度，而短时间尺度上的气候变化为河流下切提供了额外的水动力。末次冰期期间始于～30ka的高温大降水，水动力增强，山间物质被搬运到山前形成洪积扇，而后河流供给物减少，水动力主要用来下切河床，洪积扇被下切形成T3阶地。全新世早期～11ka是末次冰期之后的高温降水期，松散物质从奎屯河冲出来堆积在T2阶地的基座上，而后松散物质供给减少，在～10ka开始下切形成T2阶地。全新世以来，在越来越干旱的背景下，地表径流减小，松散物质难以搬运到下游，水动力几乎全部用来侵蚀河床，河流下切更为强烈；湿润期到来时，少量松散物质搬运到下游堆积下来，湿润期结束后，地表径流减小，河流中没有充足的松散物质，河床减小宽度以增强水动力，再次开始下切；因此，全新世以来天山北麓加剧的干旱化是河流强烈下切的主要原因。另外，天山北麓的逆断裂和褶皱变形为河床提供了额外的坡度，为水动力的多次下切提供了坡度条件，在褶皱变形部位形成了多级阶地。更多还原

【Abstract】 Crust of the northern pediment of Tian Shanwas tilted and uplifted from south to north with continuing and intense deformation since middle Pleistocene. Mass ofconglomerates and loess mantled in northern blank of Tian Shan and a large scale of fluvial fan developed to accumulate the elevation of the pediment. With the drier climate, incision was limited in the stiff canyon trenched by the main stream. The surfaces keep a stable statue of equilibrium between incision and accumulation. Tian Shan had propagated to north with the impact by climate change and tectonic deformation in deferent time scale and undergone intercontinental orogeny since middle Pleistocene.Two styles of deformation existed in the crust of northern pediment of Tian Shan on vertical direction. One is thrusting that the crust of Tian Shan overthrusted to the Zhunger basin along the South Zhunger Fault (SZF). The other is the upper layer of rock moved to north along the deep decollement surface and the rock folded and thrusted as the same time. As a result, the crust of the pediment of Tian Shan was tilted and uplifted from south to north. There are three row of folds‐thrusts belts in north blank of Tian Shan. The Qingshuihe‐Shitizi Fault (QSF) in the first row of folds‐thrusts belt propagated to west and made the surface uplift. The Huoerguosi folds, as well as Manas folds and Tugulu folds, of the second rows of folds‐thrusts belt propagated from the middle to the both side. The three folds uplifted and consolidated to a low mountain. The Dushizi folds, as well as Halaande folds and Anjihai folds, of the third rows of folds‐thrusts belt propagated from the middle to the both side. The three folds uplifted to became three isolated mountain. The rock of upper crust in the northern pediment of Tian Shan propagated along the NW direction with the folding and thrusting deformation due to multi‐level subduction that the crust of the Zhunger Basin subducted to the crust of Tian Shan along the SE direction.The catchment and the fan is a coupling system. Mass of loose materials covered the upper catchment. In the warm and humid climate stage, the storage materials in mountain were transported to the main stream and carried to the front of mountain. With repeatedly transporting, the fan was formed. For the drier climate, the runoff was so lack that the surface could be hardly eroded. Consequently, incision was limited in the stiff canyon trenched by the main stream and the incision surface only was10percentage of the whole surface. The surfaces keep a stable statue of equilibrium between incision and accumulation. The pediment of the north Tian Shan was tilted and partitioned several parts by the folds and thrusts. Materials aggraded in the partitioned basins and surface accumulated elevation of the basins. On the other hand, partitioned basins were distorted accompanying with deformation of thrust faults and folds. As a result of shortening, the partitioned basins tilted along the northern flank of Tian Shan. Uplift of crust tilt almost totally converted to uplift of surface because of slight erosion. The pediment near the mountain became higher as a part of Tian Shan. As a result, the Tian Shan propagated to north.Study of downcutting of the Kuitun River shows that intense river downcutting in northern pediment of Tian Shan controlled by tectonic deformation and drier climate change at the long time scale, and also controlled by warm and humid climate change at the short time scale. The slope was supplied by long‐term deformation and the additional river power was supplied by the short‐term climate change. At the stage of high temperature and mass precipitation about30ka B.P. in the Last Glacial period, the stream power increased. The materials in mountain were transported to the northern blank of Tian Shan and formed fluvial fans. With supply of the river sediment decreasing, the stream power was used to downcut river bed. The fluvial fan in middle Pleistocene was entrenched and the terrace T3formed. At the warm and humid climate stage in early Holocene about11ka B.P., the loose materials in the mountain were carried to deposit on the strath terrace. With supply of the river sediment decreasing, the stream power was used to downcut river bed at10ka B.P. and the terrace T2formed. Since early Holocene, the surface runoff strongly decreased with the more arid climate and the storage of loose materials in upper catchment could be hardly carried to the northern front of Tian Shan. Therefore, all of stream power was used to entrench river bed and the river downcutting became more intensely. At the stage of humid in Holocene, small amounts of materials was transported to the downstream and deposited. At the end of humid stage, the river had not enough deposit materials and the width of river bed was decreased to increase stream power. The river became a new stage of downcutting. For the reason, more arid climate change since early Holocene led to intense river downcutting in the northern pediment of Tian Shan. Moreover, the additional slope was supplied by the deformation of folds and thrusts. It increased additional stream power for entrenching river bed many times and a lot of terraces formed where the river crossed the folds.更多还原