金沙江龙蟠断陷谷地与河床覆盖层的成因初探

通过河床钻孔并结合野外踏勘,确定了隐伏的龙蟠断裂在宽谷的切错位置,指出古龙蟠谷地是在上新世末早更新世初由龙蟠断裂发生逆断走滑和白汉场断裂的正断左旋并伴随断块的垂直升降活动而形成。河床覆盖层由现代金沙江冲积层和下伏的一套古湖相堆积物组成,其中古湖相堆积具有明显的分层性,由底往上可划分为冰缘冻融泥流堆积物、含泥质的灰绿色细砂和黄褐色粉土层、崩坡积和冲洪积加积物、灰绿色淤泥质碎石土层,结合区域性地质环境演化背景,认为它们是受中更新世时期本区间歇性山体抬升和冰川活动等新构造运动影响的不同沉积环境下的产物,从而清晰地揭示了河床深厚覆盖层的成因,为认识金沙江宽谷河段发育史提供了极其重要的信息。

A PRELIMINARY STUDY ON THE FORMATION OF LONGPAN RAMP VALLEY AND RIVERBED DEPOSITS IN JINSHA RIVER

With the information disclosed by the riverbed bores and field investigation,the exact place of covered Longpan fault was identified in the adolescent valley of Jinsha River.Then the formation mechanism of the old Longpan ramp valley was figured out.In fact,Longpan fault was a reverse slip fault and the Baihanchang fault was a normal left-rotation fault.Due to the different vertical motions of the zones of fracture,the old ramp valley came into being.In the evolutionary period,thick deposits developed in the valley.Through the drill cores,an important phenomenon was revealed that the deposits had a well-regulated layered fabric and multi-type components.The regional geology shows that the layered deposits was a result of different sedimentary environments and the disparate components accorded very well with the corresponding new tectonic movements such as periodic mountain raising and glaciations in middle Pleistocene in this region.