Deep Earth Research Articles

Epidote as a conveyor of water into the Earth’s deep mantle in subduction zones: Insights from coupled high-pressure and high-temperature experiments

Abstract Epidote is a major hydrous mineral in subducted mafic oceanic crust. Understanding its stability in the subduction zone environment is important for evaluating its role as a conveyor of water into the deep Earth. Here we report experimental results on epidote by simulating the high-pressure-temperature (P-T) conditions of the plate subduction environment. We used a diamond-anvil cell with an external resistance heating system, combined with in situ X-ray diffraction (XRD) and Raman spectroscopy techniques. Experiments at ambient pressure and high temperatures indicate that epidote starts to decompose at 1223 K and breaks down completely at 1373 K. In situ XRD analyses show no phase transition at temperatures up to 1272 K and pressures up to 14.0 GPa. Raman spectra indicate that epidote is stable at 1272 K and 14.0 GPa, but the energies of two Si-O bonds (ν2,ν5) and one M-O bond (ν3) increase with increasing temperature. The cation H+ moves for a distance when the P-T is increased to 13.0 GPa and 1123 K. Based on the thermal structure of subducted slabs in typical hot and cold subduction zones, we infer that epidote can convey water downward into the mantle transition zone through subducted mafic oceanic crust.

Fe3+ -hosting carbon phases in the deep Earth

Iron-bearing carbonates play an important role in Earth's carbon cycle. Owing to their stability at mantle conditions, recently discovered iron carbonates with tetrahedrally coordinated carbon atoms are candidates for carbon storage in the deep Earth. The carbonates' iron oxidation and spin state at extreme pressure and temperature conditions contribute to the redox conditions and element partitioning in the deep mantle. By laser heating ${\mathrm{FeCO}}_{3}$ at pressures of about 83 GPa, ${\mathrm{Fe}}_{4}^{3+}{\mathrm{C}}_{3}{\mathrm{O}}_{12}$ and ${\mathrm{Fe}}_{2}^{2+}{\mathrm{Fe}}_{2}^{3+}{\mathrm{C}}_{4}{\mathrm{O}}_{13}$ were synthesized and then investigated by x-ray emission spectroscopy to elucidate their spin state, both in situ and temperature quenched. Our experimental results show both phases in a high-spin state at all pressures and over the entire temperature range investigated, i.e., up to 3000 K. The spin state is conserved after temperature quenching. A formation path is favored where ${\mathrm{Fe}}_{4}^{3+}{\mathrm{C}}_{3}{\mathrm{O}}_{12}$ forms first and then reacts to ${\mathrm{Fe}}_{2}^{2+}{\mathrm{Fe}}_{2}^{3+}{\mathrm{C}}_{4}{\mathrm{O}}_{13}$, most likely accompanied by the formation of oxides. Density functional theory calculations of ${\mathrm{Fe}}_{2}^{2+}{\mathrm{Fe}}_{2}^{3+}{\mathrm{C}}_{4}{\mathrm{O}}_{13}$ at 80 GPa confirm the experimental findings with both ferric and ferrous iron in high-spin state with antiferromagnetic order at 80 GPa. As the intercrystalline cation partitioning between the Fe-bearing carbonates and the surrounding perovskite and ferropericlase depends on the spin state of the iron, an understanding of the redox conditions prevalent in subducted slab regions in the lower mantle has to take the latter into account. Especially, ${\mathrm{Fe}}_{2}^{2+}{\mathrm{Fe}}_{2}^{3+}{\mathrm{C}}_{4}{\mathrm{O}}_{13}$ may play a key role in subducted material in the lower mantle, potentially with a similar role as silicate perovskite.

Hydrogen-rich gas discovery in continental scientific drilling project of Songliao Basin, Northeast China: new insights into deep Earth exploration

Hydrogen-rich gas discovery in continental scientific drilling project of Songliao Basin, Northeast China: new insights into deep Earth exploration

Chain Actions Generated High-Elevation and High-Relief Topography of the Eastern Margin of the Tibetan Plateau: From Deep Earth Forces to Earthquake-Induced Dams

High-elevation and high-relief topography is the most prominent geomorphological features of the eastern margin of the Tibetan Plateau. This paper proposes that the interaction of the endogenic and exogenic forces jointly determines the formation of such high and steep landform. Eastward propagation of the Tibetan Plateau has been portioned by NW-striking, large-scaled sinistral strike-slip faults due to resistance of rigid Yangtze craton to the east of the eastern margin of the Tibetan Plateau. The transpressional stress has emerged in eastern margin of the Tibetan Plateau and has resulted in several large-scale active faults. The transpressional behavior has changed the flowing direction of the rivers from NW-SE to nearly N-S. The transport capacity of these southward-flowing rivers decreases correspondingly. Since the late Cenozoic, intensive seismic events have occurred on the active faults of the eastern Tibetan Plateau which resulted in geohazards such as slope failures, landslides along these southward-flowing rivers. This resulted in the formation of a large number of dammed lakes in the eastern margin of the Tibetan Plateau. To a certain degree, these dammed lakes play an important role in lowering the upstream erosion rate and in accelerating downstream river incision which yields gravity unloading and uplift of the bedrock. The frequently and widely distributed damming events, therefore, forms an important supplementary factor with respect to the formation of high and steep landforms.

Electrical Conductivities and Association Constants in Dilute Aqueous NdCl3Solutions from 298 to 523 K along an Isobar of 25 MPa

Electrical measurements were performed in dilute aqueous NdCl3 solutions from 298 to 523 K along the 25 MPa isobar to obtain limiting conductances and association constants. The specific conductance data were estimated using a continuous flow cell and a Markov Chain Monte Carlo (MCMC) correction algorithm. The limiting conductances for the salts in water were derived by regressing the mean spherical approximation (MSA) conductance model and speciation analyses based on the MCMC algorithm and the Deep Earth Water (DEW) model. The limiting conductances derived from the experimental data agree well with a predictive correlation proposed by Smolyakov, Anderko, and Lencka. Only the first association constant between neodymium and chloride could be derived at low temperatures (< 373 K) due to the apparent large statistical uncertainty of the second association constant. Above 373 K, both association constants could be derived and show a reasonable agreement with Migdisov and Williams-Jones and Gammons et al.

The relationship between volcanism and global climate changes in the Tropical Western Pacific over the mid-Pleistocene transition: Evidence from mercury concentration and isotopic composition

Volcanoes are a significant component of the Earth system, influencing the interaction between oceans and the atmosphere over large spatial and temporal scales. Being a volcanically dynamic region, the Tropical Western Pacific (TWP) can significantly impact variations in global climate. However, high-resolution continuous records of volcanic activity in this region are lacking, resulting in significant uncertainties regarding the coupling between the deep earth, climate changes, and atmospheric CO2 in the TWP. To address this issue, mercury (Hg) levels, isotopic compositions, and Hg/total organic carbon (Hg/TOC) ratios were determined at site U1486 to track volcanic activity throughout the mid-Pleistocene transition (MPT) from 1.3 Myr to 0.6 Myr. Our results of anomalously high Hg concentrations and Hg/TOC ratios provide evidence of time-varying volcanism throughout the MPT. Mercury isotopes in the Hg-enriched sediments were characterized by near-zero Δ199Hg values, which is consistent with volcanism acting as the primary source of Hg to the sediments. Spectral analysis of the Hg/TOC ratio showed significant periodicity at ~100 kyr and ~ 23 kyr as well as a weaker signal at ~41 kyr consistent with Milankovitch cycles. A cross spectral analysis of Hg/TOC and the LR04 δ18O stack record suggests that the peak in volcanism lags the temperature minimum by ~6 kyr, and occurs prior to the δ18O minimum known as the glacial termination by ~14 ± 2 kyr. The records of volcanic activity in this site are also consistent with a prominent rise in atmospheric CO2 and negative excursion of benthic carbon isotopes throughout the MPT. This study provides direct sedimentary evidence in the TWP of the feedback between volcanic activity, climate change and atmospheric CO2.

Integrated thermodynamic and thermomechanical numerical modeling: A useful method for studying deep Earth water and carbon cycling

The plate tectonic evolution controls the mass and energy circulation between the Earth's surface and interior, during which the volatiles (e.g., water and carbon) could also accompany the tectonic up- and down-wellings. The deep Earth injection of volatiles (ingassing mainly via subduction) can modify the physical and chemical properties of rocks and thus strongly affect the processes and dynamics of Earth's interior. On the other hand, the emission of volatiles to the Earth's surface (outgassing mainly through volcanism and rifting) can influence the evolution of atmosphere, climate and habitability. Thus, the deep water and carbon cycling plays important roles in not only the solid Earth dynamics, but also the surficial environments. The time-dependent evolution of deep Earth condition and large-scale plate tectonic reconstruction have generally been used to infer the fluxes and pathways of water and carbon cycling, as well as the resulting ocean water and atmospheric carbon evolution in the Earth's surficial reservoirs. Besides multiple observations and experiments, the integrated thermodynamic and thermomechanical numerical modeling provides as a useful way for studying deep Earth water and carbon cycling in variable tectonic settings and with different conditions. In the review, I firstly introduce the numerical method integrating thermodynamic data into thermomechanical principles. Then, several typical numerical models are introduced, which highlight, respectively, the (de)hydration in shallow lithospheric subduction channel, the deep water cycling in the upper mantle and transition zone, as well as the subduction-induced carbon cycling. Finally, the general issues about water and carbon fluxes between the Earth's interior and surface are discussed, which are less constrained issues and require further studies with possible contributions from the integrated thermodynamic and thermomechanical numerical modeling.

Oxidation Extent of the Upper Mantle by Subducted Slab and Possible Oxygen Budget in Deep Earth Inferred From Redox Kinetics of Olivine

AbstractRedox input by subducted slab into mantle is important for deep cycle and isotopic evolution of volatile elements, whose stable forms are controlled by redox state. Given reduced condition in lower part of the upper mantle, taking redox budget from lithospheric mantle into consideration is crucial in redefining redox state there. To constrain to which extent subducted slab modified redox state of the uppermost mantle and how much oxygen budget slab carried into deep Earth, we investigated redox kinetics of olivine adopting diffusion couple method at 1 GPa and 1,373–1573 K in a piston cylinder apparatus. It is found that redox process in olivine is diffusion‐controlled, and diffusing on the order of 10−12 m2/s at 1473 K. Oxidation process in reduced part is oxygen fugacity (fO2)‐independent with activation enthalpy of 235 ± 56 kJ/mol, while reduction process in oxidized part is fO2‐dependent with an fO2 exponent of 2/5. Diffusion profile analysis reveals that for magnetite‐free couple, redox process is controlled by oxygen grain boundary diffusion (GBD) below ΔFMQ + 1, and rate‐limited by faster species which might be hydrogen related Mg vacancy above ΔFMQ + 1. However, for magnetite‐bearing couple, oxygen GBD dominates redox process across wide fO2 range. The extremely slow rate limits the homogenization of the slab with surrounding mantle so that redox state of the uppermost mantle remains unchanged in the past 3.5 Gyrs. A highly underestimated oxygen reservoir may have formed in deep Earth, when subducted slab transports oxidized components to region deeper than the mantle transition zone.

Sediments, Serpentinites, and Subduction: Halogen Recycling from the Surface to the Deep Earth

Halogens are important elements that participate in a variety of biogeo-chemical processes and influence the solubility of metals in subduction-zone fluids. Halogens are powerful tracers of subducted volatiles in the Earth’s mantle because they have high abundances in seawater, sediments, and altered oceanic lithosphere but low concentrations in the mantle. Additionally, Br/Cl and I/Cl ratios, as well as Cl-isotope ratios, have characteristic ranges in different surface reservoirs that are not easily fractionated in the mantle. Current data suggest that subduction of serpentinised lithosphere is a major source of halogens in the Earth’s mantle.

High Temperature Melting Curve of Basaltic Glass by Laser Flash Heating

Basalt is an igneous rock originating from the cooling and solidification of magma and covers approximately 70% of Earth’s surface. Basaltic glass melting in the deep Earth is a fundamental subject of research for understanding geophysics, geochemistry, and geodynamic processes. In this study, we design a laser flash heating system using two-dimensional, four-color multi-wavelength imaging radiometry to measure the basaltic glass melting temperature under high pressure conditions in diamond anvil cells. Our experiment not only determines the temperature at the center of heating but also constructs a temperature distribution map for the surface heating area, and enables us to assess the temperature gradient. Through precise temperature measurements, we observe that the basaltic glass melting temperature is higher than those in previous reports, which is near the normal upper-mantle isotherm, approaching the hot geotherm. This suggests that basalt should not melt in most of the normal upper mantle and the basaltic melts could exist in some hot regions.

Some Remarks on the Electrical Conductivity of Hydrous Silicate Minerals in the Earth Crust, Upper Mantle and Subduction Zone at High Temperatures and High Pressures

As a dominant water carrier, hydrous silicate minerals and rocks are widespread throughout the representative regions of the mid-lower crust, upper mantle, and subduction zone of the deep Earth interior. Owing to the high sensitivity of electrical conductivity on the variation of water content, high-pressure laboratory-based electrical characterizations for hydrous silicate minerals and rocks have been paid more attention to by many researchers. With the improvement and development of experimental technique and measurement method for electrical conductivity, there are many related results to be reported on the electrical conductivity of hydrous silicate minerals and rocks at high-temperature and high-pressure conditions in the last several years. In this review paper, we concentrated on some recently reported electrical conductivity results for four typical hydrous silicate minerals (e.g., hydrous Ti-bearing olivine, epidote, amphibole, and kaolinite) investigated by the multi-anvil press and diamond anvil cell under conditions of high temperatures and pressures. Particularly, four potential influence factors including titanium-bearing content, dehydration effect, oxidation−dehydrogenation effect, and structural phase transition on the high-pressure electrical conductivity of these hydrous silicate minerals are deeply explored. Finally, some comprehensive remarks on the possible future research aspects are discussed in detail.

Ultrahigh-Pressure Magnesium Hydrosilicates as Reservoirs of Water in Early Earth.

The origin of water on the Earth is a long-standing mystery, requiring a comprehensive search for hydrous compounds, stable at conditions of the deep Earth and made of Earth-abundant elements. Previous studies usually focused on the current range of pressure-temperature conditions in the Earth's mantle and ignored a possible difference in the past, such as the stage of the core-mantle separation. Here, using abinitio evolutionary structure prediction, we find that only two magnesium hydrosilicate phases are stable at megabar pressures, α-Mg_{2}SiO_{5}H_{2} and β-Mg_{2}SiO_{5}H_{2}, stable at 262-338GPa and >338 GPa, respectively (all these pressures now lie within the Earth's iron core). Both are superionic conductors with quasi-one-dimensional proton diffusion at relevant conditions. In the first 30 million years of Earth's history, before the Earth's core was formed, these must have existed in the Earth, hosting much of Earth's water. As dense iron alloys segregated to form the Earth's core, Mg_{2}SiO_{5}H_{2} phases decomposed and released water. Thus, now-extinct Mg_{2}SiO_{5}H_{2} phases have likely contributed in a major way to the evolution of our planet.

Partitioning of noble gases (He, Ne, Ar, Kr, Xe) during Earth’s core segregation: A possible core reservoir for primordial noble gases

Noble gas isotopes in plume-influenced oceanic-island basalts (OIBs) clearly indicate the existence of distinct reservoirs somewhere in the deep Earth that are characterized by their more primitive noble gas isotopic signatures. As one of the largest differentiated layers on Earth, whether the Earth’s liquid outer core can preserve ‘primordial’ noble gases is fundamental for better understanding the Earth’s formation and the mantle evolution. Since Earth’s core is believed to have formed via liquid iron segregated from magma ocean during the planetary accretion stage, how much noble gases could have been incorporated into Earth’s core depends on the partitioning of noble gases between liquid metal and molten silicates. In this study, we perform thermodynamic integration (TI) calculations based on first-principles molecular dynamics (FPMD) simulation to investigate the partition coefficients of noble gases (NG: He, Ne, Ar, Kr, Xe) between liquid Fe and MgSiO3 melt. The simulations have been performed by adopting conditions that the pressures are from 10 ∼ 135 GPa and the temperatures from 2300 ∼ 5000 K to fully account for possible core-mantle equilibrium conditions. By analyzing the temperature and pressure dependence of the results, we suggest that the metal-silicate partitioning of noble gases (DNG) merely depends on the temperature, with extremely low DNG < 0.001 at temperatures < 2500 K (20 GPa), but increases to different degrees at high temperatures. The DNG tends to be more affected by temperature as the noble gas atomic mass increases, with the least temperature effect on the partition coefficient of He (DHe), which increases from ∼ 10−3 at 2300 K (10 GPa) to ∼ 10−1 (5000 K, 135 GPa) near the core-mantle boundary (CMB), and DNe = 10−6 ∼ 10−3, DAr = 10−6 ∼ 10−2, DKr = 10−7 ∼ 10−1 and DXe = 10−5 ∼ 100 from 2300 to 5000 K, respectively. Analysis of electronic interactions indicates that noble gases have positive chemical bonding with Fe, Mg, and Si atoms, and the bonding strengths increase with pressure as well as increasing noble gas atomic mass. Based on our calculated partition coefficients, we suggest that Earth’s core may have preserved significant amounts of noble gases considering the volatile-rich environment from which the core segregated.

Redox heterogeneity of picritic lavas with respect to their mantle sources in the Emeishan large igneous province

The oxygen fugacity (fO2) of the Earth’s mantle is a key parameter that regulates fundamental geological processes such as planetary differentiation, mantle melting, and volatile cycling. Large igneous provinces (LIPs) are among the most voluminous mafic volcanic eruptions in the Earth’s history. Constraining the fO2 of LIP rocks is critical for understanding the redox state of the mantle and migration of volatiles from the deep Earth to the atmosphere. Here, we investigated primitive picrites from the Dali and Lijiang areas belonging to the Emeishan LIP, which contain early-crystallized olivine phenocrysts with Fo contents up to 93.5 and 91.9, respectively. The fO2 conditions of primary and derivative melts are determined by the olivine-spinel and olivine-melt V oxybarometers, aided by temperature estimates from olivine-spinel Al and olivine-melt Sc/Y thermometers. The calculated fO2 values are negatively correlated with olivine Fo contents due to fractionation of mafic minerals in a system closed to oxygen. The fO2s of Dali and Lijiang primary melts are −0.8 ± 0.4 and + 0.6 ± 0.3 (1σ) ΔFMQ log units, respectively, more variable than those of primitive MORBs, indicating significant fO2 fluctuations in primary magmas from the Emeishan LIP caused by changes in both redox state of the source rock and depth of melt extraction. Melt barometer constrains the Dali and Lijiang primary melts generated at 4.7 and 3.0 GPa, respectively. After correcting for the depth effect, the Dali and Lijiang sources are more oxidized (with higher Fe3+/∑Fe ratios), in varying degrees, than the ambient upper mantle, likely due to incorporation of recycled surface materials. Under such oxidized conditions, mantle carbon is efficiently extracted during melting in the form of CO2 and released to the atmosphere during massive magma emplacement, which may have played an important role in causing the climatic and environmental changes and triggering the end-Guadalupian mass extinction.

Preface to the Special Issue “Deep fluid: Large Scale Water Circulation Connecting Surface and Interior of Earth”, as a Counterpart of Joint Special Volumes “At the Cutting Edge of Hot Spring Studies: Understanding the Water Cycle in the Lithosphere and the Deep Earth” of Chikyukagaku (Geochemistry) and Journal of Geography (Chigaku Zasshi)

Preface to the Special Issue “Deep fluid: Large Scale Water Circulation Connecting Surface and Interior of Earth”, as a Counterpart of Joint Special Volumes “At the Cutting Edge of Hot Spring Studies: Understanding the Water Cycle in the Lithosphere and the Deep Earth” of Chikyukagaku (Geochemistry) and Journal of Geography (Chigaku Zasshi)

3-D Inversion of Z-Axis Tipper Electromagnetic Data Using Finite-Element Method With Unstructured Tetrahedral Grids

<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Z$ </tex-math></inline-formula> -axis tipper electromagnetic (ZTEM) technique is an airborne electromagnetic method that detects anomalies in the deep earth that are induced by natural sources. Conventional ZTEM forward modeling is generally conducted using structured grids that have limited accuracy and cannot be used to invert complex underground structures and topography. However, unstructured grids can accurately model complex underground structures with fewer cells. Therefore, to effectively model and recover the complex underground structures, we developed a 3-D framework with unstructured tetrahedral grids for ZTEM forward modeling and inversions. The forward problem was formulated using the finite-element method with unstructured tetrahedral grids. To solve the inverse problem, we used a limited-memory quasi-Newton algorithm (L-BFGS) with a parallel direct solver for optimization in order to avoid the explicit calculation of the Hessian matrix and save the memory and computational time. To validate our forward and inversion algorithms, we conducted numerical experiments on three synthetic models and inverted a survey dataset acquired for a tunnel project in Tibet, China. The experimental results demonstrate the effectiveness of our unstructured finite-element and L-BFGS method for modeling and inverting ZTEM data.

Development Strategy of Quantum-Based Deep Geophysical Exploration Technology and Equipment

Quantum-based sensing and measurement technology is a disruptive technology that can realize fine detection of the gravity and magnetic fields in deep Earth, and it has become a key development direction for geophysical exploration equipment worldwide. This study focuses on the frontier technologies for the quantum-based high-precision measurement of Earth’s gravity and magnetic fields, summarizes the development status of quantum-based geophysical exploration equipment, and analyzes demand for the superconducting quantum-based electromagnetic detection system, magnetic vector gradient detection system, superconducting gravity detection system, and cold-atom absolute-gravity exploration system during deep resource exploration. Moreover, the international trend of quantum-based high-precision measurement technology as well as the development opportunities and challenges in this field are analyzed. To improve the core technology research, complete localization, and exploration application of quantum-based geophysical exploration equipment in China, we propose the development goals, technical system, key tasks, and strategic planning for a new generation of quantum-based high-precision deep geophysical exploration equipment. This aims to achieve breakthroughs in superconducting quantum chips and high-sensitivity sensors, establish a collaboration model for the independent development of China’s quantum-based geophysical exploration equipment, promote the high-quality development of deep exploration equipment, and provide strategic support for solving major problems associated with deep mineral resource exploration and revealing of Earth’s deep structure.

Magnetic Sensing System for Potential Applications in Deep Earth Extremes for Long-Term Continuous Monitoring

Long-term monitoring of weak changes in the magnetic field in the deep part of the Earth, allows to detect anomalies related to the pre-natural disaster stage at the onset of the deformation of the earth’s crust. However, standard electronic instruments are unable to work under high temperatures and high-pressure harsh environments for a long time. To address this problem, an in-well magnetic field measurement system, including a three-axis “residence times difference” fluxgate magnetometer, a heat exchange system with a coolant, and a control module, is designed. The measured maximum sensor sensitivity at room temperature is 0.02 s/(A/m). The rms input noise is within ±2 nT, corresponding to a noise spectral density of 200 pT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> @1 Hz, that is sufficient to accurately detect the fluctuations of the geomagnetic field. The feasibility of the system was verified in laboratory at four temperatures, from 120°C to 210°C, corresponding to 2000 m - 5000m subsurface depths. When, in the experiments performed at 210 °C, the magnetic field was changed of some hundreds of nT, the sensor outputs responded very well in the three directions, with a dynamic detectability of few tens of nT. The control module maintains the internal temperature in the range 25 °C - 40 °C when the external temperature varies between 120 °C and 210°C, allowing a good long-term stability, as demonstrated by aging tests in laboratory. Finally, field experiments were conducted to verify the engineering feasibility of the system for ten days at 100 m depth and 15~18 °C.

Domain Knowledge Powered Two-Stream Deep Network for Few-Shot SAR Vehicle Recognition

Synthetic aperture radar (SAR) target recognition faces the challenge that there are very little labeled data. Although few-shot learning methods are developed to extract more information from a small amount of labeled data to avoid overfitting problems, recent few-shot or limited-data SAR target recognition algorithms overlook the unique SAR imaging mechanism. Domain knowledge-powered two-stream deep network (DKTS-N) is proposed in this study, which incorporates SAR domain knowledge related to the azimuth angle, the amplitude, and the phase data of vehicles, making it a pioneering work in few-shot SAR vehicle recognition. The two-stream deep network, extracting the features of the entire image and image patches, is proposed for more effective use of the SAR domain knowledge. To measure the structural information distance between the global and local features of vehicles, the deep Earth mover’s distance is improved to cope with the features from a two-stream deep network. Considering the sensitivity of the azimuth angle in SAR vehicle recognition, the nearest neighbor classifier replaces the structured fully connected layer for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> -shot classification. All experiments are conducted under the configuration that the SARSIM and the Moving and Stationary Target Acquisition and Recognition (MSTAR) dataset work as a source and target task, respectively. Our proposed DKTS-N achieved 49.26% and 96.15% under ten-way one-shot and ten-way 25-shot, whose labeled samples are randomly selected from the training set. In standard operating condition (SOC) as well as three extended operating conditions (EOCs), DKTS-N demonstrated overwhelming advantages in accuracy and time consumption compared with other few-shot learning methods in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> -shot recognition tasks.

Integral assessment of the geodynamic conditions for the formation of the Black Sea basin and connection with the current regime of groundwater in its northwestern shelf

The paper has a multidisciplinary character connecting bathymetric, geophysical and geological information to innovatively reconstruct the geodynamic conditions of the Black Sea basin formation, their influence on the modern relief and groundwater regime within its northwestern shelf as a reference region. The major goal is the rationale of modern geodynamic settings for the Black Sea Basin against the back- ground of the processes of its closure under tangential compression conditions, as well as their relation- ship with the hydrogeological conditions of the shelf zone. As primary evidence, the author determined the spatial positions of the Constanta-Sinop and SubPontian Suture Zones, pinpointing absorption locations of the Earth's crust at subduction zones. The facts and arguments presented in this paper are well integrated into the scheme of the oncoming of the Pontides island arc to the Eurasian Plate and the gradual closure of the back-arc marginal Black Sea Basin with a crust of transitional-type crust. The specific feature of the study is an innovative approach to comprehensive analysis of data that are a result of geological and geophysical works within the Black Sea water area. In doing so, major attention is paid to the spatial morphostructural analysis and interpretation of newly integrated digital data array, as a result of bathymetric surveys, namely the EMODnet 2019—2022. The subject of analysis is the basic structural surfaces, including the Modern and on its margin consolidated basement. New justification is formulated on the confinement of gas seeps and mud volcanoes, within the Black Sea Basin, to the deep earth`s crust structures. The graphical correlation of the mentioned ones is performed as well as their spatial position in the structural-geodynamic model of the region is theoretically substantiated. A generalized geomorphological zoning of the northwestern shelf of the Black Sea with the identification of the Dobrogea, Odesa and Kalamit zone is proposed. Within the Odesa geomorphological region, an integrated geological and geomorphological analysis was carried out and, as a result, dividing the shelf into submarine groundwater discharge (SGD) zone of aquifer was substantiated. The study, carried out by the author is of crucial importance to understanding the tectonic and geo- dynamic characteristics of the Black Sea Basin as well as for forecasting SGD zones and fresh groundwater resources. It is recommended to set targeted prospecting works to assess fresh groundwater resources in order to meet the water needs of coastal communities.