新疆天山南部北轮台断裂带晚第四纪活动速率

LATE QUATERNARY CRUSTAL SHORTENING RATE OF THE BEILUNTAI FAULT IN SOUTHERN TIAN SHAN,XINJIANG

北轮台断裂是1条全新世活动断裂,为南天山与塔里木盆地的分界断裂。晚第四纪以来,北轮台断裂的持续活动使得多期洪积地貌面发生了断错变形与褶皱隆升。利用高精度差分GPS,对北轮台断裂阿克艾肯段和砖厂段内的多期地貌面的断层陡坎形态进行了测量。通过大比例尺活动断层填图发现,阿克艾肯段以逆冲作用为主,而砖厂段则是以褶皱隆升为主。利用光释光测年方法,分别得到了不同期次地貌面(Fan4,Fan3b,Fan3c和Fan2)的年龄,发现自Fan4地貌面形成以来,阿克艾肯段的地壳缩短速率(约2.4mm/a)基本保持恒定;同时,晚第四纪以来砖厂段的SN向地壳缩短速率为1.43~1.81mm/a,较阿克艾肯段有明显下降,推测北轮台断裂带的SN向地壳缩短速率由西向东递减。综合对比南天山山前的逆断裂-褶皱带体系,同样反映出地壳缩短速率由西向东递减的特征。

The Beiluntai Fault is a Holocene active fault.It is the boundary between southern Tian Shan and Tarim Basin.Since the late Quaternary,steady activities of the Beiluntai fault have resulted in offsets,folds,and uplift of pluvial terraces.We used the high-resolution RTK topographic surveys to reveal that the fault scarp morphology on the Akeaiken(Ak)segment and Zhuanchang(Zc)segment of the Beiluntai fault.We found that the crustal shortening of Ak and Zc segments are dominated by thrusting and folding-uplift,respectively.We employed th optically stimulated luminescence(OSL)dating method to develop a new chronology for the different pluvial terraces,indicating that they formed at 49.14～58.51,27±3,13.72～14.64,7.13±0.88,(3.32±0.43)ka,respectively.These data permitted to estimate the crustal shortening rate(about 2.4mm/a)remains largely constant on the Ak segment,while the crustal shortening rate of Zc segment was 1.43～1.81mm/a since the Fan4 pluvial terraces was abandoned.Compared with the Ak segment,the crustal shortening rate of the Zc segment declined obviously.This shows that the NS-trending crustal shortening rate of the Beituntai fault decreased gradually from west to east.A comprehensive comparison of the reverse fault-fold belt system in the front of southern Tian Shan also indicates that the crustal shortening rate drops from west to east.