Crust-mantle interactions beneath the Hangai Mountains in western Mongolia: Insights from 3D magnetotelluric studies and 4D thermo-mechanical modelling

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The dome-shaped Hangai Mountain range in western Mongolia is an ideal natural laboratory for studying on-going and past intra-continental orogenic and magmatic processes resulting from crust-mantle interactions in space and time. While such intra-continental uplift and subsidence have long been recognized as an important part of continental tectonics, their origin remains enigmatic. The explanations are diverse and controversial and include uplift above a hot upwelling mantle, small-scale asthenospheric upwelling, magmatic underplating, crustal delamination and lower crustal flow. Thermo-mechanical modelling, when constrained by geophysical and geological data and models, can nowadays simulate realistic tectonic processes and test for different geodynamic hypotheses. While past and on-going geophysical studies have focused on gravity and seismology, magnetotelluric (MT) data are missing from the Hangai. MT data are particularly important, however, as these are the sole means of estimating crustal and upper mantle electrical conductivity, which is very sensitive to fluids and partial melt. Hydrous phases and melt, on the other hand, provide critical parameters for calibrating thermo-mechanical models. In this project, we propose to image crustal and upper mantle electrical conductivity beneath Hangai Mountains using 3D MT and to derive constraints for 4D high-resolution thermo-mechanical modelling studies. We expect to derive estimates on fluid/melt volumes and to identify regions of rheological weakness from the MT data, if present. The study aims to understand the processes responsible for developing dynamic topography in the Hangai Mountains and to place them within the larger framework of crust-mantle interactions and dynamic topography. The key components of the project are to 1) acquire, process, and invert MT data in western Mongolia in terms of 3D conductivity models; 2) to guide 4D thermo-mechanical modelling with constraints that derive from laboratory-based electrical conductivity models; 3) to perform 4D thermo-mechanical modelling. The proposed project is a collaboration between ETH Zurich (ETHZ, Switzerland) and the University of Münster (UoM; Germany) in the framework of the joint German-Austrian-Swiss (DACH) program and will be carried out in cooperation with the Research Center of Astronomy and Geophysics (RCAG) of the Mongolian Academy of Sciences. The project partners combine expertise in the fields of MT data acquisition, MT data processing, MT forward and inverse modelling, and geophysically-constrained 4D forward thermo-mechanical modelling.The main expected outputs from the project are 1) the first 3D geo-electrical model beneath the Hangai dome in Mongolia and 2) a geomorphological-thermo-mechanical model of intra-continental lithospheric deformation, magmatic activity, and evolution of dynamic topography that is consistent with the geophysical and geological observations.