滇西南地区龙陵-澜沧新生断裂带南段的走滑特征与构造转换

The longling-Lancang newly emerging fault zone in southwestern region of Yunnan Province is a typical area to reveal the tectonic activity of late Quaternary and mechanism of strong earthquakes during the deformation of clockwise rotation and limited extrusion in SSE direction of Tibetern block surround the eastern structural core. Based of a promising survey conducted in recent years, correlated with the interpretation of high resolation remote sensing, provides a basis to determine several representative sections in the main active faults for studying at detail. Geological mapping with a large scale, such as 1:5,000～10,000, precise topographic measuring by equipments, such as differential GPS, trench detecting, systematic sampling and dating of the Quaternary deposits will be carried out at the representative sections. By a comprehensive study of late Quaternary tectonic activity, some quantitative parameters of the main active faults will be obtained, such as the detailed structure geometry, geological and geomorphological features, characteristics of movement, strike-slip rates and recurrence intervals of paleoearthquakes and the elapsed time of the last earthquake etc, then judge the risk area or segments to occur large earthquakes in the future. At the same time, based on the analyses of tectonic geomorpholgical features of Cenozoic or Quaternary basins, such as the Lancang, Menglian and Menghun basins, which are controlled by the main active faults in the research area, and the largest horizontal offsets and average strike-slip rates, we can calculate the inception time of right/left-lateral strike-slip motion. Then discuss the tectonic transformation of NE and NW directions of two groups of strike-slip active faults, analyses the kinematic and dynamic mechanism and controlling to strong earthquakes, answer the questions about the inherited and newly emerging features in southern segment of Longling-Lancang newly emerging fault zone.

滇西南地区的龙陵-澜沧新生断裂带是揭示青藏块体绕东喜马拉雅构造节顺时针旋转和物质向南东方向有限挤出过程中晚第四纪构造活动与强震机理的典型地区。本项目拟在前期预研究的基础上，通过高分辨率遥感影像解译、典型地段地质地貌填图、精细地貌测量、探槽开挖和年代样品测试等工作，获得龙陵-澜沧新生断裂带南段主干活动断裂的几何图像、地质地貌特征、运动特性、走滑速率和古地震期次等最新构造活动的定量参数，判识本区未来大震危险区。同时，根据主干活动断裂所控制的澜沧、孟连、勐混等新生代盆地或第四纪盆地构造地貌特征分析，以及断裂沿线最大水平位错量和断裂平均走滑速率估算其发生左旋或右旋走滑的起始时间，进而探讨北东向和北西向两组走滑断裂之间的构造转换关系，分析其构造变形的运动学和动力学机制及其对强震的控制作用，回答龙陵-澜沧新生断裂带的继承性和新生性活动特征。

本项目严格按照课题任务书要求组织实施，科学合理地安排各年度的研究工作，按计划完成了各项研究内容，解决了预设的关键科学问题，取得了预期成果，已正式发表论文5篇，培养硕士研究生2名，达到了提高认识、锻炼队伍和培养人才的目的。取得的主要认识如下：. 研究区内共发育了NE向和NNW向两组活动断裂。其中，NE向孟连断裂和打洛断裂形成历史久，断裂成熟度高，线性特征清晰，以左旋走滑为主。孟连断裂和打洛断裂晚第四纪平均左旋速率分别为2.2±0.4mm/a和1.8±0.9mm/a，其左旋走滑开始时间分别为4.7±1.6Ma和6.2±0.3Ma左右。其最新构造活动和地震活动具有继承性。沿NE向孟连断裂和打洛断裂发育了较为典型的走滑活动控制的晚新生代盆地，属走滑断裂两侧的压剪性/张剪性盆地。通过对勐滨盆地晚新近纪沉积地层的对比分析，其构造变形时间大约为7.78-6.25Ma左右，这与孟连断裂走滑活动的起始时间大体吻合。打洛断裂沿线发育了景洪盆地、景栋盆地等走滑断裂端部的张剪性盆地。. 本区NNW向澜沧断裂和黑河断裂形成历史晚，断裂成熟度低，线性延伸差，性质以右旋走滑为主，其最新构造活动具有新生性，可切割先存的孟连断裂和打洛断裂等，形成网格状断裂分布格局。澜沧断裂和黑河断裂晚第四纪平均右旋走滑速率分别为4.2±0.6mm/a和3.54±0.78mm/a，其右旋走滑开始时间分别为1.3-1.0Ma和0.94-0.56Ma左右。本组断裂的新构造活动既导致了多期古地震事件，还控制了多次7级以上地震的发生，其最新构造活动和地震活动具有新生性。. 澜沧断裂沿线发育了澜沧、勐满、勐遮和勐混等规模较小的第四纪盆地。通过对澜沧盆地第四系沉积地层的岩性和岩相对比分析，发现下中更新统沉积地层发育生长地层的起始时间大约为2.6-1.8Ma，与澜沧断裂右旋走滑的时间相当或略早。. 在青藏高原围绕喜马拉雅东构造结传旋转和向南挤出作用下，北东向的孟连断裂和打洛断裂等开始左旋走滑活动可能与红河断裂右旋走滑导致的区域构造变形有关。而龙陵-澜沧新生断裂的形成主要受北东向左旋走滑断裂书斜式顺时针旋转控制。