Abstract: The Aershan volcanic group has been active since the Pleistocene to the modern and has potential to erupt, so it is of great significance to strengthen the study on the Aershan volcano group and evaluate its activity. The magmatism is characterized by low resistivity in electrical properties. The electrical structure obtained by magnetotelluric sounding can be used to study the magmatic occurrence and volcanic activity. It is an effective method to detect the deep structure of volcanic area. Based on the magnetotelluric sounding data of the Aershan volcanic group, the two-dimensional nonlinear conjugate gradient inversion is obtained after the normalization of the data and the two-dimensional electrical structure of the Aershan volcanic group is obtained. It is found that there is a large-scale "arch-bridge" low-resistivity anomaly (resistivity less than 320Ω·m) and there are obvious high-conductivity anomalies (resistivity less than 40Ω·m) respectively on the west of the town of Ershi and the east of Chaihe town, the former is relatively small in sizes, buried at the depth of 40~60km, and the size of the latter is larger, buried at the depth of 60~90km, or even deeper. Combined with geological and geochemical data, it is inferred that the "arch bridge" anomaly is the channel of the basaltic magma transport from the epithermal basins on its both sides. The two high-conductivity anomalies it contains are probably the uncondensed or gathering magma chamber, so the Aershan magma system consists of "arch bridge" channel and asthenosphere-derived basaltic magma, the volcanic group has a unified magmatic system. Further analysis shows that the melting percentage of the "arch bridge" channel material is not less than 0.5%, and the lithosphere structure tends to be stable. The melting degree of the two magma chambers it contains is 2.5%~11.5%, and the grain boundary may all be wetted by the melt, rock flow intensity is relatively low, lithosphere structural stability is poor. In addition, the regional seismic distribution and the formation of hot springs also have a certain correlation to the Aershan volcanic group magma system. There are indications that the Aershan volcano group is in dormancy, rather than an extinct volcano, there is the possibility of eruption, so it should be closely monitored.

Key words: Aershan volcanic group, magnetotelluric sounding, electrical structure, magmatic system, stability analysis

摘要： 阿尔山火山群自更新世至近代持续活动，具有潜在喷发的危险，因此加强对阿尔山火山群岩浆系统的研究，评价火山群的活动性具有重要的意义。在获得阿尔山火山群地区大地电磁测深数据的基础上，对其进行标准化处理后经二维非线性共轭梯度反演，获得二维电性结构成像，发现阿尔山地区岩石圈内部存在大规模的"拱桥式"中、低阻异常（电阻率＜320Ω ·m），并在伊尔施镇西侧和柴河镇东侧分别存在明显的高导异常（电阻率＜40Ω ·m）；前者体积相对较小，埋藏深度在40～60km，后者体积较大，埋藏深度在60～90km，甚至更深。结合地质、地球化学资料，推断"拱桥式"异常为新生代来自两侧盆地软流圈的玄武质岩浆运移的通道，其所包含的2处高导异常，极可能为未冷凝或正在聚集的岩浆房，因此阿尔山岩浆系统由"拱桥式"通道和来自软流圈的玄武质岩浆组成，火山群具有统一的岩浆系统。进一步分析表明，"拱桥式"通道物质熔融百分比≥0.5％，岩石圈结构总体趋于稳定，其所包含的2处岩浆房熔融程度为2.5％～11.5％，颗粒边界可能已被溶体全部润湿，岩石的流动强度相对较低，岩石圈结构稳定性较差。区域地震分布、温泉的形成与阿尔山火山群岩浆系统也具有一定的相关性。综合迹象表明阿尔山群正处于休眠期，并非死火山，有再次喷发的可能，应密切监测。

关键词: 阿尔山火山群, 大地电磁测深, 电性结构, 岩浆系统, 稳定性分析