滇中地块新生代晚期的变形机制:基于构造地貌学分析

滇中地块位于青藏高原东南缘，是研究青藏高原东南缘新生代晚期构造变形机制的理想场所. 滇中地块新生代晚期的变形机制主要有“下地壳流”和“刚性块体挤出”两种模式，前者认为地块构造活动分布较为均匀，后者认为构造活动沿断裂带更为强烈. 由于地貌指数对构造活动非常敏感，为厘定研究区新生代晚期的变形机制，基于30 m分辨率的SRTM?3数字高程模型（DEM）提取了滇中地区319个（亚）流域盆地，通过分析获得了面积高程积分曲线及面积高程积分（HI）、流域形状指数（BS）、流域盆地不对称度（AF）、标准化河流阶梯指数（SLK）、谷底宽度与谷间高度比（VF）这5种地貌指数，综合这五种指数得出相对活动构造指数（I_at），并利用构造地貌指数（I_at）揭示了研究区的相对构造活动分布特征. 研究表明丽江-小金河断裂带、则木河-小江断裂带、红河断裂带及金沙江两侧的I_at值相对较小，其他部位相对较高，这表明滇中地区的构造活动性强的区域主要集中发育在断裂带附近，与“刚性块体挤出”模式相一致. 滇中地块中部的金沙江两侧I_at值相对较低，表明其地貌活动性较强. 这是由于新生代晚期青藏高原东南缘的隆升及河流重组，导致的金沙江及其支流切割力增强，从而造成金沙江两侧HI值、BS值、SLK值增高和VF值降低，使得金沙江两侧I_at值相对较低. 

The Mechanism of Tectonic Deformation of the Central Yunnan Terrane in the Late Cenozoic Based on Tectonic Geomorphology

The Central Yunnan Terrane, with internal faults developed, is located in the Southeast of the Tibetan Plateau, which is an ideal place to study the Cenozoic tectonic deformation mechanism of this area. The Cenozoic deformation mechanism of the Central Yunnan Terrane is controversial, and there are two main types of deformation mechanism: "lower crustal flow" and the "rigid block extrusion". The former proposed that the tectonic activity of the block is more uniform, and the latter proposed that the tectonic activity is more intense along the fault. The tectonic activity of different mechanisms has different responses on the surface, and the geomorphic index is extremely sensitive to the tectonic activity response. To determine the tectonic deformation mechanism of the Cenozoic in this study area, 319 basins (sub?basins) were extracted based on the SRTM?3 Digital Elevation Model (DEM) with a resolution of 30 m. Indices used include hypsometric curve and hypsometric integral (HI), drainage basin shape (BS), asymmetric factor (AF), normalized stream?length gradient (SLK), and the ratio of valley floor width to valley height (VF). Results from the analysis are accumulated and expressed as an index of relative active tectonics (I_at), which we divide into four classes from relatively low to highest tectonic activity. The results are: The Iat values of the Lijiang?Xiaojinhe fault zone, Zemuhe?Xiaojiang fault zone, and Red River fault zone in the Central Yunnan are relatively small, and they gradually increase from north to south, which is consistent with the "rigid block extrusion" mode. At the same time, the Iat value on both sides of the Jinsha River is relatively low it shows that the geomorphic activity is strong, which may be due to the uplift of the Central Yunnan block and river system reconstitution, and the resulting knick points are transmitted upstream. During the migration of the cracks, they are transmitted from the main river channel to the secondary river channel, which affects the increase of the HI, BS and SLK value and the decrease of the VF value, making the relative tectonic activity stronger.