Deep control factors of geothermal fields in the northern Songliao Basin based on magnetotelluric survey

The Songliao Basin, located in the eastern part of the Central Asian Orogenic Belt, is influenced by the superposition of multiple structural systems. To investigate the deep thermal driving mechanisms and heat transfer processes, a regional array of 107 magnetotelluric (MT) sites was deployed. And a three-dimensional resistivity model of the northern basin was constructed using a nonlinear conjugate gradient inversion algorithm. High-conductivity anomalies (~ 5 Ω·m) in the shallow sedimentary layers are interpreted as the geothermal caprock and shallow reservoirs. High-resistivity bodies (~ 1000 Ω·m) at depths of ~5 km are inferred to represent the crystalline basement, which may act as a deep geothermal reservoir. In the lower crust and upper mantle, block-like conductive anomalies (~ 5 Ω·m) are interpreted as two heat sources, likely associated with mantle upwelling and deep crustal magmatic activity. Vertically distributed conductive zones (~ 5 Ω·m) in the upper crust delineate major fault systems that serve as fluid and heat migration pathways. Based on the spatial configuration of heat sources and reservoirs, four types of heat transfer models are identified. The central downwarp is characterized by a dual-reservoir and multi-source configuration, corresponding to the strongest heat flow. Comparison between heat flow and formation temperatures indicates that deep thermal reservoirs exert a stronger control on subsurface temperature distribution than shallow reservoirs. These findings provide new insights into the geothermal system architecture of the Songliao Basin and offer a framework for understanding heat transfer processes in similar sedimentary basins.