Abstract The northern part of the Fennoscandian shield records several Palaeoproterozoic phases of rifting, crustal shortening, metamorphism and structural reactivation. The geologic history has left behind a complex crustal geoelectric structure as evidenced by magnetotelluric (MT) data from the central Finnish Lapland acquired in the context of the MaSca-project in 2014. The data are characterized by strong 3-D effects such as high phase tensor skew values and anomalous induction vectors. Interestingly, however, at the same time a dominant E-W principal direction from the phase tensor data can be inferred. 3-D conductivity models derived using the ModEM code display, high crustal conductance (> 10,000 S) in the vicinity of the Central Lapland Greenstone Belt, the Perapohja Belt and the Kuusamo Belt. Conductors in the northern and southern part of the study area are separated by a resistor coinciding with the Central Lapland Granitoid Complex. A remarkable feature is an arc-shaped conductor inside the northern part of the Central Lapland Granitoid Complex, which continues into the Central Lapland Greenstone Belt in the north. The conductor is associated with a major induction vector anomaly and also coincides with extreme responses (negative phase tensor principal values), which are discussed in an accompanying paper. The conductive structures in the models are interpreted as deeply buried graphite and sulphide bearing metasedimentary rocks or as reactivated Archaean shear zones. The revealed geoelectric structures also partly correlate with seismic reflection and other geophysical data from the area. A possible explanation for the observed pervasive E-W principal direction of the phase tensor data could be the aulacogen (failed rift) suggested in recent tectonic evolution models.

中文翻译：

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芬兰拉普兰 II 中部的大地电磁阵列：3-D 反演和构造意义

摘要 Fennoscandian 地盾的北部记录了几个古元古代的裂谷、地壳缩短、变质作用和构造再活化阶段。2014 年在 MaSca 项目背景下从芬兰拉普兰中部获得的大地电磁 (MT) 数据证明，地质历史留下了复杂的地壳地电结构。这些数据的特点是强烈的 3-D 效应，例如高相位张量偏斜值和异常感应向量。然而，有趣的是，同时可以从相位张量数据推断出主导的 EW 主方向。使用 ModEM 代码导出的 3-D 电导率模型显示，中央拉普兰绿岩带、Perapohja 带和 Kuusamo 带附近的高地壳电导率 (> 10,000 S)。研究区北部和南部的导体由一个与拉普兰中部花岗岩复合体重合的电阻器隔开。一个显着的特征是中央拉普兰花岗岩复合体北部内的弧形导体，该导体一直延伸到北部的中央拉普兰绿岩带。导体与主要的感应矢量异常相关，也与极端响应（负相位张量主值）相吻合，这在随附的论文中进行了讨论。模型中的导电结构被解释为深埋含石墨和硫化物的变质沉积岩或重新激活的太古代剪切带。揭示的地电结构也部分地与该地区的地震反射和其他地球物理数据相关。