Abstract: Influenced by the far-field effect of India-Eurasia collision, Tianshan Mountains is one of the most intensely deformed and seismically active intracontinental orogenic belts in Cenozoic. The deformation of Tianshan is not only concentrated on its south and north margins, but also on the interior of the orogen. The deformation of the interior of Tianshan is dominated by NW-trending right-lateral strike-slip faults and ENE-trending left-lateral strike-slip faults. Compared with numerous studies on the south and north margins of Tianshan, little work has been done to quantify the slip rates of faults within the Tianshan Mountains. Therefore, it is a significant approach for geologists to understand the current tectonic deformation style of Tianshan Mountains by studying the late Quaternary deformation characteristics of large fault and fold zones extending through the interior of Tianshan. In this paper, we focus on a large near EW trending fault, the Baoertu Fault (BETF) in the interior of Tianshan, which is a large fault in the eastern Tianshan area with apparent features of deformation, and a boundary fault between the central and southern Tianshan. An M_S5.0 earthquake event occurred on BETF, which indicates that this fault is still active. In order to understand the kinematics and obtain the late Quaternary slip rate of BETF, we made a detailed research on its late Quaternary kinematic features based on remote sensing interpretation, drone photography, and field geological and geomorphologic survey, the results show that the BETF is of left-lateral strike-slip with thrust component in late Quaternary. In the northwestern Kumishi basin, BETF sinistrally offsets the late Pleistocene piedmont alluvial fans, forming fault scarps and generating sinistral displacement of gullies and geomorphic surfaces. In the bedrock region west of Benbutu village, BETF cuts through the bedrock and forms the trough valley. Besides, a series of drainages or rivers which cross the fault zone and date from late Pleistocene have been left-laterally offset systematically, resulting in a sinistral displacement ranging 0.93~4.53km. By constructing the digital elevation model (DEM) for the three sites of typical deformed morphologic units, we measured the heights of fault scarps and left-lateral displacements of different gullies forming in different times, and the result shows that BEFT is dominated by left-lateral strike-slip with thrust component. We realign the bended channels across the fault at BET01 site and obtain the largest displacement of 67m. And we propose that the abandon age of the deformed fan is about 120ka according to the features of the fan. Based on the offsets of channels at BET01 and the abandon age of deformed fan, we estimate the slip rate of 0.56mm/a since late Quaternary. The Tianshan Mountains is divided into several sub-blocks by large faults within the orogen. The deformation in the interior of Tianshan can be accommodated or absorbed by relative movement or rotation. The relative movement of the two sub-blocks surrounded by Boa Fault, Kaiduhe Fault and BETF is the dominant cause for the left-lateral movement of BETF. The left-lateral strike-slip with reverse component of BETF in late Quaternary not only accommodates the horizontal stain within eastern Tianshan but also absorbs some SN shortening of the crust.

Key words: Baoertu fault zone, geomorphic features, fault movement property, formation mechanism

摘要： 对天山内部大型断裂带晚第四纪以来的运动学特征进行研究是全面认识天山现今构造变形样式的重要途径。包尔图断裂是东天山内部的一条大型断裂，通过遥感影像解译、无人机摄影测量以及野外地质地貌调查对包尔图断裂晚第四纪的运动学特征进行了研究，发现该断裂在晚第四纪为左旋走滑-逆冲的运动性质。包尔图断裂错断了库米什盆地西北缘山前晚更新世以来的冲洪积扇，地貌上主要表现为断层陡坎、地貌面及冲沟的左旋位错。基岩山区一系列跨过该断裂且形成于中更新世的水系发生了系统性的左旋位错，形成了0.93~4.53km的左旋位错量，表明断层长期活动。通过对山前3处典型变形地貌面建立高精度数字模型，精确测量了不同时期冲沟的左旋位移量及陡坎高度，结果表明断裂以左旋走滑为主并兼有逆冲分量；博罗可努-阿齐克库都克断裂（博-阿断裂）、开都河断裂和包尔图断裂所围限的2个次级块体的相对运动是包尔图断裂左旋滑动的主要原因。包尔图断裂以左旋走滑为主兼具逆冲的运动特征不仅对调节天山内部的水平方向变形有重要作用，同时还吸收了一定的SN向缩短变形。

关键词: 包尔图断裂, 地貌特征, 运动性质, 成因机制