东昆仑断裂东端塔藏断裂压剪活动与高原隆升作用讨论

Discussion on the Compression-Shear Activity of the Tazang Fault in East Kunlun and Uplift of Plateau

塔藏断裂位于东昆仑断裂带东端,横贯青藏高原东缘的高原内部和边缘,因属于巴颜喀拉块体向东南运移的东北侧边界带,其晚第四纪活动性质和滑动速率对认识青藏高原的构造变形模式极端重要。本文综合SPOT、中巴资源卫星等高分辨率遥感影像解译,利用冲沟、山脊、断错河流阶地、断层槽谷、反向坎等地震地貌的识别,开展详细的断错地层、地貌研究和系列年代学样品采集测试,对塔藏断裂的精细几何展布、晚第四纪活动性质、滑动速率进行详细分析。塔藏断裂自西向东可分为青藏高原内部的罗叉段、青藏高原边缘的东北村段和马家磨段,各段走向依次为113°、142°、130°,逐渐向南偏转,晚第四纪的活动表现为分段性和多期性。罗叉段全新世以左旋剪切走滑为主兼挤压活动,左旋走滑速率为2.43~2.89mm/a左右,最新地表断错事件发生在0.66±0.04ka BP以来,断层面表现出走滑断层的近垂直和张裂并发育充填楔的典型特征,塔藏断裂为东昆仑断裂系东延的主要断裂之一;马家磨段也为全新世活动断层,距今9.0±0.8ka的地层被断错,而且断层面北倾达58°。因此,对比分析塔藏断裂各段活动特征可见,西部以水平剪切运动为主,而东部走滑运动分量逐渐变弱,断面北倾、北盘上升导致的垂向分量逐渐变大。东昆仑断裂带及塔藏断裂晚第四纪走滑速率向东规则减小,并转化为横向逆冲作用和高原隆升,符合"叠瓦状逆冲转换—有限挤出模型"的特征。

Tazang fault in the eastern section of East Kunlun fault traverses the interior and boundary of the eastern margin of the Qinghai-Tibet plateau. As the northeastern boundary of the southeastward movement of Bayankala terrane, its active features and sliding rate in Late Quaternary are extremely important to understanding the tectonic deformation of the Qinghai-Tibet plateau. Combined with interpretation of the high-resolution remote sensing images obtained through SPOT and ASTER DEM, this study carried out detail research on offset strata and landform and geochronology using seismic data and morphological features （such as streams, mountain ridges, displaced fluvial fans, terrace, fault valley, reversed camp, and so on）, so as to understand the distribution, activity and strike-slip rate of the Tazang faults in late Quaternary. The Tazang fault can be divided into from west to east. Luocha section in the Qinghai-Tibet plateau, Dongbeicun section and Majiamo section in the margin of the Qinghai-Tibet plateau, with each section trending to 113°, 142° and 130° respectively, and gradually turning toward south. Its activity in late Quaternary is characterized by multiple stages and episodes. The Luocha section was dominated by sinistral shear strike-slip in company with compression during Holocene, with a sinistral strike-slip rate of 2.43±2.89 mm/a. Since 0.66 ±0.04ka BP when the latest offsetting event occurred, the fault surface is characteristic of nearly vertical strike slipping and well-developed tensional filled fractures. The Tazang fault is one of the major faults in the eastern extension of the East Kunlun fault system. The Majiamo section may be the active fault in Holocene, and 9.0±0.8ka stratum was faulted, with the fault surface dipping north up to 58°. Therefore, comparative analysis of activities of each segment in the Tazang fault shows that the western section was predominantly horizontal shear movement, the eastern section had a decreasing strike-slip motion component, and north-dipping of fault surface and uprising of northern hanging wall both resulted in gradually increasing of the vertical component. Strike- slip of East Kunlun fault zone and Tazang fault tended to decrease eastward in late Quaternary, and was converted into horizontal thrusting and plateau uplift, which is consistent with the features of the ＂imbricated thrust conversion- limited extrusion＂ model.