Research Of Quaternary Strata And Active Fault In Lianghe And Yingjiang Basin Of Dayingjiang Valley, Southwest Yunnan

Dayingjiang valley, locating in the southwest of Yunnan Province and thesoutheast corner of Himalayan tectonic belt, is the key area for the neotectonicresearch of Yunnan-Guizhou plateau. Lianghe basin and Yingjiang basin, locating atthe Dayingjiang valley, is the ideal area for the research of Quaternary sedimentation,morphogenesis, neotectonic and active tectonic, for the thick Quaternary strata,variety geomorphic types, strong active tectonic and multiple violent earthquake. But,there is little research work about Quaternary for this area until now.Based on the previous data and field geological survey, this paper discusses theQuaternary strata and active tectonic characteristics of Lianghe basin and Yingjiangbasin, and achieves the main progress as follows.This paper uses geological survey and section measuring, and sets upstratigraphic sequence on the base of the characteristics of Quaternary sediment types,geomorphology, matrrial composition, space distributing law, contact relation andattitude. Studies have been conducted to devide the Quaternary sedimentary strata forthese two basins, with4series,3formations and6members for Lianghe basin, and4series and2members for Yingjiang basin.By carefully studying these two basins`geomorphic feature and evolution, wecan correctly identify7terraces for Lianghe basin and4terraces for Yingjiang basin.specifically, the fifth and sixth terraces of Lianghe basin are lacustrine sediment, andthe others are fluvial deposition. These two basins are part inheritance Quatrtnaryfault basin, evoluting with four stages (valley, lake basin, disappearing of lake-basin,intermontane river). Each stage is closely associated with tectonic movement.By carefully studying the geometric structure, kinematical characteristics and dating results (C14and OSL), we can correctly divide the Dayingjiang Fault to twosegments——Yingjiang fault in the south and Lianghe fault in the north. Yingjiangfault is a Holocene NE-SW sinistral stike-slip fault. But Lianghe fault is a latePleistocene normal fault, and the fault strike changes from NE-SW to N-S. Using theformula, we can calculate the horizontal slip rate3.18±1.23mm/a，the vertical slip rate0.008±0.005mm/a.By carefully studying the trench and dating results (C14and OSL), we cancorrectly identify three palaeoseismic events. The latest palaeoseismic event is about2ka from nowadays, occurring within Yingjiang fault. the second palaeoseismic eventis about7ka from nowadays, occurring within Yingjiang fault. And the thirdpalaeoseismic event is about30ka from nowadays, occurring within Yingjiang faultand Lianghe fault.