A model of tectonothermal evolution of the Zagan metamorphic core complex (MCC) based on the new data from 40Ar/39Ar dating of amphibole, mica, and apatite fission-track dating is discussed. A relationship with the long-range impact of processes from the collision of the North China (Amurian–North China) block with the Siberian continent in the Mesozoic era is proposed. The Zagan MСС was formed in the Cretaceous period on the southern flank of a high mountain uplift of Western Transbaikalia, composed of late Paleozoic granitoids of the Angara–Vitim batholith. According to 40Ar/39Ar dating of amphiboles and micas from the mylonite zone, the active development time of the Zagan MCC corresponds to the early Cretaceous epoch (131, 114 Ma). The tectonic exposure of the core from about 15 km to the depths of about 10 km occurred at a rate of tectonic erosion of 0.4–0.3 mm/year as a result of post-collisional extension of the Mongol–Okhotsk orogen. Apatite fission-track dating shows that further exhumation and cooling of the rocks to about 3 km occurred in the lower-upper Cretaceous epoch (112, 87 Ma). The erosional denudation rate was about 0.3 mm/year.MCC- metamorphic core complexes, AFT- apatite fission-track

Based on geological and geophysical data, a lithological and stratigraphic section of the basement and sedimentary cover of the Alakol basin was compiled, detailing the lithological and paleogeographic settings. Oil source rocks, reservoirs and seals are identified. The tectonic zoning scheme is substantiated, the structural characteristics of the faults and the lithologic-facial features of the section are given. A complex multi-stage tectonic evolution has been identified. Potentially promising stratigraphic oil and gas complexes have been identified – Jurassic (Mesozoic) and Upper Devonian (Famennian) – Lower Carboniferous-Permian (Paleozoic). The deep structure of the region is illustrated by a geological and geophysical section. The correlation of the stratigraphic range of hydrocarbon potential of the Alakol basin was carried out. A probabilistic forecast for the search for crude hydrocarbons is substantiated. On this geological and geophysical basis, the design of the borehole was developed and its position for opening the cover and basement rocks was outlined.

Global fore- and sub-arc peridotites show paradoxically highly melt-depleted yet silica-enriched (as excess orthopyroxene) compositions, which have been attributed to either silica-enriched mantle sources or metasomatic overprints by silica-rich fluids/melts. Here, we present robust mineralogical evidence from an ophiolitic peridotite suite and thermodynamic modeling suggesting that boninitic melt percolation is a viable manner to induce silica enrichment and keep the ultra-depleted signature in a nascent lithospheric mantle wedge. The co-occurrence of resorbed olivines and euhedral high-Cr# spinels with a boninitic origin enclosed by porphyroblastic orthopyroxenes in these peridotites documents that the primary olivines were partially melted or dissolved along with precipitation of the euhedral spinels and growth of the orthopyroxene through reactions between the depleted peridotites and boninitic melts. Such metasomatism modulates the geochemistry of mantle wedges and can explain the compositional variations observed in the majority of global fore- and sub-arc peridotites and supra–subduction zone ophiolitic counterparts. Lateral assembly of these mantle domains by accretionary orogenesis may contribute to the growth of continental lithosphere and accounts for the existence of melt-depleted yet silica-enriched mantle domains beneath orogens.

Проведен анализ проявления магматизма в зоне перехода от континентальной окраины Камчатки к Курильской островной дуге и геофизических параметров погружающейся под них океанической плиты Северо-Западной Пацифики. Наличие прибрежного вулканического комплекса миоценового возраста в основании вулканического пояса Южной Камчатки способствует интенсивным коровым процессам, которые, вероятно, привели к формированию кальдерообразующих извержений в голоцене. Для Северных Курил характерно формирование ареального вулканизма, приуроченного к разрывным нарушениям земной коры. Аномальным является отсутствие вулканизма на о. Шумшу, расположенном непосредственно вблизи Камчатки. Отсутствие вулканизма на этом острове связывается с высокоскоростной аномалией, фиксируемой по данным сейсмотомографии. На основе представленных данных выдвигается предположение о наличии океанического поднятия на слэбе, погружение которого привело к дезинтеграции зон плавления, отвечающих за формирование вулканизма. Magmatism manifestations in the transition zone from the continental margin of Kamchatka to the Kurile island arc and some geophysical parameters of the subducted oceanic plate of the Northwestern Pacific are considered. The presence of the Miocene coastal volcanic (Pribrezhny) complex at the base of the South Kamchatka volcanic belt contributes to intense crustal processes causing caldera-forming eruptions in the Holocene. The Northern Kuriles are characterized by initiation of areal volcanism associated with crustal fault zones. Anomalous is the absence of volcanism on Shumshu island proximal to Kamchatka. Seismic tomography data reveal a high seismic velocity anomaly below it, which can explain this phenomenon. Based on the presented data an assumption is made about existence of a seafloor elevation on the slab, whose submergence led to disintegration of the melting regions responsible for generation of volcanism.

Thermochronological reconstructions of the Zagan metamorphic core complex were carried out using samples from the central part of the core, mylonite zone detachment and lower nappe with U/Pb zircon dating, 40 Ar/ 39 Ar amphibole and mica dating, and apatite fission-track dating. In the tectonothermal evolution of the metamorphic core, there was distinguished an active phase (tectonic denudation) of the dome structure formation during the Early Cretaceous (131–114 Ma), which continued in the Late Cretaceous – Paleocene (111–54 Ma) in passive phase (erosive denudation). During an active phase, there was initiated a large-amplitude gently dipping normal fault (detachment), which was accompanied by tilting (sliding of rocks along subparallel listric faults). As a result, about 7 km thick rock strata underwent denudation over 17 Ma at a rate of about 0.4 mm/year. In passive phase, about 6 km thick rock strata were eroded over 57 Ma, with a denudation rate of about 0.1 mm/year. Thus, the Zagan metamorphic core complex was tectonically exposed from the mid-crust to depths of about 9 km in the Early Cretaceous as a result of post-collisional collapse of the Mongol-Okhotsk orogen. Further cooling of the rocks in the metamorphic core to depths of about 3 km occurred in the Late Cretaceous – Pliocene as a result of destruction of more than 6 km high mountains.

The thermal history of the Late Paleozoic granitoids of the Angara–Vitim batholith (AVB) was reconstructed using a comprehensive approach including U/Pb, 40Ar/39Ar, and fission track dating methods. The rocks of the Barguzin and Chivyrkui complexes were studied at sites in the southwestern and northeastern parts of the batholith, as well as on the Svyatoi Nos Peninsula and the eastern shore of Lake Baikal. A generally similar thermal history is reconstructed for the rocks of all sites. The steep slope of the thermal history curve immediately after the formation of the AVB rocks indicates an epoch of intensive denudation which removed about a 5- to 7-km-thick stratum and was related to the Late Paleozoic orogeny. After the epoch of tectonic stabilization, characterized by the gradual closure of the biotite isotope system in the time period of 170–295 Ma, the closure of the feldspar/plagioclase isotope system occurs in the time period of 140–167 Ma. This interval coincides with the closure of the Mongol–Okhotsk Ocean and the onset of the formation of the Mongol–Okhotsk orogen and is characterized by denudation of an about 3-km-thick rock sequence. Then, in the period of 60–3 Ma ago, a slow denudation took place in the territory of the Transbaikalian region, which ended with a relatively abrupt cooling of rocks during the last 3 Ma and denudation of about 2- to 3‑km-thick stratum. This might be due to the remote tectonic impact of the Indo-Eurasian collision. The obtained data on the tectonic-thermal evolution of the AVB rocks can serve as a basis for correlating the formation of the Mongol–Okhotsk orogen and sedimentation in the Jurassic–Early Cretaceous Irkutsk, Kansk–Achinsk, Tuva, Kuznetsk, and West Siberian basins.

The tectonothermal evolution of Transbaikalia is reconstructed using U/Pb, Ar-40/Ar-39, and apatite fission track thermo-chronology of samples from the Late Paleozoic Angara-Vitim granitoid batholith (AVB). Successive closure of the zircon and amphibole isotope systems provides evidence that the AVB rocks cooled down rapidly soon after crystallization and 7-4 km of rocks were denuded subsequently during an extensive late Paleozoic orogeny in southern Siberia. The isotopic system of feldspar closed in the Middle Jurassic-Early Cretaceous (170-140 Ma) after a period of tectonic stability and slow closure of the biotite isotopic system in the early Permian-Middle Jurassic (295-170 Ma). The 170-140 Ma span was the time when the Mongol-Okhotsk orogen began its evolution, and the orogeny caused denudation of similar to 3 km of rocks. Denudation was slow in the Paleogene-Miocene (60-5 Ma) but accelerated over the past 5 million years (a similar to 3-2 km thick layer) during rapid cooling of rocks and activity under a far-field effect of the India-Eurasia collision.

In the Bouvet Island region (South Atlantic), a hotspot operates in the region of the triple junction of midocean ridges. On the basis of laboratory modeling data, the structure of the conduit of a thermochemical plume melting out in the mantle from the core-mantle boundary is presented. The thermal power of the Bouvet thermochemical plume is determined from the volume of uplifted and erupted rocks above the lower topographic level. To determine the mass flow rate of the melt for the plume, a topographic profile is used in a section perpendicular to the Bouvet hotspot trajectory and passing through the Bouvet plume. The thermal power of the Bouvet plume is 1.7 10(10) W. Based on the obtained power, the plume diameter is d = 10-13 km. The Bouvet plume belongs to intermediate-power plumes. Such plumes are diamondiferous, because their eruption on the surface transports the melt from a depth of >150 km, at which diamond is stable. The Bouvet plume trajectory originates in South Africa. Initially, the melt erupted on the cratonic surface through a diatreme. Next, the plume was preserved in the region of the drifting oceanic lithosphere and became no longer diamondiferous. The following morphostructures of the triple junction region with contrasting types of magmatic systems are distinguished according to petrological and geochemical data: MOR and the Bouvet volcanic island, which results from the plume activity. For the Bouvet region, K-2 (0.5%) and (2) (up to 0.9%) are identified in the composition of the deep magmatic melt. There is enrichment in H2 up to 100 ppm (up to 50 ppm in the Mid-Atlantic Ridge (MAR)) and in CH4 up to 12 ppm (up to 1 ppm in the MAR). Thus, it is suggested by the specific features of the melt composition that the Bouvet Island plume is thermochemical. This paper also presents a diagram showing free-convective flows in the asthenosphere in the Bouvet Triple Junction region. Sections are constructed on which the association between the convective structure and bottom morphostructures in the Bouvet region is identified. Large-scale asthenospheric flows are responsible for the formation of MOR. Convective rolls at the top of the asthenosphere account for the formation of the Bouvet and Moshesh transform faults. The Bouvet plume is under the influence of the ascending upper-mantle flow confined to the MOR axis and locally intensifies the ascending flows of the asthenospheric rolls.

Magmatism manifestations in the transition zone from the continental margin of Kamchatka to the Kurile island arc and some geophysical parameters of the subducted oceanic plate of the Northwestern Pacific are considered. The presence of the Miocene coastal volcanic (Pribrezhny) complex at the base of the South Kamchatka volcanic belt contributes to intense crustal processes causing caldera-forming eruptions in the Holocene. The Northern Kuriles are characterized by initiation of areal volcanism associated with crustal fault zones. Anomalous is the absence of volcanism on Shumshu Island proximal to Kamchatka. Seismic tomography data reveal a high seismic velocity anomaly below it, which can explain this phenomenon. Based on the presented data an assumption is made about existence of a seafloor elevation on the slab, whose submergence led to disintegration of the melting regions responsible for generation of volcanism.

We present seismic tomography models of the Baikal Rift Zone (BRZ), obtained from regional seismological data recorded in the period 1994-2016. 3D models of P- and S-wave velocity distributions under the BRZ were built down to a depth of 60 km with the LOTOS local seismic tomography algorithm. An overall picture of the heterogeneities coincides with the already existing ideas on the seismic structure of the region: a high-velocity anomaly in the north corresponds to the Siberian Craton; low-velocity anomalies in the western part of the study area are apparently due to the presence of the Cenozoic plume; the Baikal Rift Zone is characterized by a low-velocity anomaly down to a depth of 35-50 km, which accords with the present-day concepts of the Moho discontinuity depth. Moreover, below the BRZ there is a jump in the lower boundary of the low-velocity anomaly, which is in line with the Moho jump recognized in the existing investigations. In addition, based on the results obtained, we identified a number of heterogeneities not revealed earlier. For example, high-velocity near-surface anomalies in the Middle Baikal block, which were interpreted as heavy gabbro-metagabbro bodies, displaced as a result of the Cenozoic strike-slip. Based on the results obtained, as well as on the review of the existing geological and geophysical works, the authors argue in favor of a passive model during the formation of the Baikal Rift.

The new results have been represented of mineralogical–geochemical and geochronological studies of rocks of the Yehe-Shigna ophiolite massif located in the Tuva-Mongolian microcontinent in the northern part of the Central Asian orogenic belt (Eastern Sayan, Southern Siberia). The Yehe-Shigna ophiolite massif is part of the Belsk-Dugda ophiolite belt. The structural position, age, and geochemical characteristics of the belt indicate its formation in the setting of the back-arc basin of the Shishkhid intraoceanic island arc, developing in the period of 810–750 million years. It is assumed that together with the same-age formations of the Oka accretion wedge and the Sarkhoi active margin, it formed on the convergent margin of the Gondwana supercontinent. Its basement is represented by the Archean-Early Precambrian crystalline rocks and carbonate cover (“Gargan Glyba”). The gold-bearing Neoproterozoic deposits with dominant gold-telluride assemblages are localization in large ophiolites thrust zones along with the frame of the “Gargan Glyba”. They are allochthonous with respect to the Late Neoproterozoic-Cambrian Tuva-Mongolian island arc of the Siberian continent. A similar type of gold deposit is probably worth looking for ophiolites thrust zones in other Precambrian Gondwana-derived microcontinents.

During the Late Precambrian-Palaeozoic the southern Siberian continent bordered on the Palaeopacific and Palaeoasian Ocean tectonic plates. Their interactions led to the formation of the complex Central Asian folded (orogenic) belt containing the Silurian Tuvaella and Retziella brachiopod fauna. The subduction of the Palaeopacific plate under the Siberian continent led to the formation of the Late Precambrian-Palaeozoic accretionary orogen. The subduction of the Palaeoasian Ocean plate, including Gondwana-derived continental blocks, under the Siberian continent, created in the Late Precambrian-Ordovician a composite Kazakhstan-Baikal continent (collisional orogen). The Late Precambrian-Early Palaeozoic Ob'-Zaisan ocean basin was located between the Kazakhstan-Baikal and the Siberian continents. On site of the Ob'-Zaisan ocean basin the amalgamation and collision of these two continents resulted in the formation of the Early Palaeozoic Ol'khon suture-shear zone in the Baikal region, the Middle Palaeozoic Charysh-Terekta-Ulagan-Sayan suture-shear zones in the Altai-Sayan region, accretional and island arcs in Junggar and East Kazakhstan. The Silurian Tuvaella brachiopod fauna inhabited the Ob'-Zaysan ocean basin coastal outskirts, the epicontinental sea and active margins of the Kazakhstan-Baikal continent in subtropical-temperate latitudes. To this continent, the Gondwana-derived continental blocks with the Silurian Retziella brachiopods fauna have been accreting since the Late Palaeozoic. The Silurian Retziella brachiopod fauna inhabited shallow epicontinental marine areas of the continental blocks (Tarim, North China, South China, Australia and New Zealand) during the rifting of Gondwana separated from the Siberian continent by the Mongol-Okhotsk Ocean.

The formation of mountain system and neotectonic structure of the Altai-Sayan region is regarded to be a result of intercontinental deformations,related to a distant effects of tectonic stress from the Indo-Eurasian collision.Within this tectonic model we carried out the joint analysis of the geology,seismicity data and topographic materials enable to assume that the maximum changes in the relief and seismic activity in the northern part of Central Asia mountain belt are confined to the zones of intersections of the Late Paleozoic regional faults.The intersections and junctions of faults should be considered as one of the most important structural factors that increase the fragmentation of the substrate,affect changes in the local stress field and predetermine the localization of large earthquake foci with a magnitude M ≥ 5.Some regularities were revealed,based on the example of helium and travertine manifestations in the junction zone of the Charysh-Terekta and Kurai regional faults,which can be used as precursors of earthquakes.

The stages of the formation of mountain systems (orogens) and sedimentary basins of Asia are highlighted and an analogy is given. The stages are manifested in the Jurassic, Cretaceous, and Cenozoic as a result of collisions to the southern active margin of the Asian continent, respectively, of the Quingtang, North China, and Indian continental blocks, which led to the formation of large intracontinental orogenic belts that are the source of sedimentary basin demolition.

The use of satellite-geological information permits generalization of studies of various active geologic processes in a new way. As reference examples, we consider geologic regions extensively covered by research with our contribution. The joint use of satellite images, maps of gravity anomalies, and seismic-tomography data for Kamchatka made it possible to construct 3D models of surficial and deep-seated (depths from 10-50 to 650 km) volcanic structures. For young volcanosedimentary structures of Kamchatka, it is possible to trace the interaction of various processes, from crystallization of magmas in magma chambers to ore and oil formation in calderas. Ancient tectonic structures and superposed Cenozoic deformations in the Tien Shan, Altai, and Baikal regions are clearly displayed in satellite images and on maps of gravity anomalies. The long-range impact of the Indo-Eurasian collision on the Tien Shan, Altai, and Baikal regions was expressed as shearing, which resulted in the most contrasting structures in the zones of junction of regional faults and along the framing of cratonal structures. The active structures of Gomy Altai contain numerous travertines, whose abundance is correlated with seismic activity. The mass formation of methane and gas hydrates in Lake Baikal might be related to mantle plume fluids.

The causes of delamination of the mantle lithosphere in collision zones is actively debated in the scientific community. The main discussions are focused on the initiation of sinking of the continental lithosphere into the asthenosphere to a depth. Most scientists believe that such kind of immersion is impossible. However, there are several articles showing that this process is nonetheless taking place. For example Kay and Kay, (1993), Faccenda, Minelli, Gerya, (2009), Ueda et. al., (2012) and others propose various mechanisms of delamination, for example: eclogitization of the mafic layer of the lower crust, the effect of convection in the upper mantle, or gradual transition of the oceanic subduction into continental collision. Does the mantle part of the lithosphere sink into the mantle or spread laterally, as described in [for example, Deep Geodynamics, 2001; Bird, 1991; Schmeling and Marquart, 1991]?To answer these questions, we study deep structures beneath the Caucasus and Kyrgyz Tien Shan collision zones. The studies were carried out on the basis of multiscale seismic tomography methods: regional and global. This approach made it possible to study heterogeneities both in the crust and in the upper mantle. The obtained 3D models of seismic heteroheneities reveal similar features for the both collision regions. Beneath the mountain areas, in the uppermost mantle and lower crust, we observe prominent low-velocity anomalies that possibly indicate thickening of the crust and missing (or strongly thinned) mantle part of the lithosphere. At the edges of the collision zones, we reveal inclined high-velocity anomalies appearing as continuations of the continental plates sinking underneath the collision zones, which can be interpreted as delaminating mantle parts of the continental lithosphere. Based on joint consideration of the tomography models with the existing models of tectonic evolution, we conclude that the mechanisms of delamination in the considered two regions are different. In Caucasus, the delamination could be gradually transformed from oceanic subduction that ended here approximately ~10-15 Ma. In the case of Tien Shan, the detachment of the mantle lithosphere could be triggered by the plume that existed beneath Central Tien Shan or by the eclogitization of the mafic layer of the lower crust.

In the Kurai ridge located in the southeastern Gorny Altai (Altai Mountains, Russia) metamorphic rocks of the Kurai complex are widely developed: granite‐gneisses, crystalline schists and amphibolites, including widespread Early Carboniferous mylonites and blastomylonites. Oriented samples of blastomylonites were taken from the upper reaches of the Kuraika river for the microstructural study aimed to determine the kinematics of movements. The analyses of thin cut samples show structural‐kinematic indicators that suggest two deformation events (left‐lateral shearing, then right‐lateral shearing).

—The Transbaikalian region comprises several known geologic structures: the Mesozoic Mongolia-Okhotsk orogen, the Cenozoic Baikal rift system, and the world largest Angara–Vitim granitic batholith. They all formed upon heterogeneous Neoproterozoic– Early Paleozoic continental-margin complexes of the Siberian craton. The region is subject to the influence of mantle plumes, which induced Mesozoic–Cenozoic volcanism and controlled structural and lithological changes in the crust in the early history. Transbaikalia, which has been a scene of multiple tectonic events, is a model area for geophysical (in particular, gravity) surveys for various geological and geodynamic applications. As a novel approach, we interpret geological and geodynamic data from the region with reference to the pattern of free-air and Bouguer gravity anomalies revealed by satellite altimetry. Bouguer anomalies highlight large structures in the lithospheric mantle which were produced in the Cenozoic mainly by the activity of mantle plumes. Basaltic lava fields were confirmed to be almost coeval with mantle anomalies and to record the presence of the plume head at the crustal base. However, the origin of the Late Paleozoic Angara–Vitim granitic batholith was only tentatively attributed to the plume activity, based on gravity data. Mesozoic metamorphic core complexes (MCC) and basins that formed during the evolution of the Mongolia–Okhotsk orogen show up clearly on the map of free-air anomalies. Most of the MCC revealed in Transbaikalia coincide with oval gravity highs and border negative elongate features corresponding to Mesozoic basins. The zone of Cenozoic tectonism stands out in the pattern of free-air anomalies as maximum gravity contrasts, with the values changing from –110 to –120 mGal in basins to + 90 or +100 mGal in ranges. This zone encompasses rift basins filled with Cenozoic or, locally, Mesozoic sediments, which jointly form a domino-like system of rhomb-shaped structures typical of the Baikal rift system and, in general, of Cenozoic Central Asia resulted from the far-field effect of the India–Eurasia collision.