Electrical Structure of Upper Crust in Yongxing Region, Southeast Hunan Province
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摘要: 为了解湘东南永兴地区上地壳地质构造特征及圈定潜在的找矿靶区，对郴州永兴地区的5条大地电磁剖面数据进行了分析与处理，并应用非线性共轭梯度法进行二维反演，获得了该地区上地壳电性结构.结果显示该地区电性分布不均匀，横向上出现高低阻相间分布，纵向无明显电性分层特征.结合湘东南区域地质资料，详细分析了研究区电性结构的地质构造含义.研究表明茶郴断裂带为深大断裂带，控制着研究区内的地质构造及成矿流体上涌通道.根据南岭成矿带铅锌金属矿的成矿规律，结合区域电性结构特征，对研究区内两处铅锌矿体成矿机理与电性结构之间的关系进行了分析讨论.研究结果对认识湘东南永兴地区上地壳的结构特征及寻找潜在矿体具有很好的参考.Abstract: In order to understand the characteristics of the geological structure in the Yongxing region and delineate potential prospecting targets, it investigated the electrical structures of the upper crust in this region using magnetotelluric (MT) data. The electrical resistivity model was obtained by 2D nonlinear conjugate gradient inversion of MT data from five profiles deployed in the Yongxing region of Chenzhou District, Southeast Hunan Province. The results show that the electrical structures are laterally heterogeneous and reveal a subvertical moderate resistivity zone. Combined with the regional geological data of Southeast Hunan, the subvertical resistivity zone is interpreted as the manifestation of the Chaling-Chenzhou fault zone, which controls the geological structure and upwelling channel of ore-forming fluids in the study area. Finally, following structural characteristics of lead-zinc metal deposits in the Nanling metallogenic belt, it discusses the relationship between the metallogenic mechanism and the electrical structures for two existing lead-zinc deposits in the study area.
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图 1 研究区大地构造位置及大地电磁剖面布置
a.华南构造简图，改自文献舒良树（2012）；b.研究区地质构造及大地电磁布设简图
Fig. 1. Tectonic location and profile layout of the MT survey in the study area
图 2 Bahr二维偏离度拟断面
a. L1线；b. L2线；c. L3线；d. L4线；e. L5线
Fig. 2. Pseudosection of Bahr skewness
图 3 5条剖面在6个频点的相位张量椭圆图
Fig. 3. Phase tensor ellipse diagrams of five profiles at six frequency points
a. f=1 000 Hz；b. f=100 Hz；c. f=10 Hz；d. f=1 Hz；e. f=0.1 Hz；f. f=0.01 Hz
图 4 5条剖面电性主轴分析玫瑰图
a. L1线；b. L2线；c. L3线；d. L4线；e.L5线
Fig. 4. Rose diagrams of the orientation of geoelectric strike
图 5 5条剖面每个测点的TE和TM模式的穿透深度
图a~e分别为剖面L1~L5的趋肤深度
Fig. 5. Penetration depth of TE and TM modes at each measurement point of the five profiles
图 6 模型粗糙度、拟合误差随正则化因子变化的曲线
a. L1线；b. L2线；c. L3线；d. L4线；e. L5线
Fig. 6. L⁃curve of RMS values and roughness corresponding to different tau values
图 7 L1剖面视电阻率及相位拟断面对比
Fig. 7. Comparison of apparent resistivity and phase pseudo-section of L1 profile
图 8 L2剖面视电阻率及相位拟断面对比
a. TE模式下实测数据、模型响应的视电阻率及相位拟断面图； b. TM模式下实测数据、模型响应的视电阻率及相位拟断面图
Fig. 8. Comparison of apparent resistivity and phase pseudo-section of L2 profile
图 9 5条剖面中典型测点的视电阻率及相位曲线
Fig. 9. Comparison of observed and predicted MT data representative stations in five profiles
图 10 5条剖面上单点的数据拟合误差
Fig. 10. RMS statistics for each measurement site of the MT profiles
图 11 5条剖面反演结果等值线图
Fig. 11. Cross-section of electrical resistivity model for five MT profiles
图 12 L4与L5剖面的二维电性结构及推断的地质结构
a. L4剖面反演单点拟合差（RMS）；b. L4剖面二维反演电性模型；c. L5剖面反演单点拟合差（RMS）；d. L5剖面二维反演电性模型；e. L4剖面地质断面图；f. L5剖面地质断面图
Fig. 12. 2⁃D electrical resistivity and interpreted geological model
图 13 基于电性结构推断的研究区铅锌矿点成矿动力模型
Fig. 13. Metallogenic dynamic model of lead-zinc deposits in the study area based on electrical structure
表 1 5条剖面的反演参数及数据拟合差统计
Table 1. Inversion parameters and data fitting error statistics for five profiles
测线 反演模式 Tau值 误差限 迭代
次数RMS 视电
阻率相位 L1 TE+TM 7 15% 10% 200 2.74 L2 TE+TM 7 15% 10% 200 2.42 L3 TE+TM 7 15% 10% 200 2.23 L4 TE+TM 5 15% 10% 200 2.46 L5 TE+TM 5 15% 10% 200 2.21 
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