Revealing deep heat transfer characteristics of the Yalu River Basin using joint magnetotelluric and gravity inversion

The Yalu River Basin (YRB), located in northeastern China, lies along the western margin of the Changbaishan volcanic system and hosts the intraplate monogenetic Longgang volcanic. To investigate the deep heat transfer mechanisms of the geothermal systems in this region, we performed sequential joint inversion of magnetotelluric (MT) data from 110 sites and gravity data collected in a grid-based layout. The resulting 3D resistivity and density models reveal a pronounced structural contrast across the Yalu River Fault (YRF). North of the YRF, in the Longgang block, the middle-to-lower crust exhibits both low-resistivity and high-density, consistent with the presence of mantle-derived magmatic intrusions. In the upper crust, a dual-reservoir structure composed of shallow limestone and deeper granitic formations with high-resistivity characteristics. In contrast, the crust of the Helong block, located on the northern side of the YRF, shows high-resistivity and low-density, primarily attributed to granitic intrusions.

These structural differences indicate two distinct modes of heat transfer. In the Longgang block, the crust is relatively ductile and has experienced significant deformation due to the subduction of the Pacific Plate. This setting facilitates the rapid ascent of deep magmas and enables trans-lithospheric heat transport. In the Helong block, by contrast, the crust is mechanically stronger and less deformed, limiting the vertical migration of magma. Here, heat is primarily generated by radiogenic decay within granitic intrusions, which warms meteoric water stored in fractured reservoirs, resulting in surface thermal anomalies and forming a crustal-circulation-based heat transfer model. These contrasting mechanisms highlight the influence of crustal deformation and tectonic setting on the development of geothermal systems in intraplate volcanic regions.