Geomorphological Characteristics And Formation Conditions Of Dongchuan Red Land In Yunnan Province

The study area is located in the southwest of Dongchuan and in the first-order structural unit of the Yangtze quasi-platform,which belongs to the secondary structural unit of the eastern Yunnan platform fold belt and the clamping zone of the Xiaojiang fault and Puduhe fault within the Sichuan-Yunnan rhombus block.Dongchuan laterite landform has various types,different shapes,various combinations and rich landscape.it is the most typical area of laterite landform development,which can be called world-class laterite geomorphology and a natural laboratory for the study of laterite geomorphology.In the field of geomorphology,the study of laterite landform is still a blank stage,and it is of great significance to study it.Based on field investigation and contour topographic map,combined with the method of visual interpretation of remote sensing images,this paper selects the world-famous laterite landform in the study area as the research object of this paper,and draws lessons from the relevant achievements of loess geomorphology.focus on the study of shallow ditches,ditches,gullies,laterite beams and their artificial landform terraces.At the same time,with the help of the relevant principles of watershed geomorphology mathematics,the geomorphological development stage of Xiaoguang River basin is studied quantitatively.At the same time,a section is selected to study the basalt and laterite in the study area.Under the guidance of the idea that everything is always the result of internal and external causes,the stratigraphic lithology,weathering,structure,neostructure,meteorology and hydrology and the conditions of human activities（farming culture）of Dongchuan laterite geomorphology are analyzed.On the basis of following the principle of laterite geomorphology classification and summarizing the previous studies on loess geomorphology,this paper draws lessons from the previous research results and experience,combined with the actual situation of the study area,on the basis of field work,the laterite landforms in Dongchuan are classified systematically.In this paper,Dongchuan laterite landform is divided into laterite gully landform,laterite gully landform,laterite gully landform and laterite artificial landform.Striated ditches,rill,shallow ditches,cut ditches,gullies,depression ditches and river ditches belong to laterite gully landforms;laterite beams and laterite slopes belong to laterite valley landforms;landslides and drains belong to laterite valley slope landforms;terraces belong to laterite artificial landforms.The elevation integral value of Xiaoguang River Basin is 0.503.In his study,Strahler believes that when the HI value is greater than or equal to 0.35 or less than0.60,the topography undulation reaches the maximum,and the geomorphology type is the most complex,which is the prime of life.According to the calculation results and the quantitative index table of the watershed development stage,the manhood of the geomorphological development of the Xiaoguang River basin can be obtained.The basalts in the study area are mainly high-potassium calc-alkaline and calc-alkaline,and the average contents of Si O₂ and Ti O₂ are 48.64%and 3.74%respectively.In Emeishan basalt,trace elements are relatively enriched,high field strength elements are relatively enriched,while K,Sr and P are relatively depleted,and their distribution curves are basically similar to those of OIB.Rare earth elements are characterized by enrichment of light rare earth elements,relative depletion of heavy rare earth elements,good fractionation of light rare earth elements and no obvious Eu and Ce anomalies.Through a large number of comparative graphic analysis,it is considered that the Emeishan basalt in the study area was formed in the intraplate environment.The laterite of HG profile in the study area has undergone a strong weathering and leaching process.Through the analysis of chemical alteration index（CIA）and A-CN-K diagrams,the laterite of HG profile in the study area has suffered strong chemical weathering under hot and humid tropical and subtropical climatic conditions,and the laterite of HG profile in the study area has reached the degree of secondary strength-rich aluminization.The formation of laterite landform is related to the stratigraphic lithology,geological structure and hydrological conditions,climatic conditions,man-made factors and other internal and external factors in the study area.It is the result of long-term synergism of internal and external dynamic geological action.