Intra-continental uplift and volcanism in the Hangai and Gobi-Altai Mountains in Mongolia

Insights from a multiscale magnetotelluric 3-D inversion

Abstract (2019)

Authors

Johannes Käufl ETH Zürich
Alexander V. Grayver ETH Zürich
M.J. Comeau University of Münster
Alexey Kuvshinov ETH Zürich
Michael Becken University of Münster
Jochen Kamm University of Münster
Erdenechimeg Batmagnai Mongolian Academy of Sciences
Sodnomsambuu Demberel Mongolian Academy of Sciences
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Published Date

2019

Language

English

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Abstract

Central Mongolia is a prominent region of intra-plate volcanism and deformation. To study these processes, many of which are poorly understood, magnetotelluric data was collected in the Hangai and Gobi-Altai region in central Mongolia. The geologic history of this region exhibits features over a wide range of spatial scales, which are coupled through a variety of geodynamic processes. Three-dimensional imaging using magnetotellurics can resolve the distribution of electrical resistivity within the Earth at scales ranging from tens of metres to hundreds of kilometres. However, designing a survey which can probe various scales and running subsequent three-dimensional inversions requires that multiple constraints imposed by the data acquisition cost, logistical efforts and computational complexity are satisfied.

We present an approach to survey design, data acquisition, and inversion that aims to bridge various spatial scales while keeping the required field work and computational costs feasible. This approach was applied to obtain the first 3-D multi-scale resistivity model of the Hangai and Gobi-Altai mountains. Magnetotelluric transfer functions were estimated for a 650 x 400 km2 grid, which included measurements on an array with regular 50 x 50 km2 spacing and along several profiles with a denser 5-15 km spacing for higher crustal resolution. A 3-D finite element forward modelling and inversion code was used in a four stage inversion process to obtain a resistivity model.

The final model reveals a complex resistivity structure and fits the observed data well across all periods and site locations. It resolves shallow structures in the upper crust, linked to surface observables (faults, volcanic provinces, hot springs), together with anomalous lithospheric conductors as well as a large-scale asthenospheric upwelling. This model provides crucial information to constrain numerical modelling of geodynamic processes related to the formation of the Hangai Mountains, as well as intra-continental deformation and volcanism.