【作者】 黄颖；

【导师】 翁爱华；

【作者基本信息】 吉林大学 ， 地球探测与信息技术， 2019， 硕士

【摘要】 大地电磁测深法可获得中国东北地区的深部导电信息,为研究岩石圈结构和厚度提供重要依据,可以帮助认识东北地区的构造演化历史、火山地震活动以及深部动力机制等问题。针对大地电磁三维反演结果光滑连续性变化导致的边界不清晰问题,通过使用非监督的聚类方法分析东北地区大地电磁三维反演结果,提高对岩性与构造边界的刻画能力,进而提高对中国东北地区岩石圈结构的认识。对基本覆盖中国东北地区的82个长周期大地电磁测深点得到的有效阻抗张量信息,通过高斯-牛顿三维反演计算,得到东北地区可靠的深度400km以上的三维电导率模型。根据东北地区反演模型电阻率值的分布和各种聚类分析方法的特点,本文选择使用K均值聚类方法对反演模型电阻率值进行聚类分析。在K均值聚类分析过程中,采用了RS指数指导选择聚类数目,Kaufman法进行中心初始化并最终得到有效的模型聚类结果。本文通过分析三维电导率模型及反演模型的K均值聚类结果,研究东北地区岩石圈厚度和结构特征。根据聚类分析结果,中国东北地区岩石圈底部聚类电阻率大约为339Ωm,其中松辽盆地岩石圈最薄,约60km;大兴安岭地区最厚,约150km;佳木斯地体厚度约为100km;而长白山地区岩石圈厚度不易确定,可能受新生代构造活动影响,电阻率明显减小。研究结果表明,中国东北地区岩石圈结构变化复杂,不同区域电性结构差异明显。其中大兴安岭地区岩石圈整体表现为高阻特征,高阻层连续且厚度大,反映出兴安地块岩石圈结构相对比较稳定。松辽盆地岩石圈发生过减薄作用,结构复杂、厚度小,在上中地壳以中低阻特征为主,在岩石圈下部呈现高阻特征且底界面变化大。岩石圈下方向上存在多个高导体,推测为松辽盆地岩石圈发生拆沉作用而引发的软流圈地幔上涌热物质。佳木斯地块岩石圈具有分层结构,地壳以低中阻特征为主,岩石圈地幔表现高阻特征并向西俯冲至松嫩地块下方。聚类分析算法通过对大地电磁三维反演结果中的地质构造进行有效地识别和归类,提高了对大地电磁反演结果和东北地区岩石圈电性结构的认识。更多还原

【Abstract】 The deep conductive information of the northeastern China can obtained by magnetotelluric(MT)which provides an important basis for studying the structure and thickness of the lithosphere.It can help to understand the tectonic evolution history,volcanic seismic activity and deep dynamic mechanism of the Northeast China.Aiming at the problem of boundary unclearness caused by the smooth continuity of magnetotelluric three-dimensional(3-D)inversion result,the unsupervised clustering method is used to analyze the 3-D inversion results of magnetotelluric in the Northeast China,and the ability to characterize lithology and structural boundaries is improved.And thus the understanding of the lithosphere structure in northeastern China can be improved.Effective impedance tensor information is obtained from 82 long-period magnetotelluric sites which are covering the Northeast China.Through Gauss-Newton 3-D inversion calculation,a reliable 3-D conductivity model with depth of more than 400 km in Northeast China is obtained.According to the distribution of resistivity values of the Northeast China 3-D models and the characteristics of various clustering analysis methods,we chooses to use K-means clustering method to analyze the resistivity values of inversion model.In the K-means clustering analysis process,the RS index is used to guide the selection of the clustering number and the Kaufman method is used to initialize the clustering centers,and we finally obtained an effective clustering result.This paper studies the structure and the thickness of the Northeast China lithosphere by analyzing the electrical structure of the 3-D conductivity model of the Northeast China and the K-means clustering results of the inversion model.According to the results of cluster analysis,the result shows that the cluster resistivity at the bottom of the lithosphere in Northeast China is about 339Ωm.The lithosphere of Songliao Basin is the thinnest,about 60 km;the lithosphere of Great Xing’an Range is the thickest,about 150 km;Jiamusi Block is about 100 km;and the lithosphere thickness of Changbai Mountain Range is not easy to determine,which may be influenced by Cenozoic tectonic activities,and its resistivity is obviously reduced.The research results show that the overall structure of the Northeast China lithosphere is complex,and the electrical structure of different regions have obviously difference.The lithosphere of Great Xing’an range is characterized by high resistivity,and the high-resistivity layer is continuous and thick,and the resistivity is high,reflecting that the lithosphere structure of Xing’an block is relatively stable.The lithosphere of the Songliao Basin has undergone thinning,complex structure and small thickness.The upper and middle crust of Songliao Basin are mainly characterized by medium and low resistivity.The lower Songliao Basin lithosphere exhibits highresistivity characteristics and its interface changes greatly.A number of conductors are developed upwards below the the Songliao Basin lithosphere.We speculate that it is related to asthenosphere mantle upwelling caused by the delamination of Songliao Basin lithosphere.The lithosphere of the Jiamusi block has a layered structure.The crust is dominated by low and medium resistivity and the lithosphere mantle exhibits highresistivity characteristics and subducts westward below the Songnen block.The cluster analysis algorithm effectively identifies and classifies the geological structures in the 3D inversion results of magnetotelluric,and improves the understanding of the magnetotelluric inversion results and the lithospheric electrical structures in Northeast China.更多还原