Tectonic and geomorphological characteristics of Laoyingshan in the eastern Sichuan-Yunnan block：Insights into the uplift and rotation of the blocks
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摘要:
印−欧大陆板块的碰撞与挤压造成了青藏高原的隆升和陆内变形，同时引起川滇菱形地块的侧向逃逸与旋转，目前针对川滇菱形地块中部和西部地区的旋转量已进行了大量古地磁研究，但对其东部地区的旋转研究相对缺少。由于河流地貌对地块的旋转量十分敏感，因此，研究利用30 m分辨率的数字高程模型（DEM）提取了川滇菱形地块东部老鹰山地区的22个流域盆地，通过分析其局部地形起伏比、河流纵剖面、河流陡峭指数以及流域方位角4个地貌参数来确定老鹰山地区的地块旋转量和隆升量。研究结果显示：老鹰山地区自晚中新世以来，隆升量约为358 m，隆升趋势为北高南低；河流陡峭指数值整体分布趋势由北向南逐渐降低，高值区主要分布在老鹰山地区北部，低值区主要分布在研究区老鹰山顶部以及老鹰山地区南部；同时根据流域方位角结果表明老鹰山地区旋转量为逆时针旋转15°左右。研究表明自晚中新世以来，川滇地块内元谋断裂以西受走滑断裂影响较小，主要为顺时针旋转；元谋断裂以东受走滑断裂等强烈的左行走滑影响，发生了逆时针旋转并伴随着差异隆升。
Abstract:Objective Since the collision and compression of the Indo-European continental plates, the Qinghai-Xizang Plateau has experienced uplift and intra-land deformationSince the collision and compression of the Indo-European continental plates, the Qinghai-Xizang 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-Xizang 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-Xizang 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.
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Key words:
- block rotation /
- uplift /
- tectonic geomorphology /
- Xiaojiang fault /
- eastern Sichuan-Yunnan block
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图 1 研究区构造简图（Huang et al.，1992；Yoshioka et al.，2003；Tamai et al.，2004；Zhu et al.，2008；Li et al.，2013，2015；Tong et al.，2015；王恒和杨振宇，2019；余华玉等，2023）
Figure 1.
图 8 川滇地块构造活动演变（Tong et al.，2015；吴中海等，2015）
Figure 8.
表 1 大白河、功山大河西侧流域方位角
Table 1. Basin azimuth on the western side of Dabai River and Gongshan River
河流 流域中线方位角/
(°)垂线方位角/
(°)旋转量/
(°)平均旋转量/
(°)1 47.4035 35.5030 11.9005 14.9956 2 56.8472 39.2746 17.5726 3 61.7182 43.5887 18.1295 4 36.7287 24.0545 12.6742 5 34.9060 23.0075 11.8985 6 18.4842 8.4548 10.0294 7 30.4826 13.6866 16.7960 8 31.1446 14.6053 16.5393 9 29.4522 21.8166 7.6356 10 30.9373 14.6053 16.3320 11 26.3950 0.9501 25.4449 
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表 2 大白河、功山大河东侧流域方位角
Table 2. Basin azimuth on the eastern side of Dabai River and Gongshan River
河流 流域中线方位角/
(°)垂线方位角/
(°)旋转量/
(°)平均旋转量/
(°)1 222.3619 206.4810 15.8809 12.2181 2 213.5884 208.1903 5.3981 3 219.7653 208.5652 11.2002 4 229.0780 211.4550 17.6230 5 230.8436 220.5600 10.2836 6 216.6224 203.6995 12.9229
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