北天山安集海河大峡谷3.7 ka以来的快速下切  

Rapid incision events since 3.7 ka in the Anjihaihe Gorge along the northern Tianshan range, China

作　　者：胡贵明 陈杰[2] 覃金堂[2] 李盛华[1,2] Guiming Hu;Jie Chen;Jintang Qin;Sheng-Hua Li(Department of Earth Sciences,the University of Hong Kong,Hong Kong,China;State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China)

机构地区：[1]香港大学地球科学系,香港 [2]中国地震局地质研究所,地震动力学国家重点实验室,北京100029

出　　处：《科学通报》2020年第15期1506-1518,共13页Chinese Science Bulletin

基　　金：中国香港特别行政区研究资助局基金(17303014,17307117);中国地震局地质研究所基本科研业务专项(IGCEA1810);地震动力学国家重点实验室课题(LED2016A05)资助。

摘　　要：北天山前陆冲断带的河流阶地记录了河流在构造和气候的共同作用下所发生的加积和侵蚀过程.其中,安集海河大峡谷至少发育了18级基座阶地.应用改进的光释光测年方法,对阶地上覆黄土及阶地砾石堆积中粉砂透镜体进行了年龄测定.结果表明,安集海河3.7 ka至今的下切深度为260 m,最大平均下切速率7 cm/a. 3.7 ka以前,峡谷加积了巨厚的灰黑色砾石层(厚度大于200 m);3.7 ka以后河流逐级下切砾石层,发育了13级基座阶地. 3.0~2.4 ka的600年间安集海河加速下切,平均速率达15 cm/a. 1.3 ka时,河流下切至第四纪以前形成的基岩层,至今形成了5级基岩基座阶地.安集海河大峡谷18级阶地是气候变化、河流水/沙平衡关系等影响的结果.Young river terrace levels distributed along active tectonic regions and major river channels record the histories of the most recent tectonic activities and geomorphological evolution. There are 18 terraces in the upper reach of the Anjihaihe River,along active zones of the northern Tianshan in China. The surface of these young terrace insets is covered by Aeolian loess and fluvial deposits. Consequently, optically stimulated luminescence(OSL) dating was used to reveal the burial ages of those sediments, and to calculate the tectonic deformation and fluvial incision rate. However, the ages of young quartz sediments are difficult to determine due to the weak and dim OSL signal characteristics, and therefore geological and geomorphological information was not forthcoming. Recently, however, a "simplified procedures" methodology was developed to overcome these dating problems.Loess deposits can constrain the minimum abandonment age and fluvial sands were used to provide the age limits of formation, which correspond to the maximum and minimum incision rates. The elevation of each terrace above the modern river bed was obtained using a Digital Elevation Map with 12-m resolution, Google Earth images, and portable Global Positioning System measurements. Together with the results of the OSL dating and the elevation measurements, we conclude that the Anjihaihe River has incised the gorge to a depth of ~260 m since 3.7±0.2 ka, with a maximum average incision rate of 7.2±0.1 cm/a. The incision record can be divided into four major stages: ~3.7-3.0, ~3.0-2.4, ~2.4-1.3 ka,and from 1.3 ka to the present;the respective average incisive rates are 3.1±0.3, 15±0.3, 8.5±0.2, and 4.6±0.4 cm/a. The results indicate that the incision occurred in a series of steps which coincided with environmental changes in the region. As a result, this set of 18 strath terrace levels has recorded the aggradational-degradational surface processes of the Anjihaihe River gorge since ~3.7 ka. Before ~3.7 ka, a thickness of ~260 m of fluvial sands

关 键 词：天山北麓 安集海河大峡谷 年轻阶地 光释光测年 加积-侵蚀过程 

分 类 号：P931.1[天文地球—自然地理学] P597