滇西地区云县一宁蒗剖面二维速度结构与构造特征研究

发布时间：2019-05-03 18:33

【摘要】：滇西地区由于其复杂的地质结构,历史上频繁的地震活动以及与藏南地区深部的紧密联系,长期以来是地球物理学家重点研究区域。红河断裂作为滇西地区规模巨大的构造带,对整个滇西地区的地质活动有着重要的影响。该区域开展了大量的地球物理探测研究工作,但是对红河断裂不同区段的深浅部构造特征并未形成良好的控制。为了对红河断裂及周围地区地壳上地幔结构进行深入研究,在滇西地区穿过红河深大断裂带我们完成了一条由云县至宁蒗近南北向长300km的宽角地震反射／折射剖面。该剖面的中南段跨越了红河断裂,而在北段则平行于程海断裂,同时剖面南段还与南定河断裂、澜沧江断裂、无量山断裂斜交。结合初至波走时成像及正演建模方法,我们对该测线观测数据进行一维、二维分析拟合,获得了该地区沿测线的二维地壳P波速度结构模型。结果显示：整个地壳可分为上地壳、中地壳、下地壳三层；它们的界面有一定的起伏变化,上地壳埋深：14.5—15.8km;中地壳埋深为：27.1-31.Okm,下地壳埋深为：45.0-54.0km；各层P波速度变化范围分别：6.02-6.23km/s,6.20-6.55km/s,6.49-6.90km/s。沿测线Moho界面埋深存在较大横向变化,自南向北明显变深,南侧Moho埋深约为45km,北侧Moho埋深可达54km,较之典型大陆地壳,存在明显增厚现象；而沿测线中上地壳厚度变化不大,地壳增厚主要缘于下地壳厚度的增加；以红河断裂为界,地壳结构在横向存在明显差异,暗示了红河断裂作为扬子准地台和三江地槽系构造边界的作用；测线穿过区域红河断裂两侧没有明显的Moho埋深变化,结合临近区域的其他研究结果,表明红河断裂在不同区段存在较大差异。
[Abstract]:Because of its complicated geological structure, frequent seismic activity in history and close connection with the deep part of southern Tibet, the western Yunnan area has long been the key research area of geophysics. As a large-scale tectonic belt in western Yunnan, the Honghe fault has an important influence on the geological activity of the whole western Yunnan area. A great deal of geophysical exploration has been carried out in this area, but the deep and shallow structural characteristics of different sections of the Red River fault have not been well controlled. In order to study the crust and upper mantle structure of the Honghe fault and its surrounding area, we have completed a wide angle seismic reflection / refraction profile from Yunxian to Ninglang near the north-south direction of 300km in the deep and large fault zone of Honghe in western Yunnan. The middle-south section of the section crosses the Honghe fault, while in the north section it is parallel to the Chenghai fault. At the same time, the southern section of the section also intersects with the Nanding River fault, Lancang River fault and Wulangshan fault. Combined with the travel-time imaging and forward modeling method of the first break wave, we performed one-dimensional and two-dimensional analysis and fitting of the observed data of the survey line, and obtained the two-dimensional P-wave velocity structure model of the crust along the survey line in this area. The results show that the whole crust can be divided into three layers: upper crust, middle crust and lower crust. The upper crust is 14.5 ~ 15.8 km ~ (m), the middle crust is 27.1 ~ 31.Okm, and the lower crust is 45.0 ~ 54.0km, and the upper crust is 14.5 ~ 15.8 km ~ (m), the middle crust is 27.1 ~ 31.Okm, and the lower crust is 45.0 ~ 54.0km. The variation range of P wave velocity in each layer is 6.02 ~ 6.23 km / m, 6.20 / 6.55 km / m, 6.49 / 6.90 km / s, respectively. The depth of the Moho interface along the survey line has a great lateral variation, and becomes deeper from the south to the north. The Moho depth of the south side is about 45 km, and the Moho depth of the north side is up to 54 km, which is obviously thicker than that of the typical continental crust. The thickness of the upper crust varies little along the survey line, and the thickening of the crust is mainly due to the increase of the thickness of the lower crust. Taking the Honghe fault as the boundary, there are obvious differences in the crustal structure in the lateral direction, which indicates that the Honghe fault acts as the tectonic boundary of the Yangtze quasi-platform and the Sanjiang geosyncline system. There is no obvious change of Moho buried depth on both sides of the red river fault through the survey line. Combined with other research results in the adjacent area, it is shown that the red river fault has great difference in different zones.
【学位授予单位】：中国地震局地球物理研究所
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P315.2

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