维西-乔后断裂新活动特征及其与红河断裂的关系

根据野外调查结果,重点阐述了维西—乔后断裂晚第四纪活动特征,并对其与红河断裂之间的关系进行了探讨分析。维西—乔后断裂对晚新生代盆地具有明显的控制作用,右旋走滑特征明显,沿线山脊和河流表现为同步右旋位错。德胜和长邑南探槽揭示其断错了晚更新世晚期—全新世堆积。岩曲—石岩村一带Ⅱ级河流阶地和后缘洪积扇上发育长约3 km、高2.5 m左右的断层陡坎。根据洪积扇、冲沟和河流阶地位错量估算,该断裂晚更新世晚期以来右旋水平滑动速率为1.8~2.4 mm/a,垂直滑动速率为0.30~0.35 mm/a。它南与红河断裂相连,北与金沙江断裂相接,新生代以来具有与红河断裂和金沙江断裂相似的运动学特征、相同的地质演化历史和构造变形机制,是红河活动断裂的北延部分。维西—乔后断裂与红河、金沙江以及德钦—中甸—大具等断裂一起,共同构成了川滇活动块体的西部边界。

RECENT ACTIVE FEATURES OF WEIXI-QIAOHOU FAULT AND ITS RELATIONSHIP WITH THE HONGHE FAULT

According to geological and geomorphic field observations, in this paper, we mainly elaborate the late Quaternary active features of the Weixi-Qiaohou fault, and discuss its relationship with the Honghe fault. The fault have apparently dominated many late Cenozoic basins'' development, showing dextral strike slip motion features as being documented by synchronous right-lateral dislocation of mountain ridges and rivers along it. It has displaced late Pleistocene to Holocene accumulations revealed by the exploratory trenches at Desheng and the site south of Changyi. Nearby Yanqu and Shiyan, there is a 3 km long, ~2.5 m high fault scarp on the river terraces and the alluvial fans. It is estimated the fault has a average rate of 1.8~2.4 mm/yr. horizontally and 0.3~0.35 mm/yr. vertically since late Pleistocene, based on displaced magnitude of the alluvial fans, gullies and river terraces. It is a significant link which connects with the Honghe fault in the south and with the Jingshajiang fault in the north. Since late Cenozoic, the Weixi-Qiaohou fault in kinematics is similar to the Honghe fault and the Jinshajiang fault, they having identical geological evolutionary history and tectonic deformation mechanism, accordingly,indicating that the Weixi-Qiaohou fault should be the northern segment of the Honghe fault. The Weixi-Qiaohou, Honghe, Jinshajiang as well as Deqin-Zhongdian fault composed of the western boundary of Sichuan-Yunnan active block all together.