Pleistocene-Holocene Monogenetic Volcanism at Malko-Petropavlovsk Zone of Transverse Dislocations on Kamchatka: Geological Setting, Spatial, Geochemical Paticular Features and Potential Volcanic Hazards

Based on government statistical data ~80% of the local Kamchatkan population (~250 ka people) live in the major cities on the coastal line of Avacha Gulf . It is the main transport seaway to Kamchatka , and and important Asia - North America air transport corridor. The Avacha Gulf is located in the Malko-Petropavlovsk zone of transverse dislocations (MPZ) on the extension of deep transform fault on the boundary between various ly aged slabs. Most of monogenetic cinder cones chaotic distributed in relation to the trench and belong to the long-living rupture zones of MPZ. Some of the monogenetic volcanoes are parasitic cones on the slopes of Koryaksky and Avachinsky stratovolcanoes and related with their magma plumbing systems. We here present new results of the geochemical and isotopic stud ies of monogenetic volcanism in MPZ. Based on whole rock and trace element geochemistry, Sr-Nd-Pb isotopic ratios of monogenetic volcanism, ­­ magmas were shown to sample the enriched mantle source with dominance decompression melting without significant inputs of the slab`s components. Calculations of the P, T conditions suggest magma residence of monogenetic cinder cones on the Moho boundary. That correlates with the geophysical observation of crustal discontinuity under the MPZ. Monogenetic cinder cones have an active magma plumbing system because during the Holocene time were several periods of activations. Presented results show necessary install continuous monitoring of environment changing around the Avacha Gulf and more serious attention from government and science. A more detailed investigation of MPZ will help degrease potential risks of eruptions from monogenetic volcanoes for human and infrastructures.

Most important results of the scientific activity of the Seismological Division GS RAS in 2016-2020 (seismic research)

The article presents the most important results of seismic studies carried out in 2016-2020 at the Seismological Division GS RAS. Work at the Chirkey’s HPP, where natural oscillations of the dam and their seasonal changes were studied in detail and a method for monitoring the natural frequencies of the structure was developed. Research at the Sayano-Shushenskaya HPP, where the processes of interaction of operating hydroelectric units with surrounding structures were studied and it was found that under certain operating conditions of the equipment, there is a 10-20-fold increase in the natural oscillations of the dam, the source of which is natural oscillations (organ vibrations) in the penstocks. A method has been developed for assessing the response of structures to seismic impacts, based on the method of coherent reconstruction of standing wave fields and allowing to calculate the vibrations of an object arising from seismic impacts at its base. The possibilities of determining the natural vibrations of large objects based on low-frequency seismological records and their monitoring are demonstrated on the example of the results of the analysis of satellite images and seismological materials when determining the causes of the landslide on the Elbashinsky dump of the Kolyvan anthracite deposit in the Novosibirsk region. The possibility of using river seismic data to study the structure of the earth’s crust at all depth, including the Moho boundary, has been substantiated using the example of data obtained during the development of the CDP-2D profile in the lower reaches of the river Lena.

The latest 3D density model of the Barents Sea crust

<p>The 3D gravity inversion was realized in order to reveal the density features of the Earth's crust the Barents Sea. The original 3D density model of the region includes both lateral and depth density`s changes.<br>The main steps of the modelling are:</p><p>- The calculation of the anomalies of the gravity field in Bouguer reduction with the three-dimensional gravitational effect correction of the seabed.</p><p>- Gravity field correction for the three-dimensional influence of the Moho boundary (according to the GEMMA model). The excess density at the Moho picked by minimizing the standard (root-mean-square) deviation of the gravity effect from GEMMA Moho boundary and Bouguer anomalies. So, the regional density jump at the Moho border is 0.4 g / cm<sup>3</sup>.</p><p>- Based on regional geological and geophysical data about the deep structure of the Barents Sea, it was developed generalized dependence of density changes by depth in the sedimentary cover and the consolidated part of the earth's crust.</p><p>- Compilation of 3D original model of the base of the sedimentary cover on predictive algorithms of neural networks. The neural network was trained on several reference areas located in different parts Barents area using a number of potential fields transformations and the bottom of the sedimentary cover from model SedThick 2.0.</p><p>- Using the resulted dependence of the crust density change by depth and a new model of the sedimentary cover bottom, the gravitational field corrected for the impact of the sedimentary cover with variable density.</p><p>- The finally stripped gravity field is used to create density model above and below the base of the sedimentary cover. Frequency filtering on Poisson wavelets [Kuznetsov et al., 2020] had been used for the final separation of the gravitational field into its components.</p><p>- The inverse task was solved using specialized volumetric regularization [Chepigo, 2020].</p><p>As a result, the crust of the Barents Sea density inhomogeneities were localized by depth and laterally in 3D model, which became the basis for further structural-tectonic mapping.</p><p>References</p><p>Chepigo L.S. GravInv3D [3D density modeling software]. Patent RF, no. 2020615095, 2020. https://en.gravinv.ru/</p><p>Kuznetsov K.M. and Bulychev A.A. GravMagSpectrum3D [Program for spectral analysis of potential fields]. Patent RF, no. 2020619135, 2020.</p>

Seismic Density Model of the White Sea’s Crust

Study of the deep structure of the White Sea region is relevant to active geodynamics, manifestations of kimberlite magmatism, and the prospects of oil and gas searches. The aim of this work was to model the velocity and density structure of the earth’s crust in the White Sea region. Modelling was carried out using the known data of instrumental observations and the software complex “Integro”. With the help of 2D models based on deep seismic sounding (DSS) profiles and a digital map of the anomalous gravity field, the density structures of local areas of the region’s crust were refined. A 3D density model was built. Within the framework of this model, the positions of the density layers were determined. The relief of the Mohorovichich (Moho or M) discontinuity reflects the anomalies of the gravity field. Depression of the Moho boundary in the bottleneck of the White Sea indicates the vertical structure of the earth’s crust associated with manifestations of kimberlite magmatism.

3-D thermochemical structure of lithospheric mantle beneath the Iranian plateau and surrounding areas from geophysical–petrological modelling

SUMMARY While the crustal structure across the Iranian plateau is fairly well constrained from controlled source and passive seismic data, the lithospheric mantle structure remains relatively poorly known, in particular in terms of lithology. Geodynamics rely on a robust image of the present-day thermochemical structure interpretations of the area. In this study, the 3-D crustal and upper mantle structure of the Iranian plateau is investigated, for the first time, through integrated geophysical–petrological modelling combining elevation, gravity and gravity gradient fields, seismic and petrological data. Our modelling approach allows us to simultaneously match complementary data sets with key mantle physical parameters (density and seismic velocities) being determined within a self-consistent thermodynamic framework. We first elaborate a new 3-D isostatically balanced crustal model constrained by available controlled source and passive seismic data, as well as complementary by gravity data. Next, we follow a progressively complex modelling strategy, starting from a laterally quasi chemically homogeneous model and then including structural, petrological and seismic tomography constraints. Distinct mantle compositions are tested in each of the tectonothermal terranes in our study region based on available local xenolith suites and global petrological data sets. Our preferred model matches the input geophysical observables (gravity field and elevation), includes local xenolith data, and qualitatively matches velocity anomalies from state of the art seismic tomography models. Beneath the Caspian and Oman seas (offshore areas) our model is defined by an average Phanerozoic fertile composition. The Arabian Plate and the Turan platform are characterized by a Proterozoic composition based on xenolith samples from eastern Arabia. In agreement with previous studies, our results also suggest a moderately refractory Proterozoic type composition in Zagros-Makran belt, extending to Alborz, Turan and Kopeh-Dagh terranes. In contrast, the mantle in our preferred model in Central Iran is defined by a fertile composition derived from a xenolith suite in northeast Iran. Our results indicate that the deepest Moho boundary is located beneath the high Zagros Mountains (∼65 km). The thinnest crust is found in the Oman Sea, Central Iran (Lut Block) and Talesh Mountains. A relatively deep Moho boundary is modelled in the Kopeh-Dagh Mountains, where Moho depth reaches to ∼55 km. The lithosphere is ∼280 km thick beneath the Persian Gulf (Arabian–Eurasian Plate boundary) and the Caspian Sea, thinning towards the Turan platform and the high Zagros. Beneath the Oman Sea, the base of the lithosphere is at ∼150 km depth, rising to ∼120 km beneath Central Iran, with the thinnest lithosphere (<100 km) being located beneath the northwest part of the Iranian plateau. We propose that the present-day lithosphere–asthenosphere topography is the result of the superposition of different geodynamic processes: (i) Arabia–Eurasia convergence lasting from mid Jurassic to recent and closure of Neo-Tethys ocean, (ii) reunification of Gondwanian fragments to form the Central Iran block and Iranian microcontinent, (iii) impingement of a small-scale convection and slab break-off beneath Central Iran commencing in the mid Eocene and (iv) refertilization of the lithospheric mantle beneath the Iranian microcontinent.

THE MODERN GEODYNAMICS OF THE MIDDLE AND SOUTHERN PART OF CASPIAN SEA

Статья посвящена изучению геодинамики Азербайджанской части Среднего и Южного Каспия на базе современной изученности о геоструктуре исследуемого региона с обоснованными результатами анализа ее геологического строения, GPS данных, сейсмической активности и механизмов очагов землетрясений. Установлено, что основная масса скопления землетрясений сосредоточена в зоне псевдо-субдукции. Очаги погружаются до глубины 70 км. Большая часть землетрясений располагается ниже границы Мохо, что говорит о глубоких корнях Апшероно-Прибалханской подвижной системы. Результаты определения механизма очагов землетрясений показали, что для территории Центрально-Каспийской впадины для малых значений углов осей растяжения характерны большие углы осей сжатия, что свидетельствует о преобладании там сбросо-сдвиговых подвижек. Таким образом, можно сказать, что сейсмические процессы в зоне Апшероно-Челекенского глубинного разлома вызваны одними и теми же причинами – активными тектоническими движениями на границе двух крупнейших структур земной коры региона – Скифско-Туранской плиты и Копетдагско-Кавказской складчатой подвижной области. The article dedicated to the study of geodynamics of the Azerbaijan part of the Middle and Southern Caspian Sea on the basis of the modern study of the geological structures of the region studied with reasonable results of the analysis of its geological structure, GPS data, seismic activity and earthquake focal mechanisms. It was found that the majority of the cluster of earthquakes concentrated in the pseudo-subduction zone. The foci of earthquakes are immersed to the depth of 70 km. Most of the earthquakes is below the Moho boundary, which indicates the deep roots of Apsheron-Balkhan moving system. The results of the mechanism of the earthquakes have shown that for the territory of Central Caspian depression for small angles of the axes of stretching values are typical large-angle compression axis, indicating that the prevalence there is strike-slip shifts. Thus, we can say that the seismic processes in the Absheron-Cheleken deep fault zone caused by the same reasons – with active tectonic movements on the border of two of the largest structures of the Earth’s crust in the region – Scyphian-Turan plate and Kopetdag-Caucasian folded movable area.