Geothermal potential of the southern Tianyang basin, northern China, revealed by 3D inversion of magnetotelluric data

Abstract

Tianyang Basin, situated in Northern China, is one of the most significant geothermal fields in the region. While high-temperature geothermal resources within the basin are predominantly concentrated in its northern part, the southern region's potential remained largely unexplored. To investigate the geothermal potential in the southern part of the basin, we conducted a comprehensive magnetotelluric (MT) survey comprising 460 sites across this region. Based on the 3D MT inversion result, we constructed a detailed electrical conductivity model to reveal the deep subsurface electrical structure. The crustal structure of the study area exhibits three distinct layers: the uppermost layer comprises a low-resistance Quaternary sedimentary sequence with conductive anomalies associated characterized by clay alteration zones; the middle layer comprises a high-resistivity Archean metamorphic rock containing several low- resistivity regions (< 20 Ω·m), which are interpreted as geothermal reservoirs at depths of 1–4 km; the bottom layer, extending from 8 to 16 km depth, features a widespread low-resistance zone, potentially attributed to partial melts associated with the Datong volcanic activity, with melt content estimated ranging from 2 % to 7 %. Our investigation revealed distinct heat transfer channels between the heat source and the geothermal reservoirs, characterized by relatively low resistivity and closely correlated with concealed faults in the area. This study not only delineates the spatial distribution of the geothermal system in the southern part of the Tianyang Basin but also provides a scientific foundation for the comprehensive development and utilization of the geothermal resources in the region.