Tectonic and geomorphological characteristics of Laoyingshan in the eastern Sichuan-Yunnan block：Insights into the uplift and rotation of the blocks

Objective Since the collision and compression of the Indo-European continental plates, the Qinghai-Tibetan Plateau has experienced uplift and intra-land deformationSince the collision and compression of the Indo-European continental plates, the Qinghai-Tibetan Plateau has experienced uplift and intra-land deformation. Similarly, the Sichuan-Yunnan block underwent lateral escape and rotationSince the collision and compression of the Indo-European continental plates, the Qinghai-Tibetan Plateau has experienced uplift and intra-land deformation. Similarly, the Sichuan-Yunnan block underwent lateral escape and rotation. Although extensive paleomagnetic studies have been conducted on the rotation of the central and western parts of the Sichuan-Yunnan rhombic block, less attention has been paid to the rotation of its eastern partSince the collision and compression of the Indo-European continental plates, the Qinghai-Tibetan Plateau has experienced uplift and intra-land deformation. Similarly, the Sichuan-Yunnan block underwent lateral escape and rotation. Although extensive paleomagnetic studies have been conducted on the rotation of the central and western parts of the Sichuan-Yunnan rhombic block, less attention has been paid to the rotation of its eastern part. This study employs fluvial geomorphology, which is highly sensitive to mass rotation, to investigate the rotation and uplift in the Laoyingshan region, situated in the eastern part of the Sichuan-Yunnan block. Methods A 30 m resolution digital elevation model (DEM) was used to identify and analyze 22 basins in the study area. Four geomorphological parameters were examined: local topographic relief ratio, longitudinal profile, normalized steepness index, and basin azimuth. Results (1) According to regional topographic relief, the low-relief area in the Laoyingshan region is mainly located near the Sijia River and the Baizai River on the western side, whereas the high-relief area is mainly found near the Dabai River and the Gongshan River on the eastern side of the Laoyingshan. The relief around the Dabai and Gongshan Rivers was greater than that around the Sijia River on the western side of Laoyingshan. (2) The normalized steepness index in the Laoyingshan area gradually decreased from north to south. The high-value areas are primarily located near Awang and Jinyuan, corresponding to the east and west branches of the Xiaojiang Fault. In contrast, the low-value areas were mainly distributed at the top of the Laoyingshan and south of the Baozai River in the study area. (3) The results of the river longitudinal profile indicated that the average surface uplift of the area was approximately 358 m. (4) Based on the results of the watershed azimuth angle, the Laoyingshan area underwent a counterclockwise rotation of approximately 15°. Conclusion The analysis suggests that since the Late Miocene, the western region of the Sichuan-Yunnan block, located west of the Yuanmou Fault, has experienced fewer effects from strike-slip faults and has predominantly undergone clockwise rotation. Conversely, the eastern region of the Sichuan-Yunnan block, influenced by strike-slip faults, underwent counterclockwise rotation with differential uplift. [ Significance] The fluvial geomorphological index outlines the tectonic rotation of the eastern Sichuan-Yunnan block.