滇西北丽江-大理地区第四纪断裂活动的方式、机制及其对环境的影响

滇西北地区早更新世时全面隆起,中更新世发生陆内裂谷作用,云南高原面解体,晚更新世是地堑系发育的全盛时期,全新世这一过程仍在进行。断块的差异隆升运动造成该区自北、西向南、东呈台阶状降低,形成了玉龙山等断块山。断裂活动控制了盆地、河流、湖泊、冰川、温泉及其沉积。青藏高原隆升产生向南偏东的推挤使川西-云南的断裂活动具相同的方式,断陷盆地发育主要受近南北向左行剪切-拉张活动控制。

THE MODES AND MECHANISM OF QUATERNARY FAULT MOVEMENT IN LIJIANG-DALI AREA, NORTHWESTERN YUNNAN AND THEIR INFLUENCE ON ENVIRONMENT

The Quaternary tectonic framework of Lijiang-Dali area, Northwestern Yunnan, could be regarded as a graben system, which is composed, from west to east, of the Qingshuilang Mt., the Madeng-Qiaohou-Weishan Basins, the Yunling and the Diancang Mrs., the Jianchuan-Eryuan-Dali-Midu Basins, the Yulong Mt., the Lijiang-Heqing-Songgui Basins, the Jinshajiang Rise, and the Jinguan-Yongsheng-Qina-Binchuan Basins. The development of fault-depressional basins should be controlled by the Weixi-Qiaohou, the Jianchuan-Erhai, the East of Yulong Mt. and the Chenghai Fracture (Zone) respectively. Namely, the nearly S-N fractures in the area seem to be transtensile during Quaternary. The Yunnan Plateau Plane, a planation surface formed in the mid-late period of Pliocene, has been uplifted more than 2 200m. The vertical separation could be up to 1 230m since the Mid Pleistocene, and about 30—70m during Holocene. The neotectonic features of the area could be well comparative with that in the Qinghai- Xizang (Tibet) Plateau. The activities of its boundary fractures reveal that the plateau has been uplifting and overthrusting since Early Pleistocene. The uplifting of the area in the Early Pleistocene should be related with the plateau. The overthrusting outwards of the plateau might result in a SSE-NNW compressive stress field. Three neotectonic units could be distinguished: the Central-Eastern Yunnan Graben System caused by the rejuvenated S-N fractures, the Baicaoling Rise in the Central Yunnan, and the Northwestern Yunnan Graben System. The latter was once situated in the margin of the Yangtze Block, the S-N fractures, as well the NE-SW and W-E fractures, rejuvenated. Furthermore, a local S-N compressive stress field, resulted from the resistance of the Wuliang Mt., might give rise to the formation of NNE (sinistral) and NNW (dextral) conjugate fractures, which might play a role in the formation of the graben system. Owing to the inhomogeneous uplifting and sinking, the disintegrated Yunnan Plateau Plane, the basins, the ice-scour lakes, the glaciated terraces, etc., are distributed in several elevations. Southwards as well eastwards, the step-by-step descendence of them could be observed. The faultblock mountains, such as the Yulong and the Diancang Mts., formed jus.t in the districts of stress concentration. The rivers, lakes, glaciers and springs, also their deposits, might be controlled principally by the fractures. The rich resources, such as peat, geothermal field, mineral spring and tour geology, reserved in the graben system, should be evaluated scientifically and exploited rationally.