Deep structure and geothermal genesis model of Xiong’an New Area, Northern China: Insights from 3D joint inversion of magnetotelluric and gravity data

• A 3D structural model of the entire Xiong'an New Area at depths of <10 km. • We revealed the 3D spatial distribution of deep geothermal reservoirs, cap rocks, heat-controlling and water-conducting faults in Xiong'an New Area. • We established a geothermal genesis model and evaluated the geothermal potential of different geothermal fields. Xiong'an New Area is one of the regions with the most favorable geothermal conditions in northern China, particularly with significant geothermal potential in the depths. However, past studies have focused on the identified geothermal fields, lacking exploration into the deep structure across the entire region, thus limiting the assessment of different geothermal fields and potential geothermal resources. We utilized magnetotelluric and gravity data in Xiong'an New Area and its surrounding regions to conduct 3D joint inversion. The geophysical model reveals the structure above 10 km depth. The depth of the deep thermal reservoir's top boundary ranges from 600 to 2500 m in the Rongcheng and Niutuozhen uplifts, 3000 to 4000 m in the Gaoyang low uplift, and exceeds 3500 m in other regions. The heat-controlling and water-conducting faults are identified, which control the structural patterns of the region. We established a deep geothermal genesis model for Xiong'an New Area. Influenced by mantle heat sources and radiogenic heat production, the Rongcheng and Niutuozhen geothermal fields feature Neogene strata as the caprock, with faults serving as water and heat conduits, and relatively shallow Wumishan Formation acting as thermal reservoirs. Conversely, the Gaoyang geothermal field has Neogene and Paleogene strata as caprock, controlled by faults and deeper thermal reservoirs. We conducted 2D steady-state heat conduction simulations. It was confirmed the differentiated structure was the key reason for the "high in the north, low in the south" geothermal field characteristics, and the depth of Gaoyang geothermal field (>3 km) may have greater geothermal potential.