KMS Institute of Mountain Hazards and Environment,CAS
|Alternative Title||STUDIES ON NEOTECTONICS IN DALI-LIJIANG REGION|
|陈富斌1; 赵永涛1; 徐毅峰2|
大理-丽江地区处在横断山系的核心部位，区内的玉尤雪山(海拔5596 米)、苍山(海拔4122 米）是云南西北部的主要山峰。这一地区在大地构造上位于西南地台向西凸出部的边缘与秦川印支褶皱带、滇藏燕山褶皱带的接合部，构造十分复杂；在大区域地貌上属于强烈侵蚀切割的褶皱断块平行高山与宽谷(盆地)区，山地的层状地貌发育，第四纪盆地的堆积深厚，活动断裂的规模很大，是新构造强活动区，“万里长江第一弯”的金沙江大迥折与地球大陆上切割最深的峡谷(虎跳峡)就发生在这里。20 世纪初叶以来，国内外地学工作者进行过多次考察，积累了大量资料。就横断山系而言，这里的地学调查程度是比较高的。然而在众多的地学文献中，晚新生代地质系统研究文献很少。在50 年代后期和60 年代，这里的新构造现象已由一些学者所注意，从地貌学的角度作过分析。70 年代后期以来，随着地震地质工作的加强，新构造研究得到更多的却注意，直接涉及新构造的文献亦增多，不过区域新构造专论仍然缺乏。该地区处于青藏高原东南缘地质灾害带上，又是云南西部的重要经济文化发展区，加强作为地质灾害预测预报的地质基础的新构造研究，在理论与实践上都是必要的。本文是笔者等在前人工作的基础上，于1979 年与1986 年新构造专题考察也所积累的资料的总结，作为这方面的补充，提供参考。
Mt. Yulongxue (5596 meters a. s. l. )and Mt. Cangshan (4122 meters a. s. l. )which are located in the southeast of Tibet Plateau and the centre part of the Hengduan Mountain System are major peaks in the northwest part of Yunnan province. 1n this region , the geomorphic type belongs to paralled fold-fault high mountains and basins of the intense erosion and deep down-cutting; the stepped landforms are developed in the mountain land; the Quaternary sediments are 2000 meters in the basin and active faults are long. This is an intensive mobility region of the neotectonics. That is why there are the great turn of the Jinsha River and the Hutiao Canyon appearing this region.
By the neotectonic analysis of the Quaternary superposition and hiatuses in the basins, the horizon of the residuum of laterite type under the lower stratum in the basins , the information of paleoplanation in mountain land and the terraces of rivers and lakes. the conclusions of this text are as follows:
The major basins in the region are graben ones duringthe neotectonic period. The Songmaopo Formation in the lower part of the basins is unconformably overlying on the Precenozoic. The residuum of laterite type was developed along the unconformity. 1t is buried palaeoplanation surface. AII these show that the landform in the region is developed with the differential block movement , namely neotectonic movement ,on the extensive uplifting background. The regional unconformity represented by the residuum of laterite type under the Songmaopo Formation is the neotectonic mark of the lower Iimit. The lower boundary of neotectonic period is 3.3 million years BP. or so . In other areas of the Hengduan Mountain System , they are 3.16-3.4 million years BP. in Kunming.3.4 million years BP. in Yuanmou and 3.3 million years BP. in Panzhihua. The boundary is close to Gauss/Gilbert in the paleomagnetic chronological scale of Late Cenozoic.
The facts that the five unconformities occurred in the Quaternary Column , which hap pened 3.3 million years BP. or so. between the end of Early Pleistocene and the beginning of Middle Pleistocene. between the end of Middle Pleistocene and the beginning of Late Pleis tocene. 34-30 thou. years BP. or so and 8-7 thou. years BP. or. so ,show that the neotectonic f1uctuation has the progression and its trends are to shorten the cycle of f1uctuation. to increase the frequency and to strengthen the differential block movements in Late Quaternary.
During the neotectonic period, the uplifiting quantities has accumulated to 2200-4400 meters; the gradient of differential block movenment has accumulated to 4000 meters; the average rate is 0.4-0.6 mm/y for the accumulation in the basins and the value for accumulation in the basins and the value for accumulation in the basin with uplifting in the mountain land is 0.3-0.6/l.
The landform forming process in this region has experienced three stages, namely peneplana tion stage (previously 3.3 million years BP. ) and lake-basin stage in the mountain land (from 3.3 million years BP. to the end of Early pleistocene) and river stage in high mountain (since Middle Pleistocene). The last two stages belong to the neotectonic period. The neotectonic movement has controlled the important transform of landform forming process , the pattern of regional landform and the forming of neotectonic landform. The great turn of the Jinsha River and the deep down-cutting of the Hutiao Canyon closely connected with the turn are a special phenomenon of neotectonic landform. Obviously , the neotectonics is the major factor for the landform forming of the young orogenic zone.
|陈富斌,赵永涛,徐毅峰. 大理-丽江地区新构造研究. 横断山系新构造研究. 成都:成都地图出版社,1992:64-80.|
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