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

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