滇西北永胜地区主要活动断裂与活动构造体系

THE MAIN ACTIVE FAULTS AND TECTONIC SYSTEM IN YONGSHENG AREA,NORTHWESTERN YUNNAN

位于滇西北断陷带东北部、程海—宾川断裂带北端的永胜地区上新世以来断裂活动强烈,构造地貌特征显著。永胜地区1∶50000活动构造填图发现,区内共存在各类断裂14条。其中金官断裂（F1）、永胜断裂（F2）、木耳坪羊坪断裂（F3）三者规模最大,活动性亦远超其他断裂,属于程海—宾川断裂带的一级分支断裂,其他断裂为程海—宾川断裂的二级分支断裂。构造地貌特征、错断地质体及擦痕统计等均指示区内断裂现今主要以伸展正断活动为主,根据活动性的差异可将其分为强、较强、中等、弱、极弱5类,其中金官断裂的活动性最强,垂向活动速率可达0.20-0.26 mm/a。对永胜地区主要断裂几何学、运动学特征的研究及动力学机制的讨论可知,永胜地区主要断裂在平面上构成向东突出的弧形旋扭构造体系,在剖面上表现为张扭性断裂常见的负花状构造;程海—宾川断裂带现今活动主要是在近南北向主压应力作用下产生的近东西向的伸展正断,并因为叠加了旋扭作用而具有一定左旋走滑。永胜地区的弧形旋扭构造体系及滇西北断陷带等均是在川滇内弧带顺时针旋转及南汀河断裂、畹町断裂与理塘断裂的走滑拉分共同作用下形成的。

Yongsheng located in the northeast of Dali fault system and the north end of ChenghaiBinchuan fault zone. Faults in Yongsheng area have been strongly active since the Pliocene and with significantly tectonic geomorphology characteristics. According from 1： 50000 active fault mapping,there are 14 faults in Yongcheng-Jinguan area. Jinguan Fault（ F1）,Yongsheng Fault（ F2） and Muerping-Yangping Fault（ F3） are the largest scale and with strongest activity among them. They belong to the first class branch faults of Chenghai-Binchuan fault zone,the others belong to the second class branch faults. Tectonic landform characteristic,geological bodies broken by fault and the results of striations statistics all indicate that faults in Yongsheng area normal fault activities was the predominance. According to the activity,faults in this area are divided in to five classes,including stronger,strong,medium,weak and weaker. Jinguan fault is the most active fault among them,the vertical movement rate up to 0. 2 - 0. 26 mm / a. The geometry,kinematics and dynamics features of the main faults in Yongsheng area have been discussed. The result shows that the faults in Yongsheng area make up an east protruding curved rotational shear tectonic system in the plane,and form a negative flower structure in profile which was very common among transtension fault system. The current activity of Chenghai-Binchuan fault zone is near EW extension is mainly caused by the near SN compressive stress. And it has a certain left lateral strike slip because of the superposition of the twisting action. The curved rotational shear tectonic system in Yongsheng area and the Northwest Yunnan rift zone are all form from arc belt clockwise in Sichuan-Yunnan and the strike slip puil apart process of Nandinghe fracture、Wanding fracture and Litang fracture.