祁连山东段童子坝河阶地对气候变化与新构造运动的响应*

通过对祁连山东段童子坝河各级阶地的年代和变形程度进行测定,得到了河流阶地的形成年代和过程,推算出民乐—大马营逆断裂的活动强度和速率,并分析了阶地形成和气候变化之间的关系。童子坝河5级阶地(年龄分别为16.70±1.81 cal,ka BP、 10 092.5±27.5 cal a BP、8127.5±72.5 cal a BP、2900±60 cal a BP、282.5±17.5 cal a BP)均形成于气候由冷转暖的阶段,属于气候成因阶地。基于断裂两侧阶地面的平面几何形态并结合上、下盘阶地横剖面同级阶地的高差,得到T4、T3、T2和T1阶地在民乐—大马营断裂处的垂直位错分别为10.6±3.1,m、5.0±2.6 m、2.0±1.9 m和1.9±1.3 m,推算出全新世以来民乐—大马营断裂的垂直滑动速率为1.05±0.31 mm/a,水平缩短速率为1.02±0.60 mm/a。

Terraces of the Tongziba River,eastern Qilian Mountain and their responses to neotectonic movement and climate change

Based on fluvial terraces dating and deformation determination,the formation age and processes of river terraces of the Tongziba River,eastern Qilian Mountain are obtained. The activity intensity and rate of the Minle-Damaying thrusting fault are calculated and the relationship between the formation of terraces and climate change is analyzed. Dating results in comparison with climate curves or events indicate the five fluvial terraces with ages of 16.70±1.81cal ka BP,10 092.5±27.5 cal a BP,8127.5±72.5 cal a BP,2900±60 cal a BP and 282.5±17.5 cal a BP,formed during the transition from warm to cold climate. Based on the plane geometry of fluvial terraces on both sides of the Minle-Damaying fault as well as height differences between the same level terraces located in hanging wall and footwall,vertical offsets of T4-T1 were estimated to be 10.6±3.1 m,5.0±2.6 m,2.0±1.9 m and 1.9±1.3 m,respectively. By integrating the various research results,it is concluded that the vertical slip rate of the Minle-Damaying fault was 1.05±0.31 mm/a and horizontal shortening rate 1.02±0.60 mm/a since the Holocene.