Magmatic Geothermal Genesis Model in the Huailai Area Based on the Constraints of the Crust–Mantle-Scale Geoelectric Structure

Abstract

The Huailai area is rich in geothermal resources, but the formation mechanism of its deep heat source is still unclear. In this paper, based on 16 broadband magnetotelluric sounding points, the two-dimensional electrical structure of the crust and mantle in the Huailai area was obtained. Combined with deep seismic reflection and P-wave seismic tomography, the geophysical characteristics of deep heat sources and reservoirs in the Huailai area are described. The Huailai area is characterized by low resistivity and layered reflection above 2 km in depth, which shows the distribution of the Cenozoic sedimentary cover layer. The upper crust is characterized by high resistivity without an obvious reflector, corresponding to the crystalline basement of the basin, whose main lithology is Archean gneiss. There is a highly conductive and bright-spot-reflective structure under the basement, which extends to 100 km, indicating the upwelling of mantle-derived material. Combined with the results of helium isotope tracing, a magma-type geothermal model in the Huailai area is proposed. The upwelling mantle-derived magma material is enriched under the basement to form a heat source. The heat is transferred to the upper crust through heat conduction along the crystalline basement. Then, groundwater circulation brings deep heat to the surface, forming hydrothermal resources.