秦岭北麓断裂带晚第四纪活动的地貌表现

本区地貌特征反映秦岭北麓断裂带的活动特点是：①第四纪以来主要发生垂直运动，其活动性质与程度有差异性、阶段性。第一、二级阶地的形态和年代资料表征秦岭北麓断裂带晚更新世和全新世垂直位错幅度和平均速率。②河流阶地在上升盘出口处高度大，而向上游逐渐减小，反映第四纪以来，秦岭断块山地继续发生由北向南的掀斜运动。③被断层切割的冲洪积扇体的结构和堆积层的产状特征，反映出山麓带多发育铲形断层。

GEOMORPHIC EXPRESSlONS OF THE ACTIVITY ALONG NORTH QINLING PIEDMONT FAULT ZONE IN THE LATE QUATERNARY PERIOD

The geomorphic features. especially the changeable structure of alluvial-pluvial fan and the offset difference of river terraces along the North Qinling Piedmont fault zone, show that there are three characteristics of the fault zone activity between Baoji and Lantian: (1)The main moving type is vertical along the fault since Quaternary Period. its active nature and level are different in space and time. The western and eastern segments in the northern-wall(basin side) of the fault slightly subside and the middle segment greatly goes down relative to the southern-wall (mountain side) in the early Pleistocene. the western and eastern parts inversely rise. but the middle part continues to sink violently in the middle Pleistocene. the western and eastern segments intensely uplift, and the middle segment rises slightly in the late Pleistocene. The characteristics of vertical displacement and average moving rate of North Qinling Piedmont fault zone agree with the active feature of fault segmentation based on the analysis of the first and second terraces which are well preserved and dated by the method of thermoluminescence. (2) The river terraces across the Piedmont fault in the uplift-wall is higher at the exits of the mountain than the parts at the upper reaches of rivers, which reflect that the block of Qinling mountain continues to tilt from north to south since Quaternary Period. (3) The characteristics of alluvial-pluvial fan structure and altitude of deposit bed crossed by fault on both walls of the fault zone show there are a lot of listric faults along the Piedmont.The characterisctics above provide a very important scientific basis for further understanding the forming mechanism of the Weihe fault basin and the Qinling fault block rnountain.