Baikal Rift Research Articles

FIRST LA-ICP-MS APATITE FISSION-TRACK AGES FROM THE SIBERIAN PLATFORM BASEMENT (NEPSKO-BOTUOBINSKAYA ANTECLISE)

We present the first results of LA-ICP-MS apatite fission-track dating (AFT) from nine core samples from wells, that exposed the top of the crystalline basement of the Siberian platform within the Nepsko-Botuobinskaya anteclise on the ~2 km depth. Obtained AFT ages belong to three clusters with mean values of 200, 140, and 60 Ma. A thermal event of ~200 Ma is widespread throughout almost the entire Siberian platform and reflects the stage of its Early Jurassic uplift. Reset of the fission-track geochronometer in apatite ~140 Ma correlates with tectono-thermal event marking the final stage of the Mongol-Okhotsk fold belt collision. The youngest AFT ages of ~60 Ma, on the one hand, may reflect the early (crypto) stage of the Baikal rifting, and, on the other hand, be a consequence of the high content of uranium in apatite.

Numerical Analytical Methods for Calculating Wave Fields and Reconstructing the Velocity Characteristics of Inhomogeneous Elastic Media in the Baikal Rift Zone

Numerical Analytical Methods for Calculating Wave Fields and Reconstructing the Velocity Characteristics of Inhomogeneous Elastic Media in the Baikal Rift Zone

3D seismic tomography models of the Baikal Rift zone and surrounding areas based on regional seismological data

3D seismic tomography models of the Baikal Rift zone and surrounding areas based on regional seismological data

Sources of Late Cenozoic Deposits from the Aeolian “Sands” Massif in the Chara Basin of the Baikal Rift Zone: First Results of U–Th–Pb (LA-ICP-MS)-Geochronological Study of Detrital Zircon

Sources of Late Cenozoic Deposits from the Aeolian “Sands” Massif in the Chara Basin of the Baikal Rift Zone: First Results of U–Th–Pb (LA-ICP-MS)-Geochronological Study of Detrital Zircon

SOURCES OF THE LATE CENOZOIC DEPOSITS FROM THE AEOLIAN “SANDS” MASSIF IN THE CHARA BASIN OF THE BAIKAL RIFT ZONE: FIRST RESULTS OF U–TH–PB (LA-ICP-MS) GEOCHRONOLOGICAL STUDY OF DETRITAL ZIRCON

The results of U–Th–Pb (LA-ICP-MS) geochronological studies of detrital zircon (fraction more than 50 µm) from the Late Cenozoic deposits of the large aeolian “Sands” massif of the Chara Basin of the eastern flank of the Baikal Rift Zone show that they are dominated by detrital zircon with ages of 263–265 and 1861–1864 Ma. Archean ages have been obtained only for individual zircon grains. Quite possibly, this is due to the fact that zircon of this age is present in “small” fractions, the study of which is not possible due to the technological features of the method of geochronological studies used. Based on the geological situation, only granites of the Kodar complex can be considered as the only source of detrital zircon of the Early Proterozoic age. The source of detrital zircon with an age of 263–265 Ma remains a mystery. Granitoids of this age are not known on the territory of the Aldan Shield. They are widespread in its western frame.

Structure and Dynamics of Lithosphere and Asthenosphere in Asia: A Seismological Perspective

AbstractKnowledge of lithospheric structure is essential for understanding the impact of continental collision and oceanic subduction on surface tectonic configurations. Full‐waveform tomographic images reveal lateral heterogeneities and anisotropy of the lithosphere and asthenosphere in Asia. Estimating lithospheric thickness from seismic velocity reductions at depth exhibits large variations underneath different tectonic units. The thickest cratonic roots are present beneath the Sichuan, Ordos, and Tarim basins and central India. Radial anisotropy signatures of 11 representative tectonic provinces uncover the different nature and geodynamic processes of their respective past and present deformation. The large‐scale continental lithospheric deformation is characterized by low‐velocity anomalies from the Himalayan Orogen to the Baikal rift zone in central Asia, coupled with the post‐collision thickening of the crust. The horizontal low‐velocity layer of ∼100–300 km depth extent below the lithosphere points toward the existence of the asthenosphere beneath East and Southeast Asia, with heterogeneous anisotropy indicative of channel flows.

The North Asian Genus Kolhymamnicola Starobogatov and Budnikova 1976 (Gastropoda: Amnicolidae), Its Extended Diagnosis, Distribution, and Taxonomic Relationships

The taxonomic position and phylogenetic affinities of the endemic North Asian genus Kolhymamnicola Starobogatov and Budnikova, 1976 (Gastropoda: Amnicolidae) remain unknown. To resolve this, we studied key morpho-anatomical characteristics of Kolhymamnicola snails and performed a molecular phylogenetic analysis based on sequences of COI mtDNA, 16S rRNA, and 18S rRNA genes. In terms of protoconch microsculpture, operculum, radular teeth, and gill complex morphology, Kolhymamnicola snails do not differ significantly from the North American genera Amnicola Gould and Haldeman, 1840 and Taylorconcha Hershler et al., 1994, and the European genus Marstoniopsis van Regteren Altena 1936. The bifid penis found in Kolhymamnicola is similar to that in the genus Marstoniopsis. The female reproductive anatomy has some features shared by Kolhymamnicola and Taylorconcha (absence of bursa copulatrix, single seminal receptacle in rs2′ position, and ventral channel). The molecular analysis has revealed Taylorconcha as the closest relative to Kolhymamnicola; the COI-based genetic distance between them amounted to 0.113. We discuss the possible time of divergence of these two genera, as well as of European Marstoniopsis and the Baikal Lake endemic family Baicaliidae. The last common ancestor of these groups was widely distributed in Miocene–Pliocene in the Holarctic waterbodies. Recent Kolhymamnicola snails are distributed in Northern Asia, including lakes of the Baikal rift zone. We rank the Baicaliidae as a family rather than a subfamily of Amnicolidae based on their distinct, unique morpho-anatomical characteristics and highly supported separate position on the molecular tree. The tribe Erhaiini Davis and Kuo, 1985 is elevated to the rank of the family, with 3–4 recent genera included. The family Palaeobaicaliidae Sitnikova et Vinarski fam. nov. is established to embrace the Cretaceous North Asian gastropods conchologically similar to the recent Baicaliidae and Pyrgulidae.

3D model of the Selenga depression of the Baikal rift zone

The article presents the results of the interpretation of unique archival data of vertical electrical soundings obtained in the Selenga basin of the Baikal rift zone in the 50s of the last century by the detachment of the Baikal geophysical expedition of the PGO "Irkutskgeofizika", using modern computer technologies. The purpose of this work is to refine the geoelectric characteristics of the sections according to the measurement profiles, as well as the structure of such seismically active structures as the Delta and Fofanovsky faults, the Proval Bay, the Tvorogovo-Istok uplift using a 2–3D inversion program with visual data visualization.

Chemical Modification of Lherzolite Xenoliths Due to Interaction with Host Basanite Melt: Evidence from Tumusun Volcano, Baikal Rift Zone

To investigate the process and chemistry of mineral reaction zone formation, we conducted detailed petrographic observations and chemical analysis of rocks and minerals of spinel lherzolite xenoliths from basanites of Tumusun volcano (Baikal Rift Zone). The reaction zones gradually disappear from contact toward the center of the xenoliths. The influence of basanite melt on major and trace element composition of secondary minerals of reaction zones is notable only at a distance up to 100–200 μm from the contact. At a distance of 0.3–1.0 mm from the contact, the major and trace composition of secondary clinopyroxenes from the orthopyroxene reaction zone indicates their formation from a melt formed by dissolution of orthopyroxene and influenced by the element diffusion from basanite melt. Inside xenoliths, the secondary minerals have Mg# values equal to or higher than Mg# of primary minerals, and secondary clinopyroxenes inherit their depleted or enriched REE pattern from primary pyroxenes. The compositional variations in secondary clinopyroxenes testify melt heterogeneity. Clinopyroxene rims have slightly higher LILE and similar abundances of other trace elements compared to clinopyroxene cores. This is consistent with the model developed from experimental studies: due to the interaction with basanite, incongruent dissolution of orthopyroxene occurs to form a melt which circulates in lherzolite and leads to pyroxenes and spinel dissolution. Diffusion of elements from basanite results in lherzolite enrichment in K, Na, Rb, Ba, La, and Ce, which are incorporated in feldspars and clinopyroxene of reaction zones as well as in feldspar veinlets. Non-dissolved mineral cores are homogenous and similar in major and trace element composition to primary minerals without reaction rims.

Deep Velocity Structure and Seismicity of the Trans-Baikal Region (Along the Reference Geological and Geophysical Profile 1-SB)

The paper presents analysis of the seismicity and deep structure of the Trans-Baikal region in the section of the reference geophysical profile 1-SB. It was determined that the Earth’s crust and upper mantle has a complex heterogeneous structure. The thickness of the Earth’s crust varies from 40 km in the South-Eastern part of the profile and in the areas of intermountain depressions in the North-Western part, and up to 48 km in the areas of mountain ranges. The values of the boundary velocities along the M boundary also vary greatly, from higher values of 8.4‒8.5 km/s for P-waves and 4.9‒4.95 km/s for S-waves (especially in the South-Eastern part of the profile) to reduced values of 7.8‒8.0 km/s for P-waves and 4.6‒4.7 km/s for S-waves in the section of the Baikal rift zone in the North-Western part of the profile. A strong inhomogeneous structure of the medium in terms of elastic wave velocities, Vp/Vs velocity ratios, and the Poisson’s ratio is determined for the upper and the middle crust at depths of 8‒20 km. The authors determined that zones of increased seismicity are referred to blocks of the Earth’s crust with inhomogeneous velocity structure according to data of differently polarized P- and S-waves. The area of the Baikal rift zone, in the immediate vicinity of the largest Muya earthquake of 1957 with M = 7.6, is characterized by elevated inhomogeneity in the upper part of the Earth’s crust according to the elastic wave velocities and secondary parameters of the medium (Vp/Vs ratio, K* = = Vp/(γ – 1), where γ = Vp/Vs, Poisson’s ratio (σ)). A number of other inhomogeneous deep zones have also been identified in the profile based on anomalies of P- and S-waves velocities and secondary parameters of the medium, which correlate to varying degrees with seismically active sites according to long-term instrumental observations. The established unambiguous connection of large inhomogeneous zones of the upper crust of the Trans-Baikal region with the accumulation of stresses and their discharge in the form of strong earthquakes allows us to make a reasonable medium-term forecast of catastrophic events.

THREE-DIMENSIONAL VELOCITY STRUCTURE OF THE CRUST IN CENTRAL LAKE BAIKAL FROM LOCAL SEISMIC TOMOGRAPHY

This work deals with the importance of studying seismicity and deep structure of the Earth’s crust in the region of the Baikal rift zone. The study presents a three-dimensional velocity structure of the Earth’s crust in the central part of Lake Baikal, obtained from the results of tomographic inversion of the travel times of P- and S-waves from more than 800 seismic events. Synthetic tests provide substantiation for the resolution of the tomographic inversion algorithm. The seismic structure of the crust was obtained to a depth of 35 km and has a direct relationship with the geological structure. The three-dimensional distributions of seismic P- and S-wave velocity anomalies are in good agreement with each other.The sharp contrast between the anomalies may indicate a difference in the material composition of the basement of the Central Baikal basin. At a 15-km depth below the Selenga River delta, there is observed a strong low-velocity anomaly which confirms the presence of a thick sedimentary cover therein. In the basement (at depths of 20 km or greater), to the northeast of the intersection between the Delta fault and the Fofanov fault, there occurs a high-velocity anomaly elongated towards the Olkhon Island. This anomaly is probably related to a rigid block in the earth’s crust. The same depths, on the western side of the Baikal-Buguldeika fault, show a reduced Vp/Vs ratio: 1.56–1.65 versus 1.70–1.75 in the adjacent areas. This indicates another type of basement rock composition and the presence of consolidated matter there.Besides, there has been made a more accurate hypocenter determination for further comparison between seismic events and active fault structures. For the central part of Lake Baikal, the distribution of seismicity mainly corresponds to depths of 10–22 km. The situation is different below the Selenga Delta – the only area where seismicity is observed at depths greater than 22 km, – which can be attributed to complex fault interactions.The velocity anomalies discussed herein are confined to reliably identified active faults and correlate well with the distribution of seismicity and gas hydrate structures.

Impacts of Tectonic Subsidence on Basin Depth and Delta Lobe Building

AbstractChannel avulsions on river deltas are the primary means to distribute sediment and build land at the coastline. Many studies have detailed how avulsions generate delta lobes, whereby multiple lobes amalgamate to form a fan‐shaped deposit. These studies often assume a steady subsidence and uniform basin depth. In nature, however, lobe building is disrupted by variable subsidence, and progradation of lobes into basins with variable depth: conditions that are prevalent for tectonically active areas. Herein, we explore sediment dispersal and deposition patterns across scales using measurements of delta and basin morphology compiled from field surveys and remote sensing, collected over 150 years, from the Selenga Delta (Baikal Rift Zone), Russia. Tectonic subsidence events, associated with earthquakes on normal faults crossing the delta, displace portions of the topset several meters below mean lake level. This allogenic process increases regional river gradient and triggers lobe‐switching avulsions. The timescale for these episodes is shorter than the predicted autogenic lobe avulsion timescale. During quiescent periods between subsidence events, channel‐scale avulsions occur relatively frequently because of in‐channel sediment aggradation, dispersing sediment to regional lows of the delta. Avulsion settings for the Selenga Delta preserve discrete stratal packages that could contain predominately deep channels. Exploring the interplay between tectonic subsidence and sediment accumulation patterns will improve interpretations of stratigraphy from active margins and basin models.

Stochastic Simulation and Development of the Ground Motion Prediction Equation for the Baikal Rift Zone

Stochastic Simulation and Development of the Ground Motion Prediction Equation for the Baikal Rift Zone

Cenozoic sediments from the Selenga-Vitim Downwarp and Baikal Rift Zone spatially combined in the Uro section

Research subject. Cenozoic stratified sedimentary formations exposed by well 517 in the Uro area.Aim. To study a section of spatially combined deposits from the Selenga-Vitim Downwarp and Baikal Rift Zone.Methods. Lithological and stratigraphic analysis, lithogeochemical, paleontological studies.Results. Oligocene deposits of the Kularikta Formation from the Selenga-Vitim Downwarp found for the first time, unconformably overlain by deposits of the Baikal-type basins of the Baikal Rift Zone (Miocene-Lower Pliocene Tankhoi Formation, Upper Pliocene-Eopleistocene Anosov Formation, and Quaternary polyfacies stratum). Four palynocomplexes are characteristic of the section: PC I of the Early Oligocene shows mixed forests of spruce, pine, hemlock with an admixture of alder, birch, and broad-leaved deciduous trees with an insignificant participation of evergreens that existed in a warm temperate climate; PC II of the Late Oligocene reflects expansion of areas of coniferous vegetation in the transition to a moderate climate; PC III of the Early Miocene demonstrates mesophilic coniferous forests and a significant role of broad-leaved tree species in warmer and more humid climatic conditions; PC IV of the Late Miocene–Early Pliocene displays vegetation close to taiga with rare relics of coniferous and deciduous plants under conditions of increasing cooling with a decrease in total moisture supply. A lack of pollen grains in the transitional deposits from the Kularikta to the Tankhoi Formation of the late Oligocene–early Miocene corresponds to conditions of a paleoclimatic pessimum. A member of lacustrine sediments with diatoms was found in the Tankhoi Formation, 50 species of diatoms are identified, among which the planktonic species Alveolophora antiqua is absolutely dominant in a paleowater body of significant depths and a large volume of water mass.Conclusion. The Uro section combines the Oligocene deposits of the Selenga-Vitim Downwarp and Miocene-Quaternary deposits of the Baikal Rift Zone.

Измерение современных движений на станции «Талая» (юго-западная часть Байкальского рифта)

The rates of modern displacements are an important factor in the modern geodynamics of the Baikal rift system. Reflection of strong earthquakes in the experimental values of displacements is still to be discussed, as well as the question of modern vertical movements. According to the measurements of 1992–2022, performed by the methods of absolute gravimetry and space geodesy, the velocities of vertical and horizontal movements at the Talaya seismic station (Baikal Rift). The displacement rates were determined as 1.7 mm/year – 1.9 mm/year at the SEE relative to the Irkutsk point (Siberian platform). A set of methods was used to obtain the vertical velocity val-ues for different epochs, pre-, co- and post-period of Kultuk earthquake (2008, M = 6.3, 25 km to the epicenter). Subsidence rates vary from 1.1 mm/yr to 3.3 mm/yr. Possible signs of the preparation of Baikal earthquakes have been identified.

Первый опыт мониторинга косейсмических и асейсмических вариаций ОВП, рН и температуры подземных вод Култукского резервуара в режиме реального времени (Байкальская рифтовая система)

Automatic probes were installed in two wells in the area of Kultuk settlement to determine real-time variations of ORP, pH, and temperature in groundwater. The obtained data were interpreted and compared with seismic pulses on November 22-25 and December 16, 2023 in the central part of the Baikal Rift System.

Структура Растительного покрова Амутской котловины (Джергинский заповедник, Республика Бурятия)

Large-scale vegetation mapping makes it possible to assess the spatial structure of communities at the local level. The Amut Basin is one of the small intermountain basins of the Baikal rift zone. The basin was formed in a complex orographic junction of the Barguzinsky, Severo-Muysky, Yuzhno-Muysky and Ikatsky ridges. The basin is a part of the Dzherginsky Nature Reserve. It was organized to protect the natural complexes of the sources of the Barguzin River. Despite the simplicity of the vegetation structure, there is an interpenetration of elements of different phratries of formations — the Ural-Siberian, Angarid and Berengian. This indicates a complex history of the development of the vegetation cover of the territory. A large-scale geobotanical map makes it possible to create the basis for a balanced protection of the natural complexes of the reserve and contributes to identifying the local structure of the vegetation cover of the Baikal rift zone. Analysis of the resulting map shows the relative simplicity of the communities diversity in the basin. 12 groups of indigenous associations and 3 categories of derived communities have been identified. The main coenogenetic groups were not identified due to the insignificant participation of elements of the Ural-Siberian and Berengia phratries of formations. The dominant formations in the basin belong to the Angarid phratry. They are represented by Dahurian larch communities. The Berengian element of cenoses, Pinus pumila, dominates in limitedly widespread cenoses, but as an undergrowth it is found everywhere in larch forests. Pure dark coniferous forests of the Ural-Siberian phratry of cedar (Pinus sibirica) and fir (Abies sibirica) were not recorded on the territory of the basin; however, cedar undergrowth and individual cedar specimens are found regularly on the territory. Spot growth of an element of the South Siberian formations of the Ural-Siberian phratry — Caragana jubata — in coastal shrub and forest cenoses should be noted. The overall disturbance of the area’s vegetation cover is low. Traces of fires in the basin are sporadic, and burnt areas distribution is limited. Regeneration processes are actively taking place in burnt areas. The main role in the preservation of the natural complexes of the Amut Basin is played by the fact that the basin with adjacent territories is the part of the Dzherginsky Nature Reserve. The reserve was founded on the basis of a complex zakaznik (protected area) that existed here since 1974. The created map can serve as the basis for conducting monitoring observations of succession processes in the territory, identifying widespread and less widespread cenoses in the reserve, and also for zoning the territory for environmental purposes. Currently, it is planned to create a large-scale vegetation map for the entire territory of the Dzherginsky Nature Reserve.

Косейсмическая химическая гидрогеодинамика Култукского резервуара подземных вод: индикаторные роли Na/Li, 234U/238U и 234U

Within the framework of the complete seismogeodynamic cycle of the central part of the Baikal Rift System, in the series of hydrogeochemical data obtained in 2012–2022 at stations of the Kultuk polygon, variations of the thermophilic elements Na and Li and Na/Li ratios are traced in connection with changes in the 234U/238U activity ratios and 234U activity, reflecting the opening and closing of microcracks for circulating groundwaters. Coseismic chemical hydrogeodynamics of the Kultuk groundwater reservoir is considered in terms of temperature and extension–compression of the crust.

Трансформация геосистем Байкальской природной территории

The article presents the main provisions of the concept of transformation of geosystems of geodynamically active territories. The object of the study is the geosystems of the Baikal natural territory. The interaction of the Siberian Platform, the East Sayan Mountain region, the Baikal rift zone, the Angara-Vitim batholith influenced the formation of various conditions for the transformation of geosystems. Modern ideas about the influence of endogenous processes on the transformation of the lithosphere and climate are considered. The transformation of geosystems is understood as the restructuring of their structure due to transformative dynamics and evolution, which develop under the influence of the modification of material-energy flows and information connections. Examples of transformation of geosystems of the Baikal natural territory under the influence of endogenous heat and mantle matter, changes in information connections of components of geosystems and their subordination to geosystems of physical and geographical areas are given.

Разработка Листвянского, Бугульдейского и Ольхон-Приольхонского мониторинговых полигонов на Байкале: обзорное изучение микроэлементов и изотопов U в речных и подземных водах

The results of prospecting studies of trace elements and activity ratio 234U/238U (АR4/8) in surface waters and groundwaters from the Listvyanka, Buguldeyka, and Olkhon-Priolkhonye polygons of integrated monitoring, organized since 2020, are presented. At the Listvyanka polygon, wide interval of АR4/8 from 1.67 to 2.5 is obtained for groundwater in the Bolshie Koty village, at the Buguldeyka and Olkhon-Priolkhonye polygons that are located in the zone of the Primorsky fault – an interval of AR4/8 from 1.25 to 2.70. These values is general characteristic of large active faults of the central Baikal Rift Zone. Water from the Buguldeyka River differs in terms of both trace element compositions and AR4/8 values from those of its tributary Kurtun due to location of these rivers basins in rocks of the exposed basement of the Siberian Platform and its sedimentary cover, including evaporate carbonate sediments. On the Olkhon island, determined is groundwater that differs in elemental composition from the deep Baikal water.