The Yadong-Gulu rift (YGR) South Tibet is a Cenozoic active rift, which is endowed with abundant geothermal resources. The Gulu geothermal field (GGF) is located in the Northern section of the rift, where a large number of high-temperature hot springs develop, but its geothermal system is mysterious. In this study, the three-dimensional (3D) electrical structure of GGF is revealed by broad magnetotelluric (MT) and audio magnetotelluric (AMT). MT reveals that middle and upper crust conductors are developed in the subsurface of GGF. The conductors may originate from the partial melting that drives the geothermal system. AMT reveals that the electrical structure of GGF is conductive alternation cap overlying more resistive reservoir, which is consistent with the classical electrical structure of geothermal systems in worldwide active tectonic zones. According to the geothermal system model, cold fluids may converge from the periphery of GGF to the middle, wherein fault F1 (the Western branch of Jiulazi-Sanxung fault) may be the main channel for cold fluids to migrate downward. The fluids are heated by partial melting in the middle and upper crust, and may migrate upward along fault F2 (the middle branch of Jiulazi-Sanxung fault) and develop into heat reservoirs.

By analyzing the characters of the mainstream commercial magnetotelluric inversion softwares in dealing with audio magnetotelluric data, a dynamic model-making method for inversion has been developed based on the observed AMT data. This method focusing on model domain can adjust mesh's scale and model's dimension depending on the field data just with a few parameters. By this, it is convenient to study the geo-electrical anomalies variations of different scale or dimensional models. Applying such model-making technique into the known hardrock geological setting, it is easy to obtain a new geo-electrical model which agrees with the resistivity curves of core samples better than before. It is demonstrated that this can increase the recognition of the resistivity contrast and deserves studying further.

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