Fig. 4

Resistivity model. The preferred 2-D resistivity model obtained with the MARE2DEM inversion algorithm (Key 2016) for magnetotelluric (MT) data at 39 sites along profile A–A′ (see map in Fig. 1). A combination of full MT sites (black triangles) and telluric-only sites (white triangles) was used. The base site used for inter-site transfer functions (with a local site) is indicated by the number above each site. Sites shown in Fig. 6 are marked. Distances are along the profile (approximately from north to south along longitude 100.5° E); latitudes of end sites are marked. The side panel shows a part of the modelling mesh used. Topography was included in the model and is shown in the upper panel with a vertical exaggeration (VE) of 15:1. The locations of nearby villages are displayed for reference (grey squares), as in Fig. 1: Bo Bogd soum, Ba Bayanlig soum, Gu Gurvantes soum. Gold square marks the location of Tsagaan Tsahir Uul (TTU) gold deposit. Names and locations of tectonic zones (grey bars at top) are from Kröner et al. (2010). The surface locations of prominent fault zones are indicated (black bars; Styron 2018; Walker et al. 2007). Fault extension in the subsurface (dashed grey lines) is speculated. Anomalous features in the upper crust appear coincident with known surface fault positions. They are believed to represent the boundaries of accreted terranes and their positions define distinct tectonic zones. Lower-crustal conductors may be in agreement with an allochthonous and relaminated lower crust. The seismically inferred crust–mantle boundary is at approximately 45 km (Petit et al. 2008). The proposed lithosphere–asthenosphere boundary (LAB) is indicated; it deepens towards the south