Vol 509, No 1 (2023)

Geochemical, geochronological (U-Pb on ID TIMS zircons), and isotope-geochemical (Sm-Nd) studies of the Kopri-type granitoids of the Tukuringra Complex have been done. The granitoids localized exclusively in the zone of the Dzheltulak suture, which separates the Dzhugdzhur-Stanovoy and West Stanovoy superterranes of the Central Asian fold belt. It has been established that they can be classified as postcollision granitoids of elevated alkalinity and basicity of the adakite type, formed in the age range of 127 ± 1–126 ± 1 Ma, which are part of the Late Mesozoic postcollision Stanovoy volcano-plutonic belt extending in the sublatitudinal direction from the Sea of Okhotsk inland continent subparallel to the Mongolo-Okhotsk suture zone for more than 1000 km and stitching the Dzhugdzhur-Stanovoy and West- Stanovoy superterranes. The structural position of massifs of the Kopri-type granitoids fixes the upper age boundary of the formation of the Dzheltulak suture. The formation of the initial magmas of these granitoids is connected with an essentially lithospheric source formed as a result of mixing of the Early Precambrian and younger, apparently, Phanerozoic component. The similarity in the Nd isotopic composition of the granitoids of the Kopri-type with similar in composition and age granitoids of the West Stanovoy superterrane most likely indicates the similarity of their sources, as well as the fact that the Dzheltulak suture zone “plunges” in the northeast direction under the structures of the Dzhugdzhur–Stanovoy superterrane. This is in full accordance with modern ideas about the features of the deep structure of the junction of the Eurasian and Amur lithospheric plates.

Based on geochemical analyses of tectonic pseudotachylytes and their host rocks the features of redistribution of major, rare and rare-earth elements during seismogenic frictional melting of arkose-type metaterrigenous rocks from different-temperature zones of regional metamorphism) of Northern Ladoga region are considered. Multidirectional trends in variations of the major elements oxides contents in the triad protolith-blastocataclasite-pseudotachylyte were revealed, but a unidirectional increase of the frictional melt basicity in comparison with the protolith was established. Geochemical evidence of partial selective melting of source rocks is considered. Peculiarities of rare and rare-earth elements fractionation during transition to the melt of protolithic material, as well as during its subsequent partial crystallization are shown. The appearance of positive europium anomaly in the melt matrix of all three sampling points is noted. By changes of these elements’ concentrations in zones of pseudotachylyte substrate generation and in areas of its injection their differential mobility during frictional melting in a zone of dynamic movement is estimated.

Secondary inclusions of carbonate melt were studied in garnets and clinopyroxenes from ultrahigh pressure calc-silicate rocks. Secondary inclusions are located in healed cracks associated with large (100 µm – 3 mm) carbonate inclusions in garnet. In some cases, healed cracks intersect inclusions of potassium-bearing clinopyroxene in garnet. Since the amount of K₂O in healed cracks in clinopyroxene-inclusions reaches 0.64 wt. %, it was concluded that their formation and healing occurred at the ultrahigh pressure metamorphic stage. Raman spectra interpretation of secondary carbonate melt inclusions in garnet and clinopyroxene confirmed the presence of the following phases: methane, graphite, calcite, dolomite, muscovite, and phlogopite. The obtained results imply for the ultrahigh-pressure metamorphic stage in the evolution of calc-silicate rocks from the Kokchetav massif, corresponding to the methane accumulation in the carbonate melt.

It was shown that at a pressure of 3.0–7.8 GPa and a temperature of 750–1030°C, a set of reactions occurred in carbonate-bearing and Cl-enriched pelite that is finally converted into eclogite-like assemblage and formed H₂O–CO₂ Cl-enriched fluid. The eclogite-like assemblage remains stable when P-T conditions change concordantly with hot subduction geotherms, whereas carbonate is completely dissolved in the fluid already at ≥5.5 GPa. In quenched fluid the content of CO₂ reaches 30 wt. %. However, preliminary defluidization of pelite at 3.0 GPa and 750°С leads to chlorine removal and carbonate stabilization at 5.5 GPa and at 7.8 GPa in equilibrium with the next chlorine-free portions of fluid. Thus, the stability of carbonates under P-T conditions typical of subduction zones is dependent on the behavior of chlorine during defluidization of marine sediments.

The paper provides a comprehensive analysis of the morphometric attribute “general curvature” for the bathymetry of the Barents Sea, seismic and seismoacoustic data containing in the wave field patterns tectonic faults emerging to the surface, a fault network of the sedimentary cover confirmed by seismic surveys, and seismotomographic data showing the heterogeneous deep structure by the distribution of seismic wave velocities in the upper mantle. The analysis of these data showed the presence of a causal relation between rheologically heterogeneous and mobile blocks of the upper mantle and the crystalline part of the Earth’s crust with the deep fault network, emerging on the bottom surface and being a relief-forming factor that forms characteristic domains with different textures performed by the morphometric attribute “general curvature”.

Ammonoids Paramexicoceras aldanense Popow were found at the base of the Nekuchan Formation (upper part of the Changhsingian Stage) in the Dyba River basin, South Verkhoyanie. The first discovery of goniatites in the Upper Permian of Northeast Asia made it possible to clarify the biostratigraphic subdivision of the boundary Permian-Triassic deposits. The Otoceras concavum Zone in its lower part is reduced due to the establishment of the Paramexicoceras aldanense Beds at the base of the Nekuchanian Regional Stage. The data obtained indicate that the genus Paramexicoceras, previously considered long-lived, belongs to the youngest and short-lived taxa of the Cyclolobidae, representing the terminal phase of the goniatite development. This record made it possible to compare the base of the Nekuchanian Regional Stage in South Verkhoyanie with the upper part of the Foldvik Creek Group in East Greenland.

Studies have been conducted on the variations of ambient noise recorded by broadband and short-period seismic stations in the area of South Baikal before and after the large December 9, 2020 Kudara earthquake with M_w = 5.6. 10 days before the earthquake, there was a gradual increase of oscillation amplitudes in the frequency range from 0.01 to 0.1 Hz, with an increasing background observed also during 4 days after the main shock (period from 01.12.2020 to 13.01.2021). The maximum amplitude increase is 19.5 against the background. During this time, there were recorded 48 aftershocks. The analysis of direction of particle motion in seismic waves over the reporting period showed an abrupt change in the orientation of oscillations, which is fully consistent with the azimuth for the main shock epicenter. The analysis of seismograms over the next period (from December 13) did not show similar effects in the ambient noise field. Apparently, the ambient noise field reflected the process of slow faulting before the earthquake and after the main shock with subsequent attenuation.

The transformation of a multicomponent barotropic tide in the Sea of Okhotsk is considered in the framework of fully nonlinear non-hydrostatic calculations. The data of the tidal model and parameterized bottom topography and vertical profiles of sea water density based on data from open international atlases are used to initialize the model. Estimates of the wave amplitudes of the diurnal and semidiurnal baroclinic tides in terms of the displacement of isopycnal surfaces at different horizons are obtained and presented in the form of geographical maps. It is shown that the distribution of amplitudes significantly depends on depth, has a complex spatial structure with a noticeable predominance of the amplitudes of baroclinic waves of the diurnal period and the main extrema located on the shelf opposite Cape Elizabeth, Okhinsky Isthmus and Cape Patience. The implemented approach to mapping the amplitudes of internal tides can be applied to other shelf areas of the seas of the Russian Federation and used for predictions of these phenomena, including engineering assessments for the design and operation of marine infrastructure.

The methodological and technical possibilities of monitoring temperature fields on a thousand-kilometer track in the Sea of Japan using acoustic thermometry methods are presented. The proposed tomographic method for monitoring the dynamics and structure of water is based on the emission and reception of complex phase-shift keyed signals on a diagnosed path with the determination of the propagation time along various ray trajectories, followed by the calculation of the speed of sound and temperature. The physical prerequisites for the practical implementation of thermometric studies at large distances are based on the effect of an acoustic “mudslide” – the phenomenon of the transition of acoustic energy from the near-bottom shelf area to the underwater sound channel of the deep ocean. In the example of the Sea of Japan, a high-precision acoustic thermometry system based on tomographic schemes with mobile and stationary hydroacoustic emitters and receiving systems was proposed and experimentally tested.

The study and analysis of malacofauna from cores of bottom sediments and cores from the Azov spits showed the nature of the change during the transition from the Ancient Azovian to the New Azovian layers, the uneven distribution of communities in time and space. The shell material from littoral malacocenosis and shallow-water banks is the main component for the formation of spits. Based on a series of cores up to 25 m thick from the Dolgaya Spit, it is shown that its formation began about 2500 years ago, and carbonate material reflects the history of the development of the benthic fauna of the sea.

A hypothesis has been put forward about the formation of an increased dispersion of the concentration of substances polluting the water of the river flow under the influence of internal synergistic factors. The effect is manifested in the dispersion of controlled quality indicators, exceeding their average value, which in practice makes it difficult to manage water use. An assumption is made that such a dispersion is a consequence of the nonlinearity of systems that are far from thermodynamic equilibrium. It is possible that the driving force in this case is the turbophoresis of impurity particles in a turbulent, as a rule, water flow.

In this work, we show a trend of lengthening the period of high intensity of the Antarctic polar vortex in late spring and early summer (November–December), which has been traced over the past 30 years. This trend is observed both in the dynamics of the main characteristics of the polar vortex (vortex area and wind speed along the vortex edge) and in the Antarctic ozone hole area. A clear manifestation of this is the polar vortex dynamics in 2020, when there were unusually high wind speeds along the vortex edge throughout the entire period of its existence and record values of vortex area and ozone hole area from mid-November to December. In addition, the polar vortex existed until the last week of December, which is an unprecedented case. To analyze the Antarctic polar vortex dynamics, we used the vortex delineation method by geopotential values determined from the maximum temperature gradient and maximum wind speed characterizing the vortex edge.

Here we elaborate the method for retrieval of 2D spatial spectra of sea wave elevations using high-resolution satellite imagery. Such an elaboration allows us to assess angular distributions of wind wave energy. The method was validated based on the results of a comprehensive experiment that involved optical satellite imaging of the Black Sea water area and sea truth measurements under controlled conditions using a stationary oceanographic platform. Angular distribution of sea wave energy, retrieved by spatial spectra of satellite image fragments, were compared with the results of measurements of frequency-angular spectra using data from an array of string wave recorders. It has been demonstrated that the results of measurements by remote and in-situ methods are consistent in the range of sea wavelengths from 2.8 to 30 m, and the mean absolute error is 0.3.