| 滇西地壳三维密度结构及其大地构造含义 |
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| 引用本文： | 杨文采,侯遵泽,于常青.滇西地壳三维密度结构及其大地构造含义[J].地球物理学报,2015,58(11):3902-3916. |
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| 作者姓名： | 杨文采 侯遵泽 于常青 |
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| 作者单位： | 大地构造与动力学国家重点实验室, 中国地质科学院地质研究所, 北京 100037 |
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| 基金项目： | 中国地质调查项目(12120113093800)资助. |
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| 摘 要： | 重力异常揭示地壳三维密度结构是地球物理的重要目标和任务,其关键技术是密度反演.本文对滇西地区重力异常进行了多尺度密度反演,首先利用小波变换对重力异常进行多尺度分解,接着利用功率谱分析方法估算各层场源的平均深度,然后利用广义密度反演方法进行各层密度反演,取得区域地壳多个深度上的密度扰动图像.滇西上地壳高密度扰动出现在扬子克拉通内部和西缘,以及澜沧江断裂带西缘,后者对应昌宁—勐连蛇绿混杂岩带及岛弧岩浆岩带.上地壳低密度异常主要反映西昌裂谷带和高黎贡—腾冲一带的岩浆房,和兰坪—思茅盆地中的坳陷带指示钾盐等沉积矿产目的层较厚的区段.滇西上地壳和中地壳出现三条低密度扰动带,与三期大陆碰撞带的吻合.大部分6级以上地震分布在低密度异常区或它们的边缘,只有在西昌—元古谋裂带才分布在高密度异常区.克拉通内部古裂谷带地震可分布在高密度异常区.在26°N线以南下地壳为高密度区,以北为低密度区.因此,26°N线的一个属性是下地壳密度差异分界线.滇西由北向南地壳加厚缩短的程度是逐渐变弱的,在26°N线以南,南北向的地壳加厚缩短就不明显了.高黎贡走滑剪切带、澜沧江走滑剪切带、红河走滑剪切带在滇西中地壳密度扰动平面图中表现为密度急变的梯度带.表明这三条主要的走滑剪切断裂带都穿过中地壳并可能延深到下地壳.
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| 关 键 词： | 区域重力场 小波多尺度分解 密度反演 地壳密度结构 中国滇西 |
| 收稿时间： | 2014-10-19 |
3D crustal density structure of West Yunnan and its tectonic implications |
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| YANG Wen-Cai,HOU Zun-Ze,YU Chang-Qing.3D crustal density structure of West Yunnan and its tectonic implications[J].Chinese Journal of Geophysics,2015,58(11):3902-3916. |
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| Authors: | YANG Wen-Cai HOU Zun-Ze YU Chang-Qing |
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| Institution: | State Key Lab of Continental Tectonics and Dynamics, Institute of Geology, CAGS, Beijing 100037, China |
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| Abstract: | The crustal structure of West Yunnan is associated with the collision between the Eurasia and India plates. Though some geophysical profiles have been performed to reveal the lithospheric structure, but very few work on deep mapping of this area have been done. We study 3D crustal density disturbance of this area and present corresponding maps for the upper, middle and lower crust respectively.#br#We apply the method called the multi-scale analysis for delineation of density disturbances of the crust at different depths. The method of regional gravity data processing have been developed by our group, combining theories based on multi-scale wavelet analysis, spectral analysis of potential fields and geophysical inversion. The multi-scale analysis contains three modules, which are spectral analysis for division of density layers, decomposition of the field by using wavelet transformation and multi-scale analysis, depth estimation and density inversion of decomposed gravity anomalies. The wavelet analysis produces wavelet details that correspond to some equivalent layers, the spectral analysis computes the depths the equivalent layers, and the inversion produces density disturbance maps on planes of different depths.#br#Applying this method to the West Yunnan region, we obtain 4 density disturbance maps corresponding to depths 4.5 km, 7.8 km, 24.2 km and 48.6 km. The map of the upper crust shows that low density anomalies correlate with magmatic thumbs and depressions in sedimentary basins, which belong to the target-areas for sylvinite ore exploration. Three low-density zones of trending north-south occur in the lower and middle crust, corresponding to the 3 stages of terrane collisions between the Yangtze, Indu-Sino, West Burma, and India cratons. The map of the lower crust indicates that the latitude line of 26°N is a density separation line in the lower crust, as low-density area appears on its north and high-density area appears on its south. The crustal thickening and shortening caused by collision between Eurasian and India plates decrease from north to south, and turn to eliminate in the south to the line of 26°N latitude. On the density disturbance maps, the main slide-shear fault zones, including the Gaoligong, the Lancang River and Red River, are delineated by sharp density-variation zones, proving they are cut into the middle crust and probably extend down to the lower crust.#br#The method of multi-scale analysis is a new method of regional gravity data processing and demonstrates its potential power for delineation of crustal structure and division of secondary tectonic units in the West Yunnan region, providing some new evidence for understanding the deep structure in the study area. |
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| Keywords: | Rregional gravity field Wavelet transformation Multi-scale analysis Density inversion Crustal density structure West Yunnan |
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