The He isotopic composition and the He and Ne ratio of fluid inclusions in magnetite and pyrite from carbonatite breccias of the Sallanlatva alkali-ultramafic complex of the Kola alkaline province (Northwest Russia) are studied using the step-crushing method. The results indicate the highly likely involvement of fluids from several sources trapped in various proportions during the formation of the Sallanlatva explosive carbonatite breccias. The R/Ra ratio, where R is the measured 3He/4He ratio and Ra of 1.382 × 10–6 is the same ratio of atmospheric air, reaches 2.3, which is a reliable indicator of the presence of mantle gases. A low (1–44) 4He/20Ne ratio allows us to suggest the involvement of atmospheric gases dissolved in paleometeoric waters. A combination of these two facts favors a hypothesis of the phreatomagmatic nature of the studied breccias, i.e., their formation at the expense of interaction between the intruding hot orthomagmatic fluids and meteoric waters with dissolved atmospheric gases.

A channel for measuring the magnetic flux density based on four integrated Hall-effect magnetic sensors (IHMSs) is described. Built-in thermal compensation and dynamic offset cancellation circuits of IHMSs do not eliminate the sensor’s magnetic sensitivity drift due to the thermomechanical packaging stresses that causes an output-voltage offset. The placement of the sensors in a thermostatically controlled cell, as well as the design and circuit solutions related to the spatial orientation of the sensors relative to the magnetic induction vector and to the IHMS output voltage processing algorithm, made it possible to minimize the instability and increase the signal-to-noise ratio of the channel’s ADC input voltage. The design and operation of the hardware–software-based PI controller that regulates the thermostatted cell temperature are considered. The developed channel is used to measure the magnetic-field flux density of the magnetic analyzer of the mass-spectrometric system for isotopic analysis of noble gases and provides the following specifications: the measurement range is ±512 mT; the bandwidth is 0–4 Hz; the noise-free code resolution of the channel is 16.3 bits; the peak-to-peak value of the equivalent input magnetic noise in the bandwidth is 0.012 mT; and the equivalent input long-term drift of measurements is no more than 0.08 mT within 48 h.

Database containing the results of measurements of geomagnetically induced currents (GIC) for the period of 2011 to 2022 in transformer neutrals at three 330 kV substations of the main power transmission lines “Northern Transit” passing through the territory of the Republic of Karelia, Murmansk and Leningrad regions has been created and is publicly available. The GIC value depends on the geoelectric field magnitude in the Earth surface, on the relative position of the substations to which the power transmission lines are connected, and on the resistance of electrical network elements. Important factors are the electrical network branching, which determines paths of induced current spreading, and the network topology at the time of monitoring data acquisition. We describe the structure and principles of functioning of the Russian unique regional monitoring system of geomagnetically induced currents in the electrical network. We demonstrate the features of the data contained in the GIC database, which must be taken into account when processing and analyzing the data. Examples of using the GIC database for energy and geophysical studies are given. The work performed on the organization of continuous monitoring of GIC at substations of the main power transmission line in the Arctic zone has no analogues in the Russian Federation and provides extensive original material that allows us to study geomagnetic disturbances and their impact on electrical networks. The database is available at [http://gic.en51.ru]

In the FENICS experiments, performed in 2007, 2009, 2014, and 2019 under the guidance of A.A. Zhamaletdinov, unique deep electromagnetic sounding data were obtained using grounded sections of industrial overhead power lines (OHPL) at distances from 180 to 840 km from the center of the supply line to the measuring installation. At the 2014 and 2019 stages, the components of the electromagnetic field and current strength in the source were recorded with VMTU-10 (VEGA LLC, St. Petersburg) measuring equipment, which allowed synchronous processing of measurement data with GPS referencing. Unlike the previous stages, in 2019, L-403 (Murmansk–Nikel) was used as a source with a sublatitudinal direction, which differs in a number of parameters from L-401, previously used for these purposes. The paper describes the main features of the generation of ELF–ULF radiation for geophysical research using industrial power lines.

The deep electromagnetic (EM) sounding of the lithosphere carried out in the frame of the FENICS-2019 experiment from 12 to 21 September 2019 in terms of experimental layout was a frequency domain sounding with the source of two grounded industrial power lines operating in the frequency range of 192.2–0.382 Hz. The measurements were mostly carried out by the research team from Geological Institute of the KSC RAS (GI KSC) within 841 km from the source. The additional measurements by stations of the Polar Geophysical Institute, Luleå University, Nizhny Novgorod Radiophysical Research Institute (NIRFI) and the Institute of Geosphere Dynamics of the Russian Academy of Sciences (IDG RAS) were carried out at distances of up to 1470 km. The results obtained in GI KSC RAS were processed and consolidated into a database of apparent resistivity and impedance phase curves, calculated for the absolute values of the total electric and magnetic fields. The principal novelty of the FENICS-2019 experiment, distinguishing it from the AMT-MT sounding, was the quantitative account for static shift at each point. The method of correction for static shift is based on measurements of the apparent resistivity from the total horizontal magnetic field of the controlled source. Magnetometer sensors are not galvanically coupled to the Earth and therefore not affected by static shift. The method for assessing the static shift was applied within the far zone; it accounts for the influence of the ionosphere and displacement currents. Geoelectric sections were constructed for four observation profiles. This work was carried out in the frame of the state assignment of the Ministry of Education and Science of the Russian Federation for GI KSC RAS (topic No. 0226-2019-0052, FMEZ-2022-0025) and supported by the Russian Foundation for Basic Research (grant No 18-05-00528).

Recently experiments on He extraction from an amphibole by the incremental heating unexpectedly revealed that the He release pattern depends on the heating rate. During slow heating (~4 K·min−1) of the amphibole grains, one smooth peak of the He flux from the mineral was observed; in contrast, during fast heating (~40 K·min−1) an additional sharp peak appeared at a temperature about 750 °C. In order to explain these observations, we developed a model of He diffusion from the amphibole, which allowed the calculated He fluxes from the mineral to be reconciled with those observed. From the modelling we derived: (i) the helium diffusion domain size distribution, and evolution of the distribution in the course of incremental heating; (ii) occurrence of the tensile stresses, operating under enhanced temperatures above 700 °C. The stresses are different in sites with the different local thermal expansion of the crystalline lattice and they increase the He diffusion flux. The model can be applied to other minerals (materials).

Abstract —In this paper, we review the results of the deep electromagnetic soundings carried out on the Archaean blocks of the Kola Peninsula over the past 40–50 years, describe the main results of the Murman-2018 experiment, and present a critical analysis of the previous studies considering the new data. The first part of the paper addresses the results of the studies with the extremely low frequency (ELF) transmitter “Zevs” and a 40 MW MHD source “Khibiny,” the frequency soundings with a 29 kW ERS-67 car generator, and the DC resistivity soundings with vertical electrical sounding (VES) and magnetotelluric (MT) sounding setups. The review focuses on the controversial issues of the previous results for their subsequent critical analysis based on the data from the Murman-2018 experiment. The second part of the paper describes the technique, procedure, and results of the Murman-2018 experiment. The experiment included distance DC resistivity soundings (DS), controlled-source frequency soundings (Control Source AudioMagnetoTellurics, CSAMT), and audio magnetotelluric soundings (AMT) using natural variations of the Earth’s electromagnetic field. The DS and CSAMT soundings were carried out with axial and equatorial setup configurations using two mutually orthogonal current lines AB1 and AB2 with the lengths of 1.9 and 1.6 km, respectively. The key novelty of the DS measurements was the use of a linear step in changing the distance OO' between the source and receiver (2.5 and 5 km) in the range of spacings from 2.5 to 56 km. The linear step pf change of the OO' distance was used for detecting and correcting the effects of lateral and static distortions in the observation results. The DS measurements were performed along three rays directed towards West, North, and East relative to the current lines AB1 and AB2. The CSAMT measurements were performed at a distance up to 105 km from the source in combination with AMTS. Based on the results of the Murman-2018 experiment, a three-layer model of crustal structure with resistivity increasing in a gradient–stepwise manner down to a depth of 20–30 km was constructed. The resistivity in the upper layer gradually (in a gradient-wise manner) increases with depth from 10 3 Ω m on the ground to 10 4 Ω m at a depth of 1–2 km. The middle layer has a constant resistivity on the order of (1–2) × 10 4 Ω m in the depth interval from 1–2 to 10 km and is identified as a “compaction” zone. It is detected at spacings from 2–3 to 30–40 km. In this spacing interval, apparent resistivity on the ground sharply varies ​​from 5 × 10 3 to 5 × 10 4 Ω m against the average background 2 × 10 4 Ω m. The sharp swings are interpreted as the profiling effect and attributed to the influence of the fractured zones and faults intersected by the sounding path. According to the geological estimates, the faults are steeply dipping near the surface and gently dipping at depth. Their overall influence “stabilizes” “flattens” the resistivity of the middle layer at a level of 2 × 10 4 Ω m and leads to the formation of effect of intermediate conductive layer having a dilatancy-diffusion origin (DD-layer) in the depth interval from 3–5 to 7–10 km (at the base of the second layer) with a longitudinal conductivity on the order of 1 S m and resistivity within 5 × 10 3 to 10 4 Ω m. The third (bottom) layer manifests itself by a sharp stepwise increase in electrical resistivity up to 10 5 –10 6 Ω m and higher. The top surface of this layer is located at a depth of 10–15 km and is conditionally interpreted as an “impenetrability boundary” for direct current. This boundary marks the Brittle–Ductile Transition Zone (BDT) of the rocks. A critical analysis of the previous results in the light of the new data obtained in the Murman-2018 experiment is conducted in the Discussion section.

A digitally controlled high-precision low-noise high-voltage source is described. A push–pull parallel resonant voltage converter with a constant switching frequency of 110 kHz is used in the source. The high-voltage source is adjusted by changing the output voltage of a linear voltage regulator that feeds the resonant converter. An algorithm for controlling the converter switches that makes it possible to implement a mode of supplying the parallel circuit of the converter from the voltage source is proposed. An automatic frequency control system ensures the temperature stability of the converter operating mode. An active ripple filter was designed. Its main feature is the application of a compensating voltage between the common bus of the source and the low-potential output of the voltage multiplier. This solution made it possible to construct the filter based on one low-voltage op-amp, which is simultaneously used as an error signal amplifier of the source control loop. As a result of applying the active filter, the output noise and ripple peak-to-peak amplitude at frequencies higher than 10 Hz does not exceed 3.3 mV. The peak-to-peak noise in the frequency range of 0.1–10 Hz is below 3.5 mV and is determined by the 1/f noise level of the used voltage reference. The developed high voltage source is used in the ion source power supply of the mass-spectrometry system for isotope analysis of noble gases and has the following specifications: the output-voltage control range is 0–5500 V with a step of 84 mV; the maximum load current is 1 mA; and the overall output voltage instability is no more than 50 ppm/h in the operating temperature range of 20–50°C.

5 Лаборатория свойств стекла, Санкт-

A new portable system for measuring the grounding resistance of transmission towers equipped with overhead ground wires (OHGWs) was developed. To predict the lightning performance of power lines, electric power companies until now measure the low-frequency grounding resistance. A new technique of processing the transient impedance time-dependency obtained by injects of a fast-rising pulse current into a tower base was developed. The technique allows the estimation of element values for a simple lumped RLC equivalent tower grounding circuit, suitable for use across a wide range of soil resistivity values. The tower grounding resistance value finally calculated from the obtained resistance value of the equivalent circuit, by accounting for the parallel-connected surge impedances of OHGWs. For the measuring system, a pulse generator based on inductive energy storage was designed. Since an inductive generator's current pulse shape is not distorted due to a reflection from the remote end of the current lead, therefore, the rather short potential and current leads of 50-meter long and short ground rods could be used. The pulse has 100 ns rising time and constant amplitude within the time of measurement interval, which is limited only by the arrival time of a current wave reflected from the nearest OHGW-connected tower. In the implemented prototype, the main instrumentation requirements for field measurements, such as low weight and dimensions, autonomous power, dust and moisture protection, usability, and easy maintenance, were taken into account. The general hardware structure, operational principles, and main technical specifications of the portable measuring system prototype are discussed in the paper along with the field test results.

Results of study of supposed boundary of impenetrability in the crystalline earth crust are discussed in the article. The Murman-2018 experiment on distance DC sounding in combination with frequency and audio magnetotelluric sounding was undertaken to solve the problem. Methods of field work and data processing are presented in the first part of the work. The second part of the work is devoted to the interpretation method description and to presentation of results obtained. Impenetrability boundary is detected in the shape of the sharp resistivity increase from 104 to 106 Ω · m at a depth of 10–15 km. That boundary is accepted as transition zone between the brittle and ductile states of the earth crust substance (Brittle-Ductile Transition zone, BDT). To obtain the more reliable information on parameters of the impenetrability boundary it is necessary to conduct additional DC studies using remote sensing at distances up to 1000 km between transmitter and receiver.

The paper presents a low-cost system for monitoring the condition of metal-oxide surge arresters (MOSAs) in service. The developed system integrates two methods currently used for evaluating the condition of surge arresters: registration of transient overvoltages experienced by a MOSA and analysis of leakage current. A surge counter with a built-in primary leakage current sensor (SCLCS) is mounted on a MOSA to register the date, time, and value of charges carried by the discharge currents through a MOSA. The SCLCS powered by a long-life battery stores the recorded data in non-volatile memory. A measurement module connected successively to each SCLCS reads the registered data and performs a leakage current analysis, which involves the determination of the resistive component and the 3rd, 5th, 7th harmonics of the total leakage current. The voltage reference signal received from the secondary side of the potential transformer is wirelessly transferred by a transmitting unit. Six-year experimental testing of the developed prototypes installed at several distribution substations produced satisfactory results. The conducted tests confirmed the efficiency of leakage current analysis not only for detecting deterioration in the MOSA condition but also for differentiating its cause. Data obtained by an SCLCS provides useful information on lightning and switching transient overvoltages arising in a particular network segment, the efficiency of the arrester operation, and the amount of energy absorbed by the MOSA. The paper describes the hardware implementation, operational principles, and main technical specifications of the proposed system. The results of the pilot testing of the system are presented.

A high-dynamic-range counting−analog detector system based on a secondary electron multiplier (SEM) is described. The current-to-voltage converter, which is common to both channels, includes a high-speed transimpedance amplifier (TIA) and an automatic bias-correction circuit. This circuit also rejects 1/f noise of the TIA in the 0−2.3 Hz passband of the digital lowpass filter of a 24-bit analog-to-digital converter (ADC) in the electrometric channel. As a result, the noise-free code resolution of the entire channel, which is 18.5 bits, is determined only by the ADC noise. A number of circuit solutions are proposed to minimize the number of circuit components, which have made it possible to place the detector system board in the measuring head of the SEM and thereby reduce the stray capacitances that limit the response speed of the TIA. The maximum counting rate of the pulse-counting channel is 7 ×107 cps and is determined by the time resolution of the SEM. The problems of optimizing the supply voltages of the circuit and the gain of the SEM in the counting−analog mode are considered. The developed system is one of the units of the mass-spectrometry system for the isotope study of noble gases. The SEM-input-referred measurement ranges of the system are as follows: from 1 × 10–16 to 1.2 × 10−11 A at a resolution of 3 × 10−17 A or better for the electrometric channel; from 5 × 10−2 to 5 × 107 ions/s for the pulse-counting channel without counting losses and with the allowance for the SEM dark current; and from 1 × 10–20 to 1.2 × 10−11 A for the entire system. Due to the wide overlap of the measurement ranges, it is possible to perform mutual verification of data obtained in different modes.

Studies of 40Ar and 4He mobility in minerals (performed for isotope geochronometry problems) generally assumed that the migration parameters, obtained for the atoms preserved in a mineral, described the mobility of all atoms that were produced in the mineral, including those that were lost in the past. To test this assumption, an analysis of the U-Th-Li-4He-3He isotope system in amphiboles, separated from alkaline granites of the Ponoi massif, Kola Peninsula, was performed. The retention of He isotopes was determined, i.e., the ratio of the amount of radiogenic He remaining in a mineral to its amount, which should have been accumulated since the formation (metamorphism) of the mineral. It turned out that 36% of 3He and only 14% of 4He were preserved in the mineral. The results of experiments on 3He and 4He migration from amphibole grains during their step wise heating in vacuum were successfully approximated by a diffusion model. However, the parameters, obtained during the simulations, did not allow reproducing the above retentions of He isotopes. The mechanisms of 3He and 4He migration in the past, which have led to such different retentions, differ from the diffusion mechanism, which adequately describes migration of the atoms remaining in the mineral.

The article describes the experiment “Murman-2018” on remote electromagnetic sounding in combination with frequency and audio magnetotelluric soundings. The current from 29 kW power car-generator was fed into the ground using two mutually orthogonal grounded electric dipoles 1.6 and 1.9 km long. The measurements were carried out along three traces with maximum distances from the source up to 105 km in the mode of frequency sounding (in the range of 4-1000 Hz) and up to 56 km in the mode of remote sensing at direct current. The data processing was performed in the spectral mode and in the accumulation mode. The results of the experiment made it possible to quantify for the first time in the scientific literature the position of the boundary of a sharp increase in rock resistance at a depth of 10-15 km. The nature of the established boundary (the boundary of the “impenetrability” for direct current) is associated with the transition of the properties of the rocks of the Earth's crust from the fragile state in the upper crust to a plastic state at depths of 10-15 km and more. In foreign literature, this boundary is defined as the BDT-zone (brittle-ductile transition zone).