Anomalous Field Research Articles

Long-term persistency of a strong non-dipole field in the South Atlantic

Earth’s magnetic field exhibits a dominant dipole morphology. Notwithstanding, significant deviations from the dipole are evident today, particularly the South Atlantic Anomaly (SAA), characterized by anomalously low-field intensity and high directional variability, diminishing the field’s shielding effect. To assess the persistence of SAA-like features over multimillion-year scales, we combine paleomagnetic data from Trindade Island (20°30’S, 29°22’W) with an evaluation of paleosecular variation (PSV) over the past 10 Myr. We employ synthetic models to explore how the position and intensity of magnetic flux patches at the core-mantle boundary can influence the long-term field behavior. Here we present results that reveal anomalous field signatures in the South Atlantic and the Atlantic-Pacific hemispheric asymmetries are enduring features, likely linked to a bottom-up control of PSV by the inner core’s heterogeneities but with contributions from mantle anomalies in the long-time range.

The Generation of Seismogenic Anomalous Electric Fields in the Lower Atmosphere, and Its Application to Very-High-Frequency and Very-Low-Frequency/Low-Frequency Emissions: A Review

The purpose of this paper is, first of all, to review the previous works on the seismic (or earthquake (EQ)-related) direct current (DC) (or quasi-stationary) electric fields in the lower atmosphere, which is likely to be generated by the conductivity current flowing in the closed atmosphere–ionosphere electric circuit during the preparation phase of an EQ. The current source is electromotive force (EMF) caused by upward convective transport and the gravitational sedimentation of radon and charged aerosols injected into the atmosphere by soil gasses during the course of the intensification of seismic processes. The theoretical calculations predict that pre-EQ DC electric field enhancement in the atmosphere can reach the breakdown value at the altitudes 2–6 km, suggesting the generation of a peculiar seismic-related thundercloud. Then, we propose to apply this theoretical inference to the observational results of seismogenic VHF (very high frequency) and VLF/LF (very low frequency/low frequency) natural radio emissions. The formation of such a peculiar layer initiates numerous chaotic electrical discharges within this region, leading to the generation of VHF electromagnetic radiation. Earlier works on VHF seismogenic radiation performed in Greece have been compared with the theoretical estimates, and showed a good agreement in the frequency range and intensity. The same idea can also be applied, for the first time, to seismogenic VLF/LF lightning discharges, which is completely the same mechanism with conventional cloud-to-ground lightning discharges. In fact, such seismogenic VLF/LF lightning discharges have been observed to appear before an EQ. So, we conclude in this review that both seismogenic VHF radiation and VLF/LF lightning discharges are regarded as indirect evidence of the generation of anomalous electric fields in the lowest atmosphere due to the emanation of radioactive radon and charged aerosols during the preparation phase of EQs. Finally, we have addressed the most fundamental issue of whether VHF and VLF/LF radiation reported in earlier works is either of atmospheric origin (as proposed in this paper) or of lithospheric origin as the result of microfracturing in the EQ fault region, which has long been hypothesized. This paper will raise a question regarding this hypothesis of lithospheric origin by proposing an alternative atmospheric origin outlined in this review. Also, the data on seismogenic electromagnetic radiation and its inference on perturbations in the lower atmosphere will be suggested to be extensively integrated in future lithosphere–atmosphere–ionosphere coupling (LAIC) studies.

Строение центральной части палеопротерозойского Лосевского террейна по данным плотностного моделирования

The results of detailed three-dimensional density modeling of the upper crust of the central part of the Losevsky terrane located in the northern part of the Voronezh crystal massif are considered. The distribution of absolute crustal density values of to a depth of 16 km was obtained as a result of the inversion of local anomalies of the gravitational field in the Bouguer reduction. The solution of the inverse problem of gravimetry was implemented within the framework of the initial model, which was formed using digital geological and geophysical data from the study area: the regional density model of the East European Platform lithosphere and its corresponding regional gravity field; the field of local gravity anomalies, representing the difference between the observed and regional fields of the lithosphere model; generalized information on the density of sedimentary cover rocks and the crystal basement; the thickness scheme of the «gravity-active» layer, obtained on the basis of statistical analysis of the anomalous field; geological and topographic information. Quantitative interpretation of the gravimetry data allowed us to obtain fundamentally new information about the geological structure of the upper crust of the study area. The reliability of the obtained results is confirmed by the consistency of a priori data and the correspondence of the total model (local plus regional) and observed gravitational fields.

The Aerogeophysical Atlas of Tocantins State: Synthesis of Magnetic Anomaly And Radioelement Maps With Emphasis on Regional Signatures and the Serra Da Cangalha Impact Structure

The Tocantins State Aerogeophysical Atlas (TSAA) is an institutional product of the Geological Survey of Brazil. It is aimed at promoting the use of airborne magnetic and gamma-ray spectrometry data to support geophysical and geological research at state level. Here, we present a synthesis of the TSAA with special emphasis on the interpretation of the magnetic (Anomalous Magnetic Field, First Vertical Derivative (FVD), and Total Gradient Amplitude (TGA) images) and radiometric (RGB composite color map of concentrations, Inverse Images of K, eTh, and eU, and Normalized eU enhancement) map. In particular, the radiometric data for the Serra da Cangalha impact structure in northeast Tocantins are discussed. For Tocantins State, the results show that the radiometric and/or magnetic signatures of geological units (e.g., Mosquito Formation basalts; granite-gneiss/migmatite terrains) and structural features (e.g., dykes and lineaments), or related exogenous deposits (Serra Geral do Tocantins quartzose soils; alluvial deposits of main drainage channels) can be visualized well on regional-scale maps. Analysis of radiometric ratios for the area of the Serra da Cangalha impact structure indicates that eU concentrations are enriched in the annular basin around the central uplift structure, and in the zone straddling the contact between the Piauí and Pedra de Fogo formations. In the latter case, the elevated eU concentrations could be related to brecciated chert layers or silicified sandstones.

Кластерный анализ геофизических полей при тектоническом районировании Африкано-Антарктического сектора Южного океана

The tectonic zoning of the African-Antarctic sector of the Southern Ocean was carried out on the basis of cluster analysis of a large volume of heterogeneous geophysical and geological data. It is known that the degree of geological and geophysical exploration of this part of the ocean by marine surveys and drilling remains extremely low. The results of such an analysis make it possible in areas with weak geophysical knowledge to quickly draw up tectonic zoning schemes based on regional geophysical data that are freely available throughout the entire territory of the world ocean and use them as a basis for further interpretation. The following materials were used as input data or classification features: ocean floor topography, gravity anomalies in free air and in the Bouger reduction, ∆Ta anomalous magnetic field model, ocean floor age, geoid height data, and the SL2013sv seismotomography model. «K-means» algorithms and the «Gaussian mixtures» method used for clustering. Based on the results of the application of these algorithms, cluster models of the study region were obtained, in which the selected classes fully reflect the main tectonic elements.

Розробка цифрових карт модуля індукції геомагнітного поля для території України

Knowledge of Ukraine`s geomagnetic field is based on magnetic surveys of the geomagnetic field induction module B and its power and angular components, as well as on observations or calculations of their anomalous values. The article describes the methods for constructing a digital map of the induction module of the geomagnetic field B. The map of module B for the epoch of 1969.5 is developed, which is the ground to create the maps of module B and its anomalies ΔB for an arbitrary epoch. The results of the ground absolute magnetic survey of 1969-1972, the analytical model of the main geomagnetic field BIGRF, as well as the map of the anomalous magnetic field on a scale of 1: 1,000,000 were used to construct the map of the geomagnetic field induction module B. The digital map of the module and anomalies of the geomagnetic field induction module B for the 1969.5 epoch was obtained by calculating the correction based on their difference values at the points of the absolute reference network. It was spread by interpolation according to the 1x1km matrix to the entire data array for the territory of Ukraine. The geomagnetic field induction module B for the 2005.5 epoch was calculated by adding to its values in the 1969.5 epoch the calculated values of the field dynamics ВIGRF and the "magnetizing" effect of anomalies of the induction module ΔΔB. The developed map is an approximate representation of the magnetic field modulus, since the amount of remanent magnetization was not taken into account during the calculation, which may cause minor deviations of the calculated and observed field values. The induction module of the geomagnetic field B in the epoch of 1969.5 varies in the range of 46,500÷62,000 nT, and in the epoch of 2005.5 ‒ 47,000÷63000 nT, increasing from the southwest to the northeast of the territory of Ukraine. Its maximum values are observed in the areas of regional and local magnetic anomalies, in particular in the area of the Kryvyi Rih-Kremenchuk anomalous strip and the southeastern edge of the Kursk anomaly. The dynamics of the BIGRF field for the period of 1969.5÷2005.5 is characterized by values from 700 nT in the east of the territory of Ukraine to 950 nT in the west, and the magnitude of the magnetizing effect ΔΔB varies within ±10 nT, reaching maximum values (up to 100-190 nT) in the regions of intense magnetic anomalies. The digital map of the geomagnetic field induction module B, developed in 2005.5, has been verified. This was done by measuring the values of module B in the magnetic observatories of Kyiv, L’viv, and Odesa, as well as in the Repeat Stations of the Ist and IInd classes. The results showed that there was only a small difference (-20 ÷ 40 nT) between the calculated and measured values of modulus B. Their most significant differences are spatially correlated with areas of modern activation of the Earth's crust on the territory of Ukraine and electrical conductivity anomalies.

Polarity in Liquid Crystals Formed by Self-Assembled Umbrella-Shaped Subphthalocyanine Mesogens.

We investigated the properties of p-type semiconducting columnar phases in self-assembled umbrella-shaped mesogens that have subphthalocyanine cores and oligo-thienyl arms. These compounds have nonswitchable phases that exhibit remanent electric polarization and nonlinear optical activity. Additionally, these compounds can generate photocurrents in the visible spectral range due to their wide absorption band. The photocurrent can be significantly increased by doping materials with fullerene. The charge mobility shows an anomalous field dependence, which decreases with the temperature.

Hybrid multilayer perceptron and convolutional neural network model to predict extreme regional precipitation dominated by the large-scale atmospheric circulation

Recent advances in deep learning have provided tools that enable meteorologists to predict extreme precipitation using massive atmospheric data. However, individual models are constrained by imbalanced samples and prone to false alarms owing to the rarity of extreme precipitation events. In this study, a novel ensemble learning model, that is, hybrid multilayer perceptron and convolutional neural network (MLP-CNN) model is proposed for the binary prediction of extreme precipitation in Central-Eastern China (CEC), with a daily time horizon. The MLP-CNN model achieves an overall accuracy of 86% in predicting extreme and non-extreme precipitation days using the anomalous fields of two large-scale atmospheric predictors, i.e., geopotential height at 500 hPa and vertically integrated water vapor transport. Subsequently, we employ the MLP-CNN to predict extreme precipitation with a 1–15 day leadtime. The performance of MLP-CNN tends to decrease with increasing leading time of circulation anomalies. However, 1–2 days of advance forecasting can be considered a reference for predicting the occurrence probabilities of extreme precipitation. Finally, based on various evaluation metrics, MLP-CNN outperforms the independent predictions from MLP, CNN, and two other machine learning models (i.e., random forest and support vector machine). Overall, in scenarios where samples are limited, the utilization of hybrid models presents an opportunity for optimizing predictions for extreme precipitation.

Spatio-temporal characteristics of seismic strain anomalies reveal seismic risk zones along the Longmenshan fault zone and adjacent areas

Introduction: Identifying and quantifying earthquake precursors, and analyzing their physical mechanisms, continues to be a challenge for earthquake forecasting. In this study, orthogonal functions were developed to effectively identify precursor anomalies, thereby improving the forecasting of strong earthquakes.Methods: To study the spatio-temporal contour anomalies in seismic strain fields, we assessed them for seismic activity variables and natural orthogonal function expansion, in six strong earthquakes near the Longmenshan Fault Zone, China, that have occurred since 2008.Results: We observed that, prior to these earthquakes, the temporal factor (the time variation characteristics of the strain field) displayed anomalies with high/low values exceeding the mean square error within a stable context. The anomalies exhibited multi-component characteristics and were primarily concentrated in the first four-strain fields. Short-term and impending-earthquake anomalies were observed in the temporal factor before the 2008 Wenchuan (M8.0) and 2013 Lushan (M7.0) earthquakes, while medium-term and long-term anomalies appeared before the other four strong earthquakes, without notable short-term anomalies. The temporal evolution of strain field contour anomalies, and the strain contours positive and negative intersection, showed that central areas surrounded by multiple strain field contour anomalies were potential locations for strong earthquakes. This suggests a potential approach for earthquake location forecasting. Since 2009, there have been five strong earthquakes, each affected to varying degrees by anomalous strain fields from the 2008 Wenchuan (M8.0) earthquake.Conclusion: The results of this study corroborate the findings of the focal mechanism’s node shear stress, indicating significant physical implications of the anomalies and the reliability of these conclusion.

INFRARED THERMAL IMAGING CONTROL OF RADIATION DERMATITIS DYNAMICS.

Radiation-induced dermatitis impairs the quality of life of cancer patients and may lead to the need of interrupting radiotherapy. The grade of dermatitis is subjectively assessed by the visual examination. There is an urgent need for both objective and quantitative methods for assessing the current grade of dermatitis and predicting its severity at an early stage of radiotherapy. The aim of the study was to evaluate the advantages and limitations of infrared thermography for monitoring the current level of radiation-induced dermatitis and predicting its severity by quantitative analysis of the thermal field dynamics in the irradiated zone. 30 adult patients were examined by infrared thermography during the course of 2D conventional radiotherapy for malignant tumors of various types and localizations. Our approach for quantifying the thermal field caused by dermatitis alone was applied. A statistical (correlation and ROC) analysis was performed. Dermatitis of varying severity was observed in 100% of the patients studied. The dynamics in the intensity of the anomalous thermal fields in the irradiated zone correlated with the dynamics of dermatitis grades, excluding the case of a radiosensitive tumor (correlation coefficient 0.74÷0.84). It was found that the maximum toxicity (dermatitis grade ≥ 3) develops in patients who how significant hyperthermia in the area of interest (≥ 0.7 °C) at an early stage of radiotherapy. The ROC analysis demonstrated the "good quality" of the prognosis method (AUC = 0.871). The non-invasive and cheap infrared thermography is a suitable tool for objective quantitative monitoring the current dermatitis grade during radiotherapy as well as predicting its severity for any tumor location.

An experimental investigation on the discrete Poisson’s upward continuation of anomalous gravity field data

An experimental investigation on the discrete Poisson’s upward continuation of anomalous gravity field data

For the Classification of Anomalous Geophysical Fields that Existed Prior to an Earthquake

The consolidated paper presents work carried out in the sphere of earthquake problems. On the base of theoretical and experimental studies, it is shown earthquake prediction possibility. There are discussed earthquake indicators and triggering exogenous factors in the example of the Caucasus region. Because the earthquake preparation process causes anomalous changes with complex characteristics in various geophysical fields, it is given scientifically proven suggestions for the classification of these fields as earthquake precursors, indicators, and triggering factors. It offers a short-term plan for future work in the earthquake prediction direction.

Quantification and suppression of optical non-orthogonality and light intensity noise in all-optical hot atomic sensing systems

All-optical hot atomic sensing systems such as optical pumping magnetometers (OPM) and comagnetometers, nuclear magnetic resonance (NMR) magnetometers and gyroscopes, have the ability to sense magnetic field, anomalous field and inertial rotation, thus having a wide potential for applications in precision measurement, fundamental physics research and inertial navigation. System noise limits the minimum value of the signal that can be measured and there is coupling effect between the noises. Therefore, the quantification and suppression of various noise are challenging and should be investigated. As one of the major noises, the light intensity fluctuation of the probe light and the pump light affects the sensitivity of the all-optical hot atomic sensing systems. However, there has been no in-depth research on the quantification of the light intensity noise. In this paper, a method of measuring the light intensity noise is proposed, which can be applied to kinds of all-optical hot atomic sensing systems. For verification, the effects of probe and pump light intensity fluctuations on system noise are simulated and experimentally verified in a spin exchange relaxation free (SERF) comagnetometer. Besides, it is found that the optical non-orthogonality amplifies the probe light intensity noise by more than 3.4 times and a quantification method of optical non-orthogonality is proposed. Finally, a suppression method of the light intensity noise is presented by suppressing the optical non-orthogonality and the noise is suppressed by 59%. A universal light intensity noise quantification method is proposed for all-optical hot atomic sensing systems, and a light intensity noise suppression method is proposed for SERF comagnetometers, which can be applied to the suppression of noises coupled with atomic polarization.

УДОСКОНАЛЕНА МЕТОДИКА ДЕТАЛЬНОЇ МАГНІТНОЇ ЗЙОМКИ ДЛЯ ВИРІШЕННЯ ЗАВДАНЬ НАФТОГАЗОВОЇ ГЕОЛОГІЇ

Background. Nowadays, interest in studying the local anomalous magnetic field to solve the problems of oil and gas geology is growing, and the capabilities of the equipment can significantly increase the speed, accuracy and detail of work. Accordingly, the development and testing of an improved method of detailed magnetic recording in motion becomes relevant. Methods. For areas with low gradient magnetic field, we assessed the accuracy of the survey by comparing the maps obtained from repeated surveys of the site. Results. The survey of the magnetic field was conducted in the movement. The total surveyed area was about 20 square kilometers in the Zinkovsky district of the Poltava region. The inter-profile distance was about 50 meters, the distance between the points of observation on the profile was about 1 meter. This grid of observations allows us to get maps that differ significantly from the maps obtained by the usual density of observations. This technique also allows identifying local anomalies, and drawing conclusions about the fine structure of the magnetic field. The main objects that form anomalies and their geological characteristics are identified. On this basis, interpreted magnetic field anomalies in oil and gas regions were catalogued. Conclusions. We have proposed explanation of tectonic and geochemical factors, which form local anomalies of the magnetic field of the studied areas. Three types of anomalies associated with ravines are distinguished. Positive anomalies over ravines and step-type anomalies, in our opinion, are associated with tectonic movements, and negative anomalies are due to slope wash processes. Alternating magnetic fields in the studied areas may be due to ferruginized deposits.

Gravity modeling of ore gabbroids Korsun-Novomirhorod pluton

This work concerned three-dimensional gravity modeling of the Gorodishche gabbro-anorthosite massif located within the Korsun-Novomirgorod pluton of the Ukrainian Shield. A three-dimensional model of the upper crust was created using maps of the anomalous gravitational field at a scale of 1:200 000, taking into account data from seismic methods of various modifications. The differences in the structure of the intrusive complex and its gneisses were reflected in seismic wave fields, allowing us to determine the boundaries of the entire intrusive massif: rapakivi granites and basic rocks. Three-dimensional gravity was modeled to separate these complexes of different densities. This made it possible to identify gabbro-anorthosite bodies with a maximum thickness of 5 km in the upper part of the section, and to study the contacts of the intrusive complex and gneisses. In the process of solving inverse problems, various criteria for local optimization of gravitational field sources were implemented. In the iterative process, three different functionals were calculated. The mean square of the difference between the observed and theoretical fields is F1, the average sum of the moduli of the field difference is the functional F2, and the preliminary logarithm of the parameters is the functional F3. The joint use of functionals makes it possible to reduce various types of noise in the observed potential field data. In the process of research, it was found that the use of functionals of various types in the selection method algorithms is quite advisable. This makes it possible to create new algorithms that improve feasible solutions to the inverse problem, which is necessary for the implementation of additive technologies for the quantitative interpretation of gravity survey data. The constructed model, which takes into account all available a priori information about the density and geometric parameters of anome-forming objects, can be used to obtain additional reliable geological information about gabbro-anarthosite massifs.

Structural and tectonic features of the Transcarpathian trough according to gravity and magnetic data

Based on the analysis and interpretation of gravity and magnetic field anomalies, we studiedthe peculiarities of fault tectonics, structural-tectonic structure (including salt dome tectonics) of the Transcarpathian trough. We identified signs of the manifestation of deep faults and other large structural-tectonic elements in anomalies of gravity and magnetic fields. We then traced these structural-tectonic units by comparing the morphology, intensity, dimensions, and directions of the typical anomalous zones in the gravitational and magnetic fields with the tectonic structure of the region.
 We used digital maps of gravitational and magnetic fields; averaging transforms and relief-shadow images, we mapped local gravimagnetic anomalies. Analysis of the spatial structure of the original gravimagnetic fields and their transforms and structural-tectonic maps yielded a reflection of large tectonic elements of fault tectonics, anticlinal and salt dome structures in the gravimagnetic fields. Based on gravimagnetic data, the tectonic structure of the Transcarpathian trough was clarified, and the boundaries of tectonic zones and microplates were traced. The zone of the Transcarpathian deep fault is identified as a tectonic zone traced by a band of intense local positive anomalies of the gravity field along the Flysch Carpathians to the border of the Marmarosh massif. It is limited by high gradients from the southwest and northeast and is a reflection of the Pieniny and Marmarosh rock zones. The zone of the Transcarpathian deep fault is considered a suture zone of the Inner and Flysch Carpathians. In the structure of the anomalous gravity field of the Transcarpathian trough, a number of local anomalies associated with salt stocks, as well as individual anomalies, expected to be connected to salt-bearing deposits, werefound.
 We confirmed the effectiveness of gravimagnetic methods in the geological conditions of the Transcarpathian trough to detect anticlinal structures, basement protrusions, which create favorable conditions for oil and gas traps in sedimentary strata. Interpreting anomalous gravimagnetic fields in combination with geological and tectonic materials is an important condition for the integral process of studying the geological and tectonic structure of the Earth’s crust in the Transcarpathian region.

Anomalous field-temperature phase diagram of superconductivity in Sn–Pb solder

Sn–Pb solders are superconducting materials whose Sn and Pb are perfectly phase-separated. Recently, anomalous magnetic-flux trapping in a Sn45–Pb55 solder has been revealed, where the magnetic fluxes are selectively trapped in the Sn regions due to the supercurrents in the surrounding Pb regions. Here, we report on the observation of the anomalous critical field (Hc)-temperature (T) phase diagram of superconductivity in the Sn45–Pb55 solder. Although the Hc(T) for the Pb regions decreases with increasing field as in normal type-I superconductors and is consistent with the conventional trend with Hc(0) ∼ 800 Oe, the Hc(T) for the Sn regions exhibits anomalous behaviors. The most noticeable trend was observed in the field-cooled (under 1500 Oe) solder. The Hc-T phase diagram for the Sn regions largely varies when the applied external field is reversed, and Tc increases with increasing field amplitude when H < 0 Oe is applied. On the basis of the flux trapping and the observed anomalous Hc-T phase diagrams, we propose that the field-robust superconductivity in the Sn regions is related to the ferromagnetically aligned magnetic fluxes (or formation of vortices) in the Sn regions of the Sn45–Pb55 solder.

The Structural Zoning of the African–Antarctic Sector of the Southern Ocean Based on the Analysis of Anomalous Gravity and Magnetic Fields

The Structural Zoning of the African–Antarctic Sector of the Southern Ocean Based on the Analysis of Anomalous Gravity and Magnetic Fields

Lithospheric mantle heterogeneity beneath the Siberian craton: Evidence from garnet xenocryst database with implications for kimberlite compositions

This contribution reports some 16,000 major and minor element analyses of garnet xenocrysts derived from 18 (out of the 21 known) kimberlite fields of the Yakutian Kimberlite Province (YaKP) on the Siberian craton in Russia. Using TiO2–in–garnet as an indicator of heterogeneity within the subcontinental lithospheric mantle (SCLM), as well as garnet mg# (mg#=Mg2+/(Mg2++Fe2+)*100), we distinguish three subpopulations of garnet: 1) high content of TiO2 (0.26–0.50 wt%) and high mg# (80.6–82.6) garnet xenocrysts are common in the southern diamondiferous kimberlite fields; 2) garnet xenocrysts with low content of TiO2 (0.06–0.26 wt%) and relatively high values of mg# (78.8–81.7), which prevail in the northern ‘barren’ kimberlite fields; and 3) three anomalous northern kimberlite fields (Chomurdakh, Ogoner-Yuryakh, Toluopka) characterized by the predominance of garnet xenocrysts with high TiO2 content (0.53–0.78 wt%) at relatively low mg# (76.9–78.3).It is reasonable to assume that relatively thin cratonic mantle lithosphere beneath the three anomalous kimberlite fields underwent intense metasomatic overprinting by melts and fluids injected from the underlying asthenosphere, which changed the compositions of peridotitic garnets significantly. An interpretation of the data presented in this study is that the generally high TiO2 contents of kimberlites in the northern YaKP (>1.5 wt% TiO2) are a primary magmatic feature of asthenospheric origin because the lithospheric mantle traversed by these kimberlite magmas is TiO2 depleted. We propose a model in which the relatively thin SCLM of the northern Siberian craton provided less opportunity for high-TiO2 asthenospheric kimberlite melts to interact and change compositions on their way to the Earth’s surface. The high-TiO2 kimberlites of the northern YaKP may thus represent a good approximation of the primary compositions of natural kimberlite melts.

The Bottom Relief and the Anomalous Magnetic Field of the Ninetyeast Ridge in Near 5° N

The geophysical survey in cruise# 42 of R/V Akademik Boris Petrov (2017) at the polygon near Site 758 ODP clarified significantly knowledge about the bottom topography of the northern segment of the Ninetyeast Ridge. It is crossed by E–W transversal linear troughs, apparently being young tectonic fractures. The morphology of the narrow elevated block in the central part of the deep depression between neighboring large volcanic edifices is characterized in detail. Along with linear tectonic structures, the main features of this block are two volcanic seamounts. The detail magnetic survey at the polygon identified for the first time the nature of the sources of magnetic anomalies on the Ninetyeast Ridge. Intense local magnetic anomalies are observed here, both confined to local structures of the bottom and basement relief, and clearly unrelated to them. These anomalies are of a complex interfering nature caused by the superposition of fields from sources separated by magnetization, spatial position and age. According to the results of paleomagnetic analysis of the anomalies, the age of the structures here is very wide: the youngest features were formed about 20 million years ago, the oldest ones–over 80 million years ago.