LATE QUATERNARY ACTIVITY AND TRANSPRESSIONAL DEFORMATION OF THE KARLIK TAGH NORTH FAULT, EASTERNMOST TIANSHAN

doi:10.3969/j.issn.0253-4967.2022.01.004

Abstract

Abstract:

Karlik Tagh and other lesser ranges of the easternmost Tian Shan are natural laboratory for studying the fault architecture of an active termination zone of an intraplate mountain belt. The Karlik Tagh is located at the easternmost Tian Shan which is active due to the collision of India plate and Eurasian plate in Cenozoic and this range represents the geomorphological and structural end of Tian Shan. Therefore, studying the geometry and kinematics of active faults distributed at this area has important implications for understanding the dynamics features of the end porting of the Cenozoic orogenic belt. This paper is focused on the North Karlik Tagh Fault(KTNF), which is an important active structure at the easternmost Tian Shan. This fault extends about 180km and is gently distributed between the Yiwu Basin and the north of Karlik Tagh. Based on remote sensing and detailed field research, we propose to subdivide the NKTF into 2 segments based on its variation in strike and motion characteristics.
At the west of the NKTF, the west segment is mainly distributed at south of Yanchi County and extends intermittently about 61km. The fault trace along Yanchi segment is obvious and expressed by several linear fault scarps on the foreland alluvial fan surfaces north of Karlik Tagh. Outcrop on a channel wall shows that the fault dips SW and thrusts directly to the NE. Topographic profiles across the scarps have shown that the minimum vertical offset is(1.3±0.5)m, which can be caused by a single earthquake rupture. The maximum vertical offset is(7.3±0.3)m. An OSL dating sample was obtained at 70cm below the T1 terrace surface. And we get the deposition age of(7.0±1.4)ka. Based on the OSL dating of deformed T1 terrace and the vertical displacement of(1.3±0.5)m of T1 and vertical displacement of(2.5±0.2)m of T2, a vertical slip rate of 0.19~0.35mm/a can be calculated. This vertical rate is slightly larger than that of the North Hami Basin Fault, which is consistent with the S-directed tilt of the Karlik Tagh.
At south of Xiamaya town, the east segment of NKTF changes its strike and bends to NE, extending nearly 95km. Toward the east, this fault is connected with the west end of Gobi-Tianshan fault system(GTSFS)at the border of China and Mongolia. There are clear evidences of recent activity of this fault, including well-preserved scarps and offset streams on the alluvial sediments. And this fault segment is very obvious because of linear features on the Google Earth image. About 23km southeast of Xiamaya town, the fault trace runs across a north-flowing river, causing remarkable sinistral offset of the T3/T2 terrace ridge with the maximum displacement of(172±20)m. At about 10km northeast of this river, the NKTF passes through a massif with steep slope on the south and gentle slope on the north. Field observation of a hand-dug outcrop has shown that this fault dips N156°E. In addition, the fault also displays reverse faulting component and dislocates the gravel-bearing silt sedment by about 2.0m.
At north of Karlik Tagh, several NW-trending faults can be interpreted on the satellite image. These faults extend short and form a clear boundary between bedrock and Quaternary sediments. Although there are no obvious deformations in the sediment such as diluvial fans or river terraces in the valley, the good linear characteristics on both sides of the valley indicate that these faults have been active since Quaternary. Because these faults are nearly parallel to the western segment of the northern margin of the Karlik Mountains, and there is no geomorphological evidence of horizontal movement of the faults, it can be inferred that the faults on both sides of the Adak Valley are mainly dominated by vertical movement.
The Karlik Tagh North Fault, together with, the north margin faults of Hami Basin and other NW-trending secondary faults in the north side of Karlik Mountain constitute the horse-tail end structure of Gobi-Tianshan sinistral strike-slip fault system, which regulates and absorbs the sinistral deformation of Gobi-Tianshan fault system and these faults present a positive flower structure in the cross-section. The uplift of Karlik Tagh is controlled by NW thrust fault and NEE left-lateral strike-slip fault, and this range is a typical transpressional mountain in the easternmost Tian Shan.

Key words: North Karlik Tagh Fault, movement feature, transpressional deformation, easternmost Tian Shan

摘要：

喀尔里克山位于天山最东端, 是天山造山带往东地貌和构造的终止端, 研究该地区断裂结构和运动学特征对于全面认识天山新生代变形模式具有重要意义。喀尔里克山北缘断裂呈弧形展布在喀尔里克山北侧, 向E延伸与戈壁-天山左旋走滑断裂系相连。根据其走向和运动性质的差异可将喀尔里克山北缘断裂分为东、西2段, 西段长约61km, 走向NW, 呈逆冲性质, 断裂活动在山前洪积扇上形成了多条断层陡坎。利用光释光测年方法对变形阶地进行定年, 得到西段全新世垂直滑动速率介于0.19~0.35mm/a之间, 该滑动速率略大于喀尔里克山南侧的哈密盆地北缘断裂的垂直滑动速率, 这与山体向S掀斜的地貌特征一致。东段长约95km, 走向NE, 以左旋走滑变形为主, 断裂左旋错断了一系列冲沟和河流阶地, 剖面显示该断裂段还具有一定逆冲分量。喀尔里克山北缘断裂与山体两侧其他逆冲断裂共同构成了戈壁-天山左旋走滑断裂系的挤压性马尾状端部构造, 这些断裂在深部收敛会聚并在剖面上呈现不对称的正花状构造。喀尔里克山体的抬升受南北两侧逆冲断裂和东侧左旋走滑断裂共同控制, 表现为转换挤压变形抬升的特征, 山体通过山前逆冲断裂向盆地内部的迁移逐渐向外扩展。

关键词: 喀尔里克山北缘断裂, 运动特征, 转换挤压变形, 天山东端

CLC Number:

P315.2

REN Guang-xue, LI Chuan-you, SUN Kai. LATE QUATERNARY ACTIVITY AND TRANSPRESSIONAL DEFORMATION OF THE KARLIK TAGH NORTH FAULT, EASTERNMOST TIANSHAN[J]. SEISMOLOGY AND GEOLOGY, 2022, 44(1): 46-62.

任光雪, 李传友, 孙凯. 天山东端喀尔里克山北缘断裂晚第四纪活动与转换挤压变形[J]. 地震地质, 2022, 44(1): 46-62.

Figures/Tables 12

Fig. 1 Structural and geomorphological map around the Karlik Tagh at the easternmost Tian Shan.

Fig. 2 Divisions of frontal morphologic units on east segment of the KTNF.

Fig. 3 Field photos of deformed Late Quateranry deposits along the west segment of KTNF.

Fig. 4 The topography at Bileuteck site on west segment of KTNF(a); Photos of deformed terraces and sampling site(b).

Fig. 5 Topographical profiles normal to the fault scarp at Bileuteck site(see Fig.4a for detailed site location).

Table 1 The result of OSL dating from the T1 terrace on Bileuteck segment

编号	埋深 /m	²³⁸U/Bg·kg^-1	²²⁶Ra/Bg·kg^-1	²³²Th/Bg·kg^-1	⁴⁰K/Bg·kg^-1	含水量 /%	环境剂量率 /Gy·ka^-1	等效剂量 /Gy	年龄 /ka
KAR-OSL-02	0.7	55.8±9.9	32.2±0.9	45.2±1.0	582.9±19.9	4	3.5±0.2	24.4±4.6	7.0±1.4

Fig. 6 Geomorphology of the faulted river terraces at the east segment of KTNF.

Fig. 7 Field photos of deformed landforms on east segment of KTNF.

Fig. 8 Google Earth image of the uplifted massif at south of Xiamaya site.

Fig. 9 Outcrop of the fault and its interpretation on east segment of KTNF.

Fig. 10 Fault distribution around Yiwu and field photo.

Fig. 11 Block diagrams representing the building process of Karlik Tagh(a) and corresponding stages in plain view(b).

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