Three-dimensional magnetotelluric inversion reveals the typical geothermal structure of Yanggao geothermal field in Datong Basin, northern China

Abstract

The Yanggao geothermal field, located in the north of the Datong Basin, and close to the Datong Volcanic Group, the geothermal field is affected by deep faults and vigorous tectonic activity. Yanggao has abundant geothermal resources, and contains a large number of hot springs. To explore the geothermal system and characterize the formation mechanism of the Yanggao geothermal field, we deployed 168 magnetotelluric (MT) sitesin the study area. MT phase tensor analysis is used to estimate the dimensionality of the subsurface. Furthermore, we conducted an inversion of the MT data to establish a 3D resistivity model of the study area. The results suggest that the Yanggao geothermal system can be divided into three layers. A low-resistivity layer (C1) exists at a depth of 2 km, which can be interpreted as the clay alteration layer (clay cap) and the reservoir of the geothermal system. Under the reservoir, the model indicates an additional low-resistivity zone (C3) at a depth of 8 km, which is presumed to be a heat source related to the Datong Volcanic Group. Moreover, a vertical low-resistivity zone (C2) between the reservoir and the heat source is related to the Yunmenshan Fault acting as a heat conduction path in the Yanggao geothermal field, controlling the infiltration and recharge of the hot springs.