| Muchuan Mabian area is located in the southwest of Sichuan Basin and the southeast of Qinghai Tibet Plateau.Under the influence of the compression of Qinghai Tibet Plateau,neotectonic movement in the area is relatively active,which is manifested in terrace development,planation plane development,water system change,landform and seismic activity,reflecting the characteristics and laws of neotectonic movement in the study area.The study of the neotectonic movement characteristics in this area has certain guiding significance for the stability of Sichuan Basin and the late Cenozoic episodic uplift of the eastern margin of the Qinghai Tibet Plateau.The uplift of Neotectonic crust is reflected in the development of planation plane and river terrace in the study area.The study area is located in the front of the development of the fault system in the eastern margin of the Qinghai Tibet Plateau to the interior of Sichuan Basin.Based on the combination of field investigation and indoor information,the geological and geomorphic characteristics and changes,the strata and rocks,and the structural geometry characteristics in the study area are summarized and analyzed on the macro level,and the morphology of quartz particles is studied on the faults and terraces on the micro level with the help of SEM.It is found that there are multi-level planation planes in the study area,of which the well preserved planation planes are mainly three levels,formed in the Pleistocene and in a stepped form.The terraces of different basins in the study area develop in different stages,among which the terrace of Mabian river reach is the most typical,and there are four complete terraces.Except that the first terrace is accumulation terrace,the others are base terrace.The terraces at all levels are 10 m,37 m,50 m and 79 m respectively,forming in Holocene,late Pleistocene,Middle Pleistocene and early Pleistocene,respectively,1.0 ± 0.1 million years ago,10.0 ± 1.2 million years ago,15.0 ± 1.5 million years ago.According to the age and elevation analysis of the terrace,the cutting rate and the surface uplift rate of the river in different periods are obtained.The uplift rates are 0.0431mm/a,0.26mm/a,3mm/a and 10.0mm/a,respectively.Using the gravel statistical method of terrace,it is found that the MabianRiver in the study area has been diverted due to differential uplift.During the Middle Pleistocene,the flow direction of the ancient Mabian river was from the northwest to the southeast.It is speculated that the ancient Mabian river finally flowed into the ancient Jinsha River in the southeast of the study area.From the Middle Pleistocene to the Holocene,the flow direction of the ancient Mabian river changed from the southeast to the North due to the tectonic action,and now it finally flows northward into the Minjiang River Basin.The faults in the study area are mainly north-south and north-west,which are small-scale shallow brittle faults.The active periods of the main faults since Neogene in the study area were studied by means of the etching micro morphology of the quartz particles,and the active mode of the faults was discussed by combining the micro fracture of the surface stress of the quartz particles.In the neotectonic movement period,the main faults in the study area have two periods of concentrated activity: the first period is in Pliocene,the main faults in the study area in the region have been over active,and the second period is in late Pleistocene to Holocene,the regional faults have weak activity in varying degrees.The movement pattern of the main faults in the study area in the recent period is analyzed.It is considered that from the beginning of the Middle Pleistocene to the Holocene,the fault experienced creep movement first and then stick slip movement.From the late Pleistocene to the Holocene,the agate fault and Zhongdu fault move in two ways: stick slip and creep slip. |
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