| 湘西北民乐毗邻区深部电性结构及其地质意义 |
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| 引用本文：曹创华,邹光均,彭杰,楼法生,邓居智,孟德保,康方平,文春华,李坤鹏,韩中骥.2020.湘西北民乐毗邻区深部电性结构及其地质意义[J].地球学报,41(2):219-229. |
| DOI：10.3975/cagsb.2020.021301 |
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| 基金项目:国家重点研发计划“深地资源勘查开采”重点专项课题(编号: 2017YFC0601506);湖南省自然科学基金“基于中心阻抗响应的大地电磁反演及应用研究”(编号: 2020JJ3136);中国地质调查局“湖南花垣-凤凰地区铅锌矿整装勘查区矿产调查与找矿预测” (编号: 121201004000172201-22) |
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| 中文摘要:为揭示湘西北民乐毗邻区南华纪大塘坡组含锰沉积地层结构, 深化对地堑-地垒成锰地质空间的认识, 实现地球物理深地探测技术对南华纪沉积型锰矿床的找矿指导, 对区内经过民乐锰矿的大地电磁测深剖面进行了处理和解释, 结合地质信息反演了南华纪古盆地地层构造格局。首先通过频率域大地电磁探测数据进行了阻抗张量和相位张量分解分析, 揭示了湘西北民乐地区在高频区(大于0.01 Hz)主要呈现二维构造特征; 其次利用Swift分解和相位张量分解结果对剖面所有测点数据进行了电性主轴分析, 判断了剖面主要构造走向总体上呈北偏东37°, 计算了TE、TM两个极化方向的卡尼亚视电阻率和相位; 最后针对TE、TM两个模式利用Occam反演方法分别进行了单独和联合反演, 得到了民乐地区深部电性分布并进行了地质解释。研究结果表明: 湘西北民乐地区由浅至深电性结构比较简单, 地层由新到老分层性较好, 大体可分为高台组白云岩中阻层、清虚洞组灰岩高阻层、石牌组—牛蹄塘组低阻层、留茶坡组—陡山沱组较高阻层、南沱组—大塘坡组低阻层、古城组和富禄组中阻层6层; 大地电磁反演电阻率模型等值线图中的“凹中凹”地层结构是圈定成矿靶区的主要地球物理标志; 民乐—花垣一带为古天然气渗漏口的过渡相和边缘相, 含锰地层具有越往东北向埋深越浅、厚度也越来越薄的特点。 |
| 中文关键词:湘西北地区 大地电磁测深 南华纪 沉积盆地 锰矿 |
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| Deep Electrical Structure in the Neighboring Areas of Minle in Northwestern Hunan Province |
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| Abstract:In order to reveal the manganese-bearing sedimentary stratigraphic structure of the Datangpo Formation of Nanhua Period in the neighboring areas of Minle in northwestern Hunan Province, deepen the understanding of the geological space for horst-graben manganese mineralization, and realize the geophysical deep-exploration technology for the Nanhua sedimentary manganese deposit, the authors, according to the prospecting guidance, processed and explained the magnetotelluric sounding profile passing through the Minle manganese deposit in the study area, and inferred the stratigraphic structure of the Nanhua Jigu Basin in combination with geological information. Firstly, the impedance tensor and phase tensor decomposition analysis was carried out by the frequency domain magnetotelluric detection data, which reveals that the Minle area in northwestern Hunan mainly exhibits two-dimensional structural features in the high frequency region (greater than 0.01 Hz); secondly, the authors used Swift decomposition and phase tensor to investigate the decomposition results of the electric spindle analysis of all the survey data of the section. It is judged that the main structural trend of the section was generally 37° eastward; in addition, the apparent resistivity and phase of the two polarization directions of TE and TM were calculated. Finally, for the TE and TM modes, the Occam inversion method was used to perform separate and joint inversion, and the deep electrical distribution of the Minle area was obtained and geological interpretation was carried out. The results show that the shallow to deep electrical structure of Minle area in northwestern Hunan is relatively simple, and the strata are well stratified from new to old. The strata can be roughly divided into six layers, i.e., the middle layer of the Gaotai Formation dolomite and the high-resistance layer of the Qingxudong Group limestone, Shijia Formation–Niuhutang Formation low resistance layer, Liuchapo Formation–Doushantuo Formation higher resistance layer, Nantun Formation–Datangpo Formation low resistance layer, Gucheng Formation and Fulu Formation middle resistance layer. Magnetotelluric inversion shows that the “concave-concave” stratigraphic structure on the contour map of the resistivity model is the main geophysical marker for the ore-forming target area, that the Minle–Huayu area is the transitional phase and the marginal facies of the paleo-natural gas seepage, and that the manganese-bearing strata have the feature that the shallower the depth, the thinner the thickness northeastward. |
| keywords:northwestern Hunan Province magnetotelluric sounding Nanhua Period sedimentary basin manganese ore |
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