滇西北周城—清水断裂带晚新生代活动性初步研究

地表地质调查发现,位于滇西北菱形断块中南部的周城—清水断裂在上新世早期已经开始活动,而断裂强烈活动时期在中更新世,晚更新世以来活动性减弱。断裂运动方式以左旋走滑为主,兼有逆冲分量,并发生过从逆冲到正断的转换,全新世活动不明显。根据断裂断错的上新世昔格达组湖相沉积地质及河流地貌进行的初步分析,可以判断该断裂晚第四纪以来的垂直活动速率为0.1 mm/a左右,明显小于周城—清水断裂北侧川滇菱形块体向南东方向的运动速度(13~14 mm/a)。这表明周城—清水断裂对印度板块与欧亚板块碰撞所形成的次生构造———川滇菱形块体的侧向挤出的调节作用很有限。

The Late Cenozoic Activity of the Zhoucheng-Qingshui Fault Zone in Northwest Yunnan Region

The northward convergence of India into Asia over the past 50 m.y.has led to the development and lateral extrusion of thickened crust.On the basis of velocity field constrained by GPS measurements,the Chuandian active crustal block adjusts the crustal lateral extrusion movement by clockwise rotation on a background of southeastward movement.The block exhibits a relatively homogenous movement at rates 19 mm/a and decreases to be 13-14 mm/a across the NE-striking faults such as Lijiang fault.The fact suggests that NE-striking faults have prevented the movement of active crustal block.Field observations collected recently show that the Zhoucheng-Qingshui fault zone,located in the interior of the Chuandian active crustal block,is an important component of the active tectonics.The fact that the early fault trace well preserved in riverine-lacustrine deposit and covered by the Xigeda Group deposited during the Pliocene suggests that the faulting onset in Early Pliocene.Many phenomena indicate the Zhoucheng-Qingshui fault zone is characterized by sinistral strike-slip faults with the component of normal or thrust along the fault zone striking NE45°during Quaternary.Age results of Thermoluminescence(TL) and Electronic Spin Resonance(ESR) indicate that the fault zone reactive during Mid-Pleistocene,and its activity has become weak since Late Pleistocene.The fault prevented southeastward movement of active crustal block.A long-term slip-rate of 0.1 mm/a of deformation on this fault,derived from the cumulative offset and Pliocene lacustrine deposit,is much slower than that of the Chuandian active crustal block,which suggests that the Zhoucheng-Qingshui fault zone isn't a significant factor in accommodating of the continued southward movement of the active crustal block.