THE TECTONIC AND GEOMORPHOLOGICAL CHARACTERISTICS OF NORTHERN JIANSHUI IN THE EASTERN SICHUAN-DIAN BLOCK,IMPLICATIONS FOR UPLIFT AND ROTATIONAL MOVEMENT
The collision and compression between the Indian-Eurasian continental blocks have uplifted and deformed the Tibetan Plateau,forming large-scale strike-slip fault zones and causing lateral escape and rotation of the Sichuan-Yunnan block.Consequently,the Sichuan-Yunnan block is an ideal area to study tectonic uplift and rotation at the southeastern margin of the Tibetan Plateau.Previous studies on rotation in the central and western regions of the Sichuan-Yunnan block have predominantly relied on paleomagnetic research,while studies in the eastern region have primarily used modern observations.Research on historical uplift and rotation in this area is relatively limited.Therefore,investigating uplift and rotation in the eastern part of the Sichuan-Yunnan block will enhance understanding of deformation characteristics across the southeastern margin of the Tibetan Plateau.This paper chooses Jianshui County in the east of Sichuan-Yunnan block as the research area.Jianshui County(23° 12′～24°10′N,102°33′～103°11′E)is located in the south of Yunnan Province.It belongs to Honghe Hani and Yi Autonomous Prefecture of Yunnan Province.The area is sandwiched between the secondary faults of the eastern branch of the Xiaojiang fault and the Heiyi-Xiaoshuijing fault and the Xiaoguan-Lihaozhai fault are developed on the NE sides,respectively.In this study,a 30-meter resolution digital elevation model(DEM)was employed to delineate drainage basins of 10 rivers in northern Jianshui.Analysis of four geomorphic parameters—topographical relief,longitudinal profile,channel steepness index,and basin azimuth—was conducted to reconstruct uplift and rotation in this area.Topographical relief analysis indicates a 275-meter uplift since the Late Miocene,with higher elevation trending eastward and northward.Longitudinal profile analysis shows an average uplift of approximately 78 meters,exhibiting minimal variation.Channel steepness index values are generally low,with higher values in the southeast.Basin azimuth analysis reveals a 19.8° counterclockwise rotation in northern Jianshui.The analysis suggests that since the Late Miocene,the western Sichuan-Yunnan block,west of the Yuanmou fault,has experienced less influence from strike-slip faults,predominantly showing clockwise rotation.Conversely,the eastern region,east of the Yuanmou fault,has undergone significant strike-slip fault activity,resulting in counterclockwise rotation alongside differential uplift.
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