天山北缘河流阶地形成及构造变形定量分析

新生代以来,北天山山前发育了3排冲断褶皱带。新生代晚期一系列河流普遍穿过这3排冲断褶皱带并发育了三级河流阶地。在最新构造活动的影响下,河流阶地普遍发生变形,遭受抬升。利用光释光及14C年代学方法确定了塔西河三级阶地的形成年龄,并实际测量了三级阶地的高程。结果表明吐谷鲁背斜的构造抬升速率在32．85-28．75 ka问为9．50-12．57 mm／a,12-13 ka间为9．67-14．5 mm／a,全新世则增至10．79-23．44mm／a,天山基底的平均隆升速率达到3．39-3．86mm／a。通过对天山最高一级夷平面、野外实测侏罗纪地层高程及天山发育的煤层的相对隆升速率的研究则表明天山自24 Ma以来平均的隆升速率约为0．085-0．146 mm／a。结合对北天山其他主要河流阶地的观察及研究可以看出自晚更新世一全新世以来,天山北缘的最新构造活动具有不断加快的特征。

The Late Cenozoic Deformation of Terraces on the North Flank of Tianshan Mt. and the Tectonic Evolution

Stream terraces are developed in several rivers since the late Cenozoic, cutting across three rows of thrust-fold belts along the north flank of the Tianshan Mt. in the NW China. These terraces have been mostly folded and uplifted since the active tectonics in late Cenozoic. Based on the measurement of the heights and the OSL age dating of the deformed terraces in Taxi river, the authors estimate that the uplifting rates of Tugulu anticline are about 9.50-12. 57 mm/a during 32. 85~28. 75 ka, 9. 67- 14. 5 mm/a during 12-13 ka and 10. 79 -23.44 mm/a in the Holocene, respectively, while the average uplifting rate of the Tianshan Mt. is about 3.39 ~3.86 mm/a. However, studies on the height of planation surface, Jurassic strata and coal strata show that the average uplifting rate of the Tianshan Mt. is about 0.085-0.146 mm/a since 24 Ma. All these data combining the observation on terraces of other rivers show that the tectonic uplifting rate of the northern Tianshan Mt. is acceletating.