Deformation in the continental interior, far from tectonic plate boundaries, is not fully understood. Due to its location, Mongolia is a prime natural laboratory for studying effects such as intracontinental deformation and intraplate volcanism. A previous regional magnetotelluric (MT) study, including three (2016-2018) field campaigns, identified a localized asthenospheric upwelling with a correspondingly thin lithosphere underneath the Hangai Dome (Central Mongolia). Compared with Central Mongolia, Eastern Mongolia is less studied with geophysical methods; consequently, its underlying lithospheric and asthenospheric properties are less constrained. At the same time, this region is of economic and scientific interest, as it hosts several mineral zones and relevant geological features, such as the Mongolia-Okhotsk suture zone. Furthermore, it is unknown to what extent the identified electrical conductivity anomalies in Central Mongolia extend to the east and how the crust and mantle differ in this region.This work presents the first results of a new MT field study covering Central-Eastern Mongolia. 64 broadband MT stations were deployed between 2020 and 2022 along five profiles east of the Hangai. The data were processed using a two-step multi-taper processing approach, simultaneously improving the quality at short and long periods, providing credible MT responses up to 2048 seconds. The previously acquired and new data were jointly inverted regarding 3-D conductivity variations. Furthermore, data from an 880 km long 2-D profile extending from the Selenga Basin to Gobi Desert were inverted independently. This study is part of a broader project aiming to constrain the electrical conductivity of entire Mongolia.@en

There are indications that some long-dormant or seemingly inactive volcanoes may have potentially active magma storage systems. One such system is Ciomadul volcano, which is located at the south-eastern terminus of the Carpathian volcanic chain (Romania). With the last eruption occurring at ~30 ka, this is the youngest volcano in eastern-central Europe. Understanding the nature and structure of the magma plumbing system is crucial to elucidating the evolution of the volcano and to assessing its hazard potential. This includes the depth, size, and geometry of the magma storage region, the amount and composition of the melt present, and the link between mantle and crustal processes. Ciomadul is situated in a geodynamically active region about 50 km from the Vrancea zone, where deep earthquakes are frequent. These earthquakes may represent the descent of a dense lithospheric slab beneath a continental collision zone and this may imply an asthenospheric upwelling due to return flow of mantle material. To the north-west of Ciomadul lies a chain of older volcanic complexes, the Călimani–Gurghiu-Harghita volcanic complex; about 40 km west of Ciomadul towards the Transylvanian Basin, a monogenetic basaltic volcanic region was developed at 1.2–0.5 Ma (Perşani volcanic field). Seismic tomography has revealed low-velocity columns through the lithosphere beneath both Ciomadul and Perşani. However, high-resolution images of the complex geometry of the system are lacking. We report here on a 3-D electrical resistivity model of the region that was generated from 41 magnetotelluric measurements acquired in 2022 that form a 75 km by 75 km array. The data typically had reliable periods from 128 Hz to 4,100+ s. Choosing appropriate locations for measurement was critical, away from sources of cultural electromagnetic noise that can contaminate the signals, as was careful data processing, including applying data pre-selection schemes and manual time windows in addition to standard approaches using robust statistics. Phase tensor analysis suggests that the data are 3-D at all scales. The 3-D electrical resistivity model reveals conductive anomalies (<10 ohm-m) in the subvolcanic crust. These are interpreted as melt-bearing magma reservoirs distributed in the mid-lower crust (depths of ~10–25 km) and a quasi-vertical conduit extending to the near surface. The crustal reservoir is oriented north-south, has its western margin beneath the surface vent of Ciomadul, and extends ~20 km eastward. These results are consistent with the quantitative petrological models placing the upper melt-bearing silicic crystal mush reservoir at a depth of 5–20 km beneath Ciomadul, and a magma-generation area in the asthenosphere (85–105 km depth). In contrast, no strong conductive anomaly is observed in the crust below Perşani, which fits the magma evolution model, i.e. small batches of mantle-derived magmas ascend rapidly through the crustal column. Our results suggest that Ciomadul, a seemingly inactive volcano, is still underlain by a melt-bearing magma body and therefore can be regarded as having potential for reactivation and further volcanic eruptions.@en