四川雀儿山错坝断裂活动特征

Activity characteristics of the Cuoba fault in Queershan,Sichuan province

错坝断裂走向NW50°、长约26km、展布在川藏交界海拔4000m以上高山,属于甘孜-玉树断裂带的一条分支断裂。研究错坝断裂活动特征有助于了解甘孜-玉树断裂带东南段南西侧分支断裂的活动性。错坝断裂的断错地貌现象丰富,有基岩断崖、断层沟、坡中谷、冲沟水平扭曲。这些现象分布在拔河高度上百米的山体。实测17个地层热释光测年样品,其中7个样品断错了距今18~51ka地层,其余10个样品为地貌面地层年代样品。结合地层测年及地貌面分析,厘定错坝断裂的最新活动时代为距今18~16ka之间,属于晚更新世晚期活动断裂。错坝断裂晚更新世晚期的左旋走滑活动速率约为1.4mm/a,垂直活动速率约为0.3~0.7mm/a。该断裂在晚更新世时期至少有过3次活动。

Cuoba fault is about 26km long with a strike of NW50°,and crosses the high mountains above altitudes 4000 meters in the boundary between Sichuan and Tibet.It belongs to a branch fracture of Ganzi-Yushu fault zone.Study on activity characteristics of Cuoba fault can help to understand the activity of the branch fracture which is located in the southwest side of the southeastern segment of Ganzi-Yushu fault zone.Dislocated landform phenomena of Cuoba fault are abundant,such as bedrock scarps,fault groove,valley in slope and horizontal contortion of gullies,etc.These phenomena are distributed among the mountains hundreds of meters above river level.The 7 out of 17 strata TL dating samples represent the age of the dislocated strata,which is about 18~51ka BP.The rest 10 samples are the dating samples of the morphologic surfaces layer.Combining strata dating and the analysis of the morphologic surfaces,the latest activity time of Cuoba fault is 18~16ka BP,and it is an active fault with sinistral strike-slip rate of about 1.4mm/a and vertical activity rate of about 0.3~0.7mm/a in later period of late Pleistocene.Cuoba fault had at least three events in the late Pleistocene period.