Research On Geomorphic Features In Wandian, Mengtong And Fengqing Of Western Yunnan Province

With the rising popularity of 3S technology in the field of research on landscape, quantitative research on landscape has become increasingly mature. It is widely acknowledged that the study of geological background and metallogenic prospect of a region through the earth’s surface can provide a scientific basis for these activities related to human life, like the exploitation of mineral resources, engineering construction, geological disaster assessment and control, environmental protection, tourism development, etc.Based on the Geographic Information System(Arcgis), a research on topographical features of western and southern region of Fengqing of the Lincang city in Yunnan Province is done, by analyzing and processing the digital elevation data(DEM), remote sensing data(Landsat8 OLI-TIRS), the related geological data and the field investigation. The geologic origin of the study area is summarized and the specific results obtained from this research are as follows:(1)By using the basic landscape classification index of Bing-yuan Li(2008) and based on the special topographical condition in the study area(absolute altitude:579-3044 m, relief degree:0-714 m), the study area is divided into 13 kinds of basic geomorphic types, low-altitude plain, low-altitude platform, intermediate-altitude platform, sub-high altitude platform, low-altitude hill, intermediate-altitude hill, sub-high altitude hill, low-altitude and low-relief mountain, intermediate-altitude and low-relief mountain, sub-high and low-relief mountain, low-altitude and intermediate-relief mountain, intermediate-altitude and intermediate-relief mountain, sub-high and intermediate-relief mountain.The landform’s morphological characteristics in the study area are as follows:on the altitude, low in west but high in east; on relief, Wandian is the largest, the larger relief in Mengtong often exists in north-south mountains, the larger relief in Fengqing often exists in northwest-southeast mountains.The combination of landform of the study area is mainly divided into three types: intermediate or sub-high altitude mountain of tectonic denudation, intermediate or sub-high altitude mountain of erosion-denudation and piedmont plain-platform. The landform in Wandian is represented by canyon and well-developed river terrace. The landform in Mengtong is represented by very well-developed wide valley and widely distributed erosion-sediment valley. The landform in Fengqing is represented by the northwest-southeast line of piedmont plain and the intermediate altitude mountain of tectonic-denudation.The manifestation of drainage network distribution on the study area is that the main stream stretches are north-south or northwest-southeast. The mainstream of Wandian area is Kejie River-Wandian River, the branch streams of Wandian area are Yaoguan River and Ganzheba ravine etc, mainly stretching north-south. The drainage network of Mengtong area is mainly made up of five mainstreams and other branch streams.Mainstreams stretch north-south and branch streams stretch northwest-southeast or northeast-southwest. The mainstreams of Fengqing area are Fengqing River and Mengyou River, the branch streams are mainly ravines, whose stretchs are always northeast-southwest.(2)Typical landform of the study area is divided into five genetic types, which comprise tectonic-landform, fluvial landform, gravitational landform, karst landform and man-made landform.Tectonic-landform comprises Wandian Basin, Mengtong Basin, Fengqing Basin, Parallel ridges landform in Fengqing, canyon landform etc.Fluvial landform comprises ravine-landform, diluvial fan, river terrace, erosion-landform, meander core etc. Gravitational landform comprises collapse and landslide landform, Karst landform comprises cliff and karst landform, man-made landform comprises overlook landform of Fengqing.(3)The drainage network development of the study area has been directly controlled by Kejie fault so far. By Xianyi-Zhang(2005). the property of Kejie fault transformed into overthrust in Mesozoic-Cenozoic. West hanging wall has been lifted by overthrust and the west caprock of Wandian area has been lifted since then that canyon is well developed in southwest of Wandian. The drainage network in northwest is controlled by Daqiao fault and that in northeast or southeast is controlled by Changning-Yingpan fault. The well-developed hotsprings in Xiqian. Yangliushu-gou, west Yanzi-bian reflect the overthrust property of Changning-Yingpan fault. The northwest-southeast stretch of Mengyou River, especially that of Fengqing River, reflects property of dextral strike-slip of Lancang river Orogenic Belt. The Lancang rock group and Lincang granite pluton have been lifted by the overthrust of Tianxin fault that this area turns into the highest area in the study area. Many ravines with northeast-southwest stretch distribute on both sides of the highest area by the Exogenic Process.There has been an accelerated movement in the study area since the late Pliocene especially Quaternary, in the background of tilted type lifting in western Yunnan Plateau. Wandian Basin had been controlled by Kejie fault. The earth’s crust has dropped in graben form. The area near Mengtong Basin was raised by overthrust nappe, at the same time, forced by continuous planation from the tributaries of Nu River and Lancang River, the altitude there declines, but is much higher than Wandian Basin; There is a great amount of crustal uplift in Fengqing area, which has been affected by Lancang River Orogenic Belt since Quaternary period, thus evolving into the highest area in study area. To sum up, the study area has evolved into the intermediate and sub-high altitude and high in east but low in west landform under comprehensive influence of the regional tectonic framework and outer dynamic geological process with keeping the Pliocene planation surface(Account for 94.66%).