北京平原山地交界带新构造活动

NEW TECTONIC MOVEMENT IN THE TRANSITIONAL BELT OF PLAINS AND MOUNTAINS IN BEIJING

北京西山东麓和北山南麓广泛分布着山麓洪积扇地形.在按同地不同期洪积扇体平面组合关系和扇顶平面投影组合关系分类的基础上,永定河至关沟间的山麓洪积扇,其中尤其以北安河至西山农场之间的山麓洪积扇的组合类型特殊,即平面组合成串珠镶嵌型,平面投影组合成前进型.按扇顶抬升量,推算出相对抬升速度:1.3×10~4～8.4×10~3aB.P.为20.6mm/a;8.4×10~3～4.0×10~3aB.P.为1.8mm/a;4.0×10~3aB.P.以来为2.3mm/a.除1.8mm/a接近大部地区外,其余2个时期的速度均比该地区以外的地区大一个数量级,成为抬升异常区域.

The piedmont alluvial fans widespread on the east side of Xishan and the south side of Beishan. According to the plane assemblage relationship of alluvial fans which occurred in different periods at the same place and the classification of plane projection assemblage relationship of fans tops, the piedmont alluvial fans between the Yongding River and Guangou are more typical, especially the one from the Beian River to the Xishan Farm, which appear as a string of beads being inland from the view of plane assemblage and represent the advancing type through the plane projection assemblage. The rates of relative uplift estimated by the fan's top uplift are 20.6mm/a from 1.3×10~4 aB.P. to 8.4×10~3 aB.P., 1.8 mm/a from 8.4×10~3 aB. P. to 4.0×10~3aB.P., and 2.3 mm/a since 4.0×10~3 aB. P.. Apart from the rate of 1.8 mm/a, the others are quicker than that of adjacent places, indicating that this region is unusually uplifting area.