Deep structure and geothermal resource effects of the Gonghe basin revealed by 3D magnetotelluric

Abstract

In order to better understand the crustal shortening and orogenic uplift in the northeastern margin of the Tibetan Plateau, as well as the geothermal resource effects formed during this process, we used ModEM software to perform 3D MT imaging on broadband magnetotelluric survey points deployed at 710 points in the Gonghe Basin and its surrounding areas. The resistivity model suggests that the Gonghe Basin exhibits a low–high–low overall electrical structure, with high conductivity widely distributed in the middle and lower crust. The resistivity model also reveals a significant discontinuity between high and low resistivity blocks at various depths in the upper and middle crust. These discontinuities are align with the faults observed on the surface related to strong crustal fluctuations, which are connected to high conductors in the middle and upper crust. Using empirical formulas for high-temperature and high-pressure testing of granite, it is estimated that the melting volume of these high conductors ranges from 3 to 43%, demonstrating good "plasticity". These high conductors can act as detachment layers for crustal shortening and deformation during the expansion of the Tibetan Plateau towards the northeast edge and can continuously conduct heat energy upwards, creating a high thermal background in the Gonghe Basin.