Late Quaternary Strike-slip Characteristics And Basin Evolution Of The Menglian Fault In Southwestern Yunnan

In this paper,we study the geometric and segmental features of the Menglian fault in the NE-NEE direction,the characteristics of the Late Quaternary and the role of faults in the evolution of the basin.Combining the research results of predecessors,the following conclusions are obtained:(1)The Menglian fault is a left-lateral strike-slip fault in southwestern Yunnan,of which the trend is NE-NEE.The eastern part of the fault runs toward NE,and the middle and west sections go to trend of NEE.According to the discontinuity and branching characteristics of the fault trace,the fault is divided into three parts and four sections,which are the eastern section(LancangNaxiao section),the middle section(Naxiao-Paliang section),the western section(Paliang-Mengma section)and the southern section(DongmuMeiguoguang section).The eastern section begins at the southern margin of the Lancang Basin and extends to the southern margin of the Mengbin Basin,which extends for about 18 km.Due to the close proximity of the Hanmuba-Lancang fault of right-lateral strike-slip characteristic,the shape of the section is curved;the middle section of the west of the village is to the SWW via Langley and Menglian to Paliang,with fault scraps of unequal height and deep fault valleys,which extends for about 39 km.(2)The strike-slip faulty geomorphology along the Menglian fault is relatively developed,forming multi-level left-lateral dislocation rivers,gully and terrace,and the observed minimum left-lateral dislocation is about 7 m.Using the high-precision LiDAR measurement method and using the Luminescence dating method(OSL),four typical horizontal dislocation geomorphologies were finely measured.According to the corresponding geomorphological age obtained,the average left-lateral rotation since the Quaternary fault was obtained.The slip rate is 2.2 ± 0.4 mm/a.The results are equivalent to the sliding speed of other NE-to-left-lateral strike-slip faults in southwestern Yunnan,reflecting the overall coordination of regional tectonic activities.According to the maximum left-handed dislocations of cross-fault geologic bodies of 9.5±1.8 km,the age of the left-lateral strike-slip is estimated to be about 4.7±1.6 Ma,which is the middle and late Miocene.(3)Based on existing research conclusions,a new understanding is proposed based on the active fault and the investigation of the Quaternary basin along the fault.Through satellite image interpretation and Geological Survey,it is believed that the faults control the development of three Late Cenozoic basins along the unilateral or intermediate areas of Mengbin,Menglian and Mengma.The three basins are not typical pull-apart basins.After the interpretation of the geomorphology of the Mengbin basin along the fault and the profile analysis and geological survey of the mining plant,the initial activity time of the fault was determined to be from the late Miocene,and the area of slip rate estimation is consistent.Combined with the distribution pattern and characteristics of the geomorphology,the general shape of the Mengbin Basin is controlled by the early NW fault and the Menglian fault and is controlled by the Nanla River and its tributaries in the later period.The geomorphology and geological characteristics of the Menglian and Mengma basins are analyzed.It is believed that the Menglian Basin is formed by the combination of continuous strike and slip and river erosion.The early channel of the Mengma Basin was abandoned by the influence of left-lateral strike-slip,and the three tributaries Erosion forms the shape of today's diamonds.