Regional 3-D electrical resistivity model of Mongolia: Constraining lithospheric properties and architecture

Sumamry Electrical resistivity models derived from magnetotelluric (MT) measurements across the Khangai Dome, an intracontinental plateau in central Mongolia, have identified several intriguing features, including a locally thinned lithosphere and extended fluid-rich domains in the lower crust. However, due to the limited spatial coverage of these studies, whether those features extend beyond central Mongolia could not be assessed. This is an important question with major scientific implications for understanding the geodynamic evolution of the region. The surrounding areas also host significant mineral deposits and geothermal resources, whose origin and interpretation depend on the characterization of deep structures to be fully understood. In this study, we report on MT data from 378 new locations to the west, east, and north of the Khangai Dome, acquired between 2020 and 2023. A new 3-D electrical resistivity model of the region was derived using a combination of the new and previously acquired datasets. This new model covers an area of approximately 900 × 1250 km2, substantially expanding the spatial coverage compared to previous models. The key methodological novelty of this study is the implementation of a recently developed, scalable, and open-source 3-D inverse solver based on the integral equation approach and non-local parametrization. The 3-D model fits the observed data remarkably well, and the recovered features show good agreement with those from previously published models obtained with different solvers and subsets of the data. The model reveals an upper crustal dichotomy, with very high resistivity in the northern region and low resistivity in the southern region. The boundary between these regions follows the Main Mongolian Lineament in the central and eastern regions and the Ikh-Mongol arc system in the western region. In the lower crust, the resistivity is generally lower, and several long, laterally extended, very low-resistivity anomalies are observed. These anomalies extend westward from central Mongolia but are bounded to the east by a high-resistivity anomaly whose location coincides with the Mogod fault zone. The aforementioned features highlight the control of major tectonic boundaries on the electrical resistivity distribution. An upper-mantle low-resistivity anomaly below the Khangai Dome, previously interpreted as a locally thinned lithosphere with an upwelling asthenosphere, is imaged not only beneath central Mongolia but also, to some extent, in the western region. The model also provides new information on the structure of major features across central-western Mongolia, such as the extensive Bulnay fault. Taken together, these new constraints on lithospheric properties and architecture advance our understanding of the mechanisms that shaped the region and its subsequent evolution.