青藏高原西缘班公错地区新构造运动特征

摘要

青藏高原西缘的班公错地区是青藏高原西构造结的典型区域,更是研究青藏高原中更新世以来构造活动、地貌演化和环境演变的重要区域.依据野外调查结果,借助卫星遥感影像的解译和数字高程模型地形地貌特征的分析,对该地区的新构造运动特征以及其与地形地貌特征的耦合进行了研究.研究结果显示,研究区地貌分区特征以中大起伏山地(地势起伏度500～2 500 m)地貌为主,平原、台地少有发育;班公错地区断层走向分为近EW向、NW向、NE向和NNE向4组,其中近EW向为主体,断陷盆地多具有拉分断陷特征;区内晚新生代地层发育,尤其第四纪冲洪积物和湖积物广泛展布,并受断层的控制具有线性发育特征,湖积阶地和冲洪积阶地发育,班公错北岸乌奖附近拔湖高度62 m、65 m、98 m的沉积阶地钙质堆积物年龄为(23.8±2.3)、(33.9±4.0)、(78.0±8.0)万年;区内地震频发,1970年以来的40年间,4级以上地震达到303次,其中6级以上强震达到7次.众多地质事实指示该地区的中更新世以来为较强烈的、阶段性快速构造抬升和剧烈的剥蚀作用、动荡的构造环境.%Bangong Lake area in western margin of the Qinghai-Tibet Plateau is a typical part of the western syntaxis, and also is the important region of research on the Qinghai-Tibet Plateau's tectonic movement, geomor-phic evolution and environmental changes since the Middle Pleistocene. Based on the results of geological surveys , by means of the satellite remote sensing image interpretation and the analysis of digital elevation models, this paper mainly studies the brief characteristics of neotectonics and its coupling with the terrain and geomor-phic features of the area. The results indicate that Bangong Lake area's faults can be divided into four groups which are nearly EW, NW, NE and NNE, in those, nearly EW is the main fault, and most of these fault basins have the features of pull-apart. Late Cenozoic stratigraphy grows in the region, particularly the Quaternary alluvial-diluvial fans and lake sediments widely distribute, which are linearly developed and controlled by the faults, and lacustrine and alluvial terraces are also developed, which indicate the period of tectonic uplift in the region. The isotopic ages of calcitic sediments are (238 ±23) kaBP, (339 ±40) kaBP, (780 ±80) kaBP on the terraces with heights of 62 m, 65 m and 98 m above lake level near Wujiang at the north bank of Bangong Lake. The earthquakes occurred frequently in this area. According to the statistics, the magnitude of 303 earthquakes are more than Ms 4. 0 and 7 earthquakes of those are more than Ms 6.0 since 1970. The topography and geomorphology characteristics of the study area are mainly middle-large undulating mountain (500-2,500 m terrain undulation). Plains and plateaus also less developed, which indicates that the stronger erosion of surfaceleveling process associating with the crust tectonic uplift since the Middle Pleistocene.