The Har-Us-Nuur fault corresponds to one of the longest (>500 km) strike-slip fault in Mongolian Altai. Despite the fault clearly affects Quaternary deposits, no major instrumental or historical earthquake is associated to it and only a few morphotectonic and paleoseismological analyses have been carried out to date. In this paper, we describe a new surface rupture in the southern section of the Har-Us-Nuur fault along which we study in detail a 20 km long section of it. A morphotectonic analysis yielded a minimum slip rate of 0.32 ± 0.04 mm.yr¯¹, while paleosismological investigations suggest a mean recurrence interval of about 8.1 ± 3.4 kyr from the characterization of three surface rupturing events that occurred during the past 23 kyr. Combining this interval with a 5 - 6 m displacement estimated for the last seismic event, and assuming it corresponds to a characteristic slip and recurrence interval, yields a slip rate of 0.62 ± 0.27 mm.yr¯¹. These preliminary results suggest that the Har-Us-Nuur fault slip rate is inframillimetric and therefore lower than previous published estimates. They also suggest that the fault is able of producing major earthquakes (Mw ≥7.5) separated by very long period of quiescence.

We are investigating the lithospheric properties and lithospheric architecture beneath Mongolia with three-dimensional models of the electrical resistivity generated from magnetotelluric measurements. In addition, thermo-mechanical numerical modelling, with geophysically-guided constraints, is being used to provide valuable insights by testing the mechanical viability of different hypotheses for the temporal evolution and dynamic processes within this region. Mongolia is located between the relatively stable Siberian craton and the extensional regime near the Baikal rift zone to the north and to the south the North China and Tarim cratons that have a northward-directed compressional regime. Due to its location, it is an excellent region to study intracontinental deformation. Furthermore, enigmatic continental intraplate basaltic volcanism of the Cenozoic age exists across Mongolia. In addition, this region contains economically important mineral zones (copper and gold), with the origin and evolution of the mineral systems linked to the whole-lithosphere architecture, crust-mantle interactions, and mantle convection dynamics. Magnetotelluric data has been collected across Western, Central, and Eastern Mongolia. Three field campaigns in 2016, 2017, and 2018 collected more than 328 sites on an array (50 km spacing) and along three dense profiles (3-15 km spacing) that focused on the Hangai Dome (plateau) and Gobi-Altai (Arkhangai, Bayankhongor) over an area of approximately 800 km (north-south) by 400 km (east-west). Between 2020 and 2022, the array was extended to the east with 77 sites collected across central-east Mongolia (Bulgan, Selenge, Tuv, Uvurkhangai, Dundgovi; 400 by 200 km), including 34 sites along an 810 km long north-south profile crossing the Mongol-Okhotsk suture zone. In late 2022, 79 measurements were acquired in northern Mongolia across the Hovsgol region and Darhad (200 by 200 km) with an array and several profiles, which connect to data west of Lake Baikal. In early 2023, 38 sites were collected in central-east Mongolia (Umnugovi; 200 by 200 km), completing the eastern array. Later in 2023, a major field campaign was launched that successfully collected 150 measurements in western Mongolia (Zavkhan, Uvs, Govi-Altai, Khovd) over an area of approximately 500 by 400 km. This included an array (50 km spacing) and three dense profiles (5-10 km spacing). This gives approximately 700 magnetotelluric measurements collected over a total area of approximately 1000 km (north-south) by more than 1150 km (east-west). This is a large area that approaches the scope of several other regional and national magnetotelluric survey programs. What’s more, this dataset fills an important gap between the existing magnetotelluric data across China and the Tibetan Plateau with several profiles across the Siberian Craton, in principle completing a remarkable transect of 4000 km across a variety of tectonic domains. In this presentation, we will report on the new measurements. They will be integrated into the previously collected dataset, and new models will be generated that incorporate all data. We will also present new models of western, central and eastern Mongolia that provide insights on the properties, structure, and evolution of the Hangai Dome, the Mongol-Okhotsk suture and the Central Asian Orogenic Belt.

Abstract. A first block modeling study of the Mongolian Altay is presented, based on a new GNSS dataset acquired across the range with an innovative setup. Our results show that approximately 4–6 mm.yr-1 of dextral strike-slip motion is accommodated across the ~400 km-wide Altay deformation zone, consistent with previous geodetic estimates. Compared to the more scattered and heterogeneous slip rate estimates from morphotectonic studies, our results provide improved constraints on slip rates along the main Altay faults. Combining knowledge about fault activity across Altay with our results we also discuss the potential role of other unmodeled intra-block structures in accommodating deformation in the Altay and its periphery. This also leads us to question the highest previously reported slip rates—particularly along the Har-Us-Nuur and Fu-Yun faults.

Active tectonics of the northern Central Mongolia is studied between two largest W–E-trending left lateral fault zones – the Khangai Fault and the Tunka-Mondy zone. These strike-slip zones are parts of a single ensemble of active faults in the Mongol-Baikal region, formed under conditions of the maximum northeastern compression and the maximum northwestern extension. Between them, the ENE-trending Erzin-Agardag and Tsetserleg faults with dominant left lateral component of movements extend. A raw of the N-trending graben-shaped basins (Busiyngol, Darkhat, and Hubhugul) are situated between the eastern end of the Erzin-Agardag strike-slip fault and the western part of the Tunka-Mondy strike-slip zone. The basins form a zone of left lateral deformation, which is kinematically similar with the strike-slip faults continuing it. In contrast to the largest boundary strike-slip faults, this structural paragenesis was formed under conditions of N–S-trending relative compression and W–E-trending extension. A change in the orientation of the axes of the principal normal stress may be caused by the rotation of the block between the boundary faults. The area of graben-shaped basins is located above the uplift of the roof of a vast volume of low-velocity mantle, which we identify as the Khangai plume. Above this rise, the lithospheric mantle is reduced, and the remaining part of the lithosphere is heated and softened. The large active strike-slip faults are located above areas of lowering of the low-velocity mantle roof. Our trenching of the active faults showed that strong earthquakes repeated in the area of graben-shaped basins more often than in the large strike-slip zones, but were characterized by lower magnitudes.

The Mongol-Okhotsk suture and the Adaatsag ophiolite belt are associated with the closure of the Mongol-Okhotsk paleo-ocean and are located within the Central Asian Orogenic Belt (CAOB) and Mongolia. The suture zone is flanked by volcanic-plutonic belts that host significant metallogenic zones, containing deposits of copper and gold. The tectonic evolution of this region is not fully understood and the lithospheric structure has been poorly studied. We analyze magnetotelluric data and generate a model of the electrical resistivity distribution across this region. Whereas the northern segment has a sharp transition from a high-resistivity upper crust to a low-resistivity lower crust, as observed beneath the Hangai Dome, the southern segment does not show this transition. A wide, low-resistivity zone (1-100 Omega m) imaged in the crust and lithospheric mantle is coincident with the Mongol-Okhotsk suture and ophiolite, revealing a clear and significant lithospheric-scale feature. Across the profile, numerous narrow, vertically oriented, low-resistivity features (1-100 Omega m) are spatially associated remarkably well with the proposed boundaries of tectonic domains. These results confirm ideas about the development of the CAOB. Some of these low-resistivity features are beneath the surface locations of large mineral zones, and likely represent fossil fluid pathways. We show congruent seismic velocity models for comparison and the results show a large-scale low-velocity anomaly (decrease of 2%-3%) that correlates with the location of the low-resistivity anomaly below the Mongol-Okhotsk suture. The geophysical results, combined with geological and geochemical data, provide insights into the structure of this region and help shed light on unanswered questions. When the ancient Mongol-Okhotsk ocean closed, due to subduction from tectonic re-arrangement, it left the Mongol-Okhotsk suture zone and the Adaatsag ophiolite as a trace of its location. Similarly, other tectonic boundaries are hypothesized to exist from terrane accretion across the Central Asian Orogenic Belt (CAOB) and Central and Southern Mongolia, which is located between the Siberian and North China cratons. This region is also rich in economically significant copper and gold deposits. The tectonic evolution of this region and especially the lithospheric structure is not fully understood and has been poorly studied. We analyze magnetotelluric data and generate a model of the electrical resistivity distribution. Additionally, we show models of the seismic velocity for comparison. Examining multiple complementary geophysical models helps to reduce interpretation uncertainty. Anomalies are observed in both models (e.g., low resistivity and low velocity). The suture zone is proven to be a strong lithospheric-scale boundary. The proposed boundaries of tectonic domains are also imaged, confirming ideas about the development of the CAOB, and solving some controversies. Lithospheric-scale, wide, low-resistivity zone revealed below the ophiolite belt associated with the closure of the Mongol-Okhotsk ocean Vertical, narrow low-resistivity features aligned with proposed tectonic boundaries and locations of large mineral zones (copper and gold) The northern part of central Mongolia has a sharp mid-crustal transition from high to low resistivity, whereas the southern part does not

>In the framework of a mineral system approach, a combination of components is required to develop a mineral system. This includes the whole-lithosphere architecture, which controls the transport of ore-forming fluids, and favorable tectonic and geodynamic processes, occurring at various spatial and temporal scales, that influence the genesis and evolution of ore-forming fluids(Huston et al., 2016; Groves et al., 2018; Davies et al., 2020). Knowledge of the deep structural framework can advance the understanding of the development of a mineral system and the emplacement of mineral deposits. Deep geophysical exploration carried out with this aim is increasingly important for targeting new ore deposits in unexplored and underexplored regions(Dentith et al., 2018; Dentith, 2019).

A radially anisotropic shear wave model in the central Eurasian and Mongolian regions is constructed using multi-mode phase speeds of Love and Rayleigh waves. Our dataset includes seismic waveforms of over 2151 teleseismic events (Mw$>$5.8) from 2009 to 2021, recorded at permanent and temporary stations in and around Mongolia. At first, we performed fully nonlinear waveform fitting for individual seismograms to extract the multi-mode phase speeds of Love and Rayleigh waves. Then, we retrieved multi-mode phase speed maps incorporating finite-frequency effects. Finally, localized multi-mode dispersion curves derived from the phase speed maps were used to construct local anisotropic 1-D S-wave profiles, forming a 3-D shear wave model. Our new model exhibits significant lateral variations of S wave speeds at 70–100 km depth beneath Mongolia, i.e., slow anomalies in the tectonically active western Mongolia and fast anomalies in stable eastern Mongolia. The radial anisotropy model shows a faster SH wave speed than SV in almost the entire Mongolian lithosphere above 100 km depth, except for the northern Altay Mountains region. The Hangay Dome region is characterized by significantly slower velocities, indicating the asthenospheric upwelling that causes the uplifting of this region. This study reveals distinct lateral variations of S wave speeds near the boundary between the Eurasian and Amurian plates, characterized by the prominent fast anomaly of the dipping lithosphere in the western margin of the Amurian plate.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070206

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070206

The study area is located in the Ulaanbaatar basin and is characterized by complicated environmental conditions determined by the peculiarities of an extremely continental climate with high rainfall intensity, a structural–tectonic pattern, the geological structure of the Ulaanbaatar intermountain depression, high seismic activity reaching 8 points, and the occurrence of catastrophic flash floods. In the conditions of rapid urban expansion, the high population density and housing development of Ulaanbaatar, and the implementation of large investment projects, it is an urgent task to assess the exogeodynamic hazard of the Ulaanbaatar catchment basin and develop the concept of geoecological safety of the territory. These methods and approaches consist of combining a complex of methods of engineering geology and geomorphology: monitoring the dynamics of exogenous processes; environmental assessment; the analysis of development factors (climatic, geomorphologic, tectonic, and lithological) and interaction of processes; laboratory methods of analyzing the composition, structure, and properties of soils; a detailed morphometric analysis of catchment areas; and the application of the basin approach. Based on the analysis of topographic maps on a scale of 1 : 50 000 and of digital relief models in GIS programs, the parameters of the drainage network of the catchment areas and of energy and basin geometry were calculated and reflected on map layers, and specialized maps were compiled. A detailed assessment of erosion-prone soils (composition, structure, and specific properties) revealed a moderate resistance of sediments to geodynamic impacts. As a result, maps of flood hazard of catchments under different rainfalls—short intensive heavy rainfalls and long-term rains—were compiled. The elaborated concept of geoecological safety of territories includes successive stages of works aimed at (a) identifying the exogeodynamic hazard, (b) the organization and implementation of monitoring works, (c) assessing geoecological safety with respect to hazardous exogenous geological processes, and (d) the development of recommendations for further use and specification of information.

The Baikal Natural Territory (BNT) and Khuvsgul region have similar environmental problems. It is relevant to carry out integrated scientific studies and monitor the state of the components of the natural environment in these areas. This paper presents the results of a number of joint Russian–Mongolian projects aimed at studying and developing new methods and technologies for integrated environmental monitoring and prediction. A digital platform has been created to support scientific research and environmental monitoring. This platform makes it possible to collect, store, process, and analyze large arrays of heterogeneous spatiotemporal data and predict environmental situations using a set of mathematical and information models, services, and machine learning methods. The authors have also developed methods and web services for environmental monitoring based on the processing of Earth remote sensing (RS) data. A technology for classifying multispectral Sentinel-2 satellite images has been created that makes it possible to distinguish 12 classes of the land cover using artificial intelligence methods. A service for monitoring the state of the atmosphere over large areas has been created based on the processing of Sentinel-5P satellite data. This service makes it possible to display the concentrations of SO 2 , NO 2 , CO, CH 4 , H 2 O, O 3 , formaldehydes, and aerosols in the air.

Comparative hydrogeochemical studies of groundwater in the Ulaanbaatar reservoir and those in the coast of Lake Baikal show significant difference between hydrogeodynamic processes of these areas, the earlier generation of U-isotopic and Si–Na–Li-temperature anomalies in the Ulaanbaatar groundwater reservoir and the later in those of the Baikal coast.

New and generalized published data on the structure, age, and formation stages of deposits of the mantle and alluvial genetic complexes of the first terrace of rivers in the Selenga drainage basin are presented. The sections of the terrace of the Bryanka River in the Bryansk Depression, the Arshan River in the Khilok–Chikoi Depression, and the Shivert-Gol River in the Boro-Gol River basin in Mongolia are described. Information on the terrace structure and on the composition and absolute (radiocarbon) age of deposits is obtained. The first terrace 4–9 (15) m high above low water level is distinguished in the Selenga drainage basin. Large differences in the structure and composition of the terrace deposits depend on the morphology of the river valleys, water discharges, and the structural and tectonic conditions of the river basins. It has been established that the accumulation of sediments of the first river terrace in the Selenga basin began at the end of the Late Pleistocene. The channel, floodplain, and oxbow alluvium facies are distinguished. Channel alluvium was accumulated 30–15 cal kyr BP, and the accumulation of floodplain alluvium occurred during the Late Glacial and Early Holocene (15–8 cal kyr BP). The alluvium is overlain by Holocene sediments of the mantle genetic complex of different composition, genesis, and age reaching 3.5 m in thickness. It has been revealed that the first terrace of rivers in the Selenga drainage basin was formed in the Early Holocene (11.3–8 cal kyr BP) as a result of incising of the rivers during high floods. The chronological stages of sedimentation and soil formation have been identified. There was a long stage of soil formation 7–2 (0) cal kyr BP after the alluvium accumulation stop.

The Khangai plume is located beneath Central and Eastern Mongolia and corresponds to the mantle volume with significantly reduced longitudinal wave (P) velocities. The plume was identified as a result of the analysis of the MITP08 volumetric model of variations in P wave velocities, expressed as deviations of these velocities from the mean values for the corresponding depths in percent. Above the plume, the lithospheric mantle is thinned to ~50 km. Particularly low velocities (up to –6%) were found in the sublithospheric mantle down to a depth of 400 km. The main body of the plume is located under the Khangai Highland and spreads north to the edge of the Siberian Platform. The Khentei branch of the plume is identified southeast of the Khentei Highlands. It is connected to the main body of the plume at depths of 800–1000 km. Branches of the plume and its Khentei branch spread to Transbaikalia. The size of the plume decreases with depth, and its deepest part (1250–1300 km) is located under the southern part of the Khangai Highland. On the Earth’s surface, the main body of the Khangai plume corresponds to a Cenozoic uplift up to 3500–4000 m high in the south of the Khangai Highland. From the southeast, the territory of the Khangai plume and its Khentei branch is limited by the Late Cenozoic troughs stretching along the southeastern border of Mongolia. On other sides, the Khangai uplift is limited by a C-shaped belt of depressions, consisting of the southeastern part of the Baikal rift zone, the Tunka and Tuva basins in the north, the Ubsunur Basin and the Great Lakes Basin in the west and the Valley of Lakes in the south. The depressions are filled with lacustrine and fluvial sediments from the Late Oligocene to the Pliocene. In the Quaternary, the Southern and Central basins of Baikal, formed no later than the Early Paleogene, became part of the Baikal rift, and other depressions were involved in the general uplift of the region. The structural paragenesis of the Khangai uplift and surrounding basins is due to the impact of the Khangai plume. Above the plume with its Khentei and Transbaikalian branches, the Cenozoic basaltic volcanism of the plume type occurred, in some places inheriting Cretaceous volcanic manifestations. Plume structural paragenesis is combined with structural paragenesis, derived from the interaction of plates and lithosphere blocks, which is expressed by active faults, but developed synchronously with plume paragenesis. The kinematics of active faults shows that the western and central parts of the region develop under conditions of transpression, and the northeastern part ‒ under conditions of extension and transtension. The Khangai plume is connected at depth with the Tibetan plume, located under the central and eastern parts of Tibet north of the Lhasa block. The Tibetan plume rises from depths of 1400–1600 km and is accompanied by thinning of the lithosphere and rise of the earth’s surface. The Khangai and Tibetan plumes represent a special category of plumes that rise from the upper part of the lower mantle and this differs from the upper mantle plumes and the African and Pacific superplumes, rising from the core-mantle boundary. A connection between the Khangai and Tibet plumes with branches of superplumes is possible, but their independent origin is also admitted.

topographic pattern and elevated surface observed. Additionally, it at the compatible with the available petrological and likely mantle decompression A may have is determined be a physically plausible mechanism, with the available evidence, and a potential explanation for the intraplate surface uplift, and the intraplate volcanism.

Water flows with significant flow rate feature a high destructive force and can lead to catastrophic consequences. Fluvial processes caused by uneven distribution of rain precipitation over the area pose risks to the developed inland foothill territories. The purpose of this study is to carry out a quantitative morphometric analysis of the territory in order to identify the formation features of flood flows. The analysis and ranking of catchment basins are performed using a basin approach. On the basis of SRTM images and the use of stock cartographic material in the GIS program the authors have built specialized electronic maps that allow to obtain quantitative parameters reflecting the morphometry of the basins under analysis including basin geometry, drainage network and terrain relief. On example of the Ulaanbaatar agglomeration territory it is shown how initial morphometric parameters of basins and watercourses (length, width, area, perimeter, erosion dissection, drainage network density, terrain relief coefficient, Melton coefficient, etc.) form the features of flood flow. For developed territories, the initial data on the catchment basin morphometry constitute the basis for compilation of specialized maps to be used in planning and construction. The combination of morphometric indicators on the territory of the Ulaanbaatar agglomeration indicates that there is possibility of large flood formation and development of dangerous mudstone flows in some catchment basins.

both the genesis of minerals and the locations of mineral emplacement; thus knowledge of the deep structural framework of the lithosphere can advance understanding of the development and evolution of mineral systems (e.g., Huston et al., 2016; Groves et al., 2018; Davies et al., 2020). Transient tectonic and geodynamic processes — occurring at various spatial and temporal scales — control the structure of the lithosphere. In turn, this structure influences the transportation of fluids (including oreforming fluids) through the crust, largely by controlling permeability (e.g., Huston et al., 2016). These concepts are widely seen as the key to gaining an understanding of deep ore genesis, with a focus on the critical processes of ore-forming fluid generation and transportation as well as concentration and preservation (e.g., Davies et al., 2020, and references therein). Moreover, deep (geophysical) exploration studies carried out with these concepts in mind may be crucially important for targeting new ore deposits in unexplored and underexplored regions (e.g., Dentith et al., 2018, and references therein; Dentith, 2019). We analyze data from magnetotelluric (MT) measurements across southern Mongolia (data described in Becken et al., 2021a, b) and explore three dimensional (3-D) models of the electrical resistivity structure throughout the whole lithosphere, from the upper crust to the asthenosphere (see Comeau et al., 2021; see also Käufl et al., 2020). This region has notable occurrences of gold and copper mineralization over an extended area and is located near the edge of a micro-continental block. We interpret the geophysical results, with the help of available geological and geochemical data, with respect to the potential implications for fluid generation and transportation and discuss links to the surface expressions of known mineral deposits. Methods: Magnetotelluric exploration The MT method is a geophysical exploration technique that uses natural electromagnetic signals to image the subsurface electrical resistivity structure. MT data consists of natural electromagnetic fields measured at the Earth’s surface over a broad range of frequencies, with signals generated in the atmosphere and ionosphere. This allows the exploration of multiple spatial scales: short-period data are sensitive to shallow structures and long-period data are sensitive to deep structures (e.g., Unsworth and Rondenay, 2012). MT data is particularly sensitive to the amount and composition of fluids, which tend to reduce electrical resistivity. This makes the technique well-suited to image the internal structure of fault zones, magmatic systems, and deep lithospheric structures (e.g., Becken et al., 2008, 2011; Comeau et al., 2015, 2018, 2020; Käufl et al., 2020). In addition, numerous studies have shown that the MT exploration technique is capable of characterizing the pathways of past fluids and the traces of mineral alteration (e.g., Hübert et al., 2015; Wise and Thiel, 2019). Recent work has linked the formation of mineral ore deposits with deep electrical signatures — including the work of Heinson et al. (2018) on the Olympic Dam deposit, Australia; Comeau et al. (2021) on mineralization in the Bayankhongor belt, Mongolia; and Yin et al. (2021) on ore zones in Nanling, China, amongst others. The multi -scale nature of the MT exploration technique enables imaging of the fluid source region in the deepest parts of the lithosphere or crust as well as fluid pathways or conduits in the upper part of the crust. Results and discussion: Origin and transportation of ore-forming fluids Electrical resistivity models reveal multiple conductive (low resistivity) features of interest at different spatial scales and depths throughout the lithosphere, including: a) expansive, deep-seated conductive zones, attributed to the fluid source region and to thermal anomalies; b) conductive anomalies within the resistive upper crust, which give evidence for the ancient pathways of oreInvestigating the Whole-lithosphere Structure of a Mineral System — Pathways and Source of Ore-forming Fluids Imaged with Magnetotelluric Modeling