巧家盆地第四纪洪积物沉积阶段及其对小江断裂带北段活动性的指示

Quaternary activity in the northern section of the Xiaojiang fault zone

通过对巧家盆地第四纪洪积物沉积阶段及其沉积年代进行分析,为小江断裂带北段第四纪活动性研究提供沉积学证据。研究结果表明:巧家盆地形成于早更新世中期,平均断陷速率为0.59 m/ka,共发育了5个洪积相沉积层。第四纪以来小江断裂带北段处于构造平静期与活跃期相互交替的阶段,期间共经历了早更新世中期~1.6 Ma,0.81~0.79 Ma,0.65~0.59 Ma,0.48~0.4 Ma,0.12 Ma至今等5期构造活跃期,其中0.48~0.4 Ma和0.12 Ma至今为小江断裂带北段构造活动最强烈的阶段。小江断裂带北段活动性与新构造运动过程有着密切的成因联系,受控于青藏高原东南缘持续的侧向扩展挤出作用,但相较于断裂带中段活动性偏弱。

In this study,we analyze sedimentary stages in the Quaternary diluvium and its time of deposition in the Qiaojia Basin to provide sedimentological evidence of Quaternary activity in the northern section of the Xiaojiang fault zone.The results show that the Qiaojia Basin was formed in the middle of the early Pleistocene,with an average rift rate of 0.59 m/ka,and this led to the development of five diluvial sedimentary layers.Since the Quaternary,the northern section of the Xiaojiang fault zone has undergone alternating stages of quiet and active periods of tectonic activity.Five periods of tectonic activity have occurred:From the middle of the early Pleistocene to 1.6 Ma,0.81 to 0.79 Ma,0.65 to 0.59 Ma,0.48 to 0.4 Ma,and 0.12 Ma to the present.The period from 0.48 to 0.4 Ma and 0.12 Ma featured the most intense stages of tectonic activity in the northern section of the Xiaojiang fault zone.Activity in this section was closely related to the process of neotectonics,which was controlled in turn by continual lateral expansion and extrusion on the southeast edge of the Qinghai Tibet Plateau.However,this activity was weaker than that in the middle section of the fault zone.