Anomalous Magnetic Field Research Articles

Spatial Analysis of Airborne Geophysical Data Applied to Geological Mapping and Mineral Prospecting in the Serra Leste Region, Carajás Mineral Province, Brazil

The Serra Leste region, located in the northeast portion of Carajas Mineral Province (PA), hosts important chrome-PGE, Au–Pd–Pt, Cu–Mo–Au, iron, and manganese deposits and occurrences related to different geological settings. We present a regional prospective model with focus on PGE mineralizations based on airborne geophysics (magnetometry, gamma-ray spectrometry and time domain electromagnetometry) and geological data. Geological and geophysics data analysis indicate a plausible correspondence between areas with meta-mafic–ultramafic rocks and low values in gamma spectrometry, mainly for the thorium channel. The meta-ultramafic units of the complexes, the main host rock of the PGE mineralization, are well defined by analytic signal from the anomalous magnetic field and by the apparent conductance anomalies derived from the GEOTEM system. The combination of the derivative products with updated geological data of the Serra Leste region and PGE-Luanga deposit enable to establish a regional prospective model for PGE and the identification of new targets within the studied area.

Age of the western Black Sea basin according to an analysis of the anomalous magnetic field and geological data

Until recently, the ideas about the age of the Black Sea deep-water basin have been based on land geological observations in the coastal areas at the interaction periphery, underwater observations from manned submersibles, and on the data of seismic reflection and refraction studies and drilling. Formerly, the scarcity of the information led to a wide scattering of the age determinations: from the Jurassic to the Eocene. Recently, with the appearance of reliable geological and geophysical data, the range of the age estimates has been considerably reduced during the last few years, although there is no commonly accepted opinion on this issue. Therefore, the first attempt to determine the age of the Western Black Sea basin using an analysis of the anomalous magnetic field is of certain interest. The following results were obtained: the basin probably opened between 71.338 and 71.587 My B.P. (subchron C32n.1r). During the interval 68.737–71.071 My B.P. (subchron C31r), extinction of the spreading axes took place. Thus, the total duration of the Campanian-Maestrichtian phase of the opening was about 3 My (interval from 71.587 to 68.737 My B.P.). This result does not agree with the geological and geophysical data available to date. To solve this problem, collection of new geological data and further studies of the structure of the anomalous magnetic field are required.

Typification of the Earth’s crust of Central Arctic Uplifts in the Arctic Ocean

The modern views on the structure of the oceanic and continental crust are discussed. The presented geological-geophysical information on the deep structure of the Earth’s crust of the Lomonosov Ridge, Mendeleev Rise, and Alpha Ridge, which make up the province of the Central Arctic Uplifts in the Arctic Ocean, is based on CMP, seismic-reflection, and seismic-refraction data obtained by Russian and Western researchers along geotraverses across the Amerasia Basin. It is established that the crust thickness beneath the Central Arctic Uplifts ranges from 22 to 40 km. Comparison of the obtained velocity sections with standard crust sections of different morphostructures in the World Ocean that are underlain by the typical oceanic crust demonstrates their difference with respect to the crustal structure and to the thickness of the entire crust and its individual layers. Within the continental crust, the supercritical waves reflected from the upper mantle surface play the dominant role. Their amplitude exceeds that of head and refracted waves by one to two orders of magnitude. In contrast, the refracted and, probably, interferential head waves are dominant within the oceanic crust. The Moho discontinuity is the only first-order boundary. In the consolidated oceanic crust, such boundaries are not known. The similarity in the velocity characteristics of the crust of the Alpha Ridge and Mendeleev Rise, on the one hand, and the continental crust beneath the Lomonosov Ridge, on the other, gives grounds to state that the crust of the Mendeleev Rise and Alpha Ridge belongs to the continental type. The interference mosaic pattern of the anomalous magnetic field of the Central Arctic Uplifts is an additional argument in favor of this statement. Such patterns are typical of the continental crust with intense intraplate volcanism. Interpretation of seismic crustal sections of the Central Arctic Uplifts and their comparison with allowance for characteristic features of the continental and oceanic crust indicate that the Earth’s crust of the uplifts has the continental structure.

Locating geologic contacts with magnitude transforms of magnetic data

Locating geologic contacts by mapping lateral magnetization changes provides a variety of useful geologic information. Magnetic contacts will often correspond to lithologic boundaries, while the shapes and textures of contact maps can also indicate rock type and the style of deformation present. Well-established methods for contact mapping are the horizontal gradient magnitude of the pseudogravity (PSG-hgm) and the total field (TF-hgm). More recent mappers include the analytic signal (AS), the 3-D local wavenumber (LW) and the horizontal gradient magnitude of the tilt (TI-hgm). PSG-hgm and TF-hgm generally produce coherent contact trends but the locations are dependent on the contact dip and its magnetization direction. The AS, LW and TI-hgm methods produce contact locations that are independent of dip and magnetization. Magnitude transforms of the anomalous magnetic field offer an alternative approach to contact mapping since only the field components or the field component derivatives are used, in contrast with other methods that require total field derivatives, possibly up to second order. The magnitude transforms are also dip- and magnetization-independent. Contact maps determined for the magnitude transforms are compared with those from the PSG-hgm and TF-hgm methods for a recently-flown survey over a poorly-exposed Precambrian Shield area in Manitoba, Canada. The T transform map (magnitude of the anomalous magnetic field) is similar to that from PSG-hgm. The other magnitude transforms perform less well because of sensitivity to noise and gridding artefacts, resulting in less coherent trends. None of the transforms are able to resolve the same detail that TF-hgm does. Contact maps from magnitude transforms are therefore only to be preferred over PSG-hgm and TF-hgm maps in areas of high remanent magnetization and gently dipping geology.

Analysis of the geomagnetic field of the White Sea: The Gorlo Strait

The objective of our research is the interpretation of the results of the geomagnetic survey of the geologic structure in the Gorlo Strait of the White Sea. We used the maps of the anomalous magnetic field (AMF) available and processed them with original interpretation software. As a result of this processing, we compiled a structural-tectonic chart of this region. We distinguished the boundaries of the major first-order tectonic structures such as the underwater extension of the Leshukon graben and a number of minor structures related to the Proterozoic and Paleozoic stages of the magmatic activity in the region. Modeling was performed for the most important objects, which allowed us to refine the geological structure of these objects and their genesis.

High‐resolution multifluid simulations of the plasma environment near the Martian magnetic anomalies

Three‐dimensional high‐resolution (∼40 km), multifluid simulations of the solar wind interaction at Mars during the southern hemisphere summer solstice indicate that the region around the magnetic anomalies can be complex and highly structured. The anomalous magnetic field leads to the formation of multiple cusps and a void region where the ionosphere is eroded. Most importantly, the anomalous magnetic field changes the nature of the magnetic pileup layer (MPL) when compared to over unmagnetized regions. While the altitude of the MPL is approximately the same in both the northern and southern hemispheres for this orientation, plasma in the MPL near the magnetic anomalies is cooler, with less solar wind and more of ionospheric origin. The solar wind density is reduced by a factor of 3 in the southern MPL, in comparison to the northern MPL, while the ionospheric density is 10–600 times more dense in the southern MPL, depending on altitude, location, and species.

Magnetic loss in soft ferrites

In order to understand the anomalous magnetic field dependence of the high frequency (200kHz–1.0MHz) losses, we consider the high field conductivity of the soft ferrites. We show that the high field conductivity is highly nonlinear. Separately, we show that this nonlinear behavior is due to tunneling between adjacent ferrite grains. In this paper we show that this tunneling based nonlinear conductivity gives rise to a different eddy current loss, which can explain the anomalous magnetic field dependence of the measured high frequency loss.

High-pressure Study of a Doped-type Organic Superconductor, κ-(BEDT-TTF)4Hg2.89Br8

Physical properties of the organic charge-transfer complex that may be regarded as a doping system are presented. We measured resistivity of an ambient-pressure superconductor, κ-(BEDT-TTF)4Hg2.89Br8, as functions of temperature, magnetic field, and pressure. Metallic and superconducting states of this salt are possibly attributable to the doping effect, which originates from incommensurability of Hg chain because band structure calculation predicts strong electron-electron correlation enough to localize the itinerant electrons. We uncovered anomalous pressure and magnetic field dependences of superconductivity as well as non-Fermi liquid behavior in the normal-state resistivity at low pressures. In addition, we observed a pressure-induced crossover to the Fermi liquid behavior, which is seen in non-doped κ-type salts at any pressures.

Resonant susceptibility of dielectric glasses in magnetic field

The anomalous magnetic field dependence of dielectric properties of insulating glasses in the temperature interval $10mK<T<50mK$ is considered. In this temperature range, the dielectric permittivity is defined by the resonant contribution of tunneling systems. The external magnetic field regulates nuclear spins of tunneling atoms. This regulation suppresses a nuclear quadrupole interaction of these spins with lattice and, thus, affects the dielectric response of tunneling systems. It is demonstrated that in the absence of an external magnetic field the nuclear quadrupole interaction $b$ results in the correction to the permittivity $\delta\chi\sim| b| /T$ in the temperature range of interest. An application of a magnetic field results in a sharp increase of this correction approximately by a factor of two when the Zeeman splitting $m$ approaches the order of $| b| $. Further increase of the magnetic field results in a relatively smooth decrease in the correction until the Zeeman splitting approaches the temperature. This smooth dependence results from tunneling accompanied by a change of the nuclear spin projection. As the magnetic field surpasses the temperature, the correction vanishes. The results obtained in this paper are compared with experiment. A new mechanism of the low temperature nuclear spin-lattice relaxation in glasses is considered.

Possible chiral magnetism in [formula omitted

We reported here commensurate-to-incommensurate (C-IC) magnetic ordering in copper metaborate CuB 2 O 4 on the basis of concomitant chiral soliton lattice formation. We measured the magnetization processes in detail under the applied magnetic fields parallel and perpendicular to the helical axis. We found the anomalous temperature and magnetic field dependence of the magnetization strongly anisotropic with respect to the applied magnetic fields. The experimental results were quite consistent with the theoretical prediction based on the lattice chiral XY model, which describes the C-IC transition as the chiral soliton picture.

Calculation of magnitude magnetic transforms with high centricity and low dependence on the magnetization vector direction

We present a Matlab tool that calculates five magnitude magnetic transforms (MMTs) from an input measured anomalous magnetic field. The MMTs are all based on the total magnitude anomaly (TMA), and consist of the TMA itself, the modulus of the gradient of the TMA, the Laplacian of the TMA, half of the square root of the Laplacian of the square of the TMA, and the square root of the product of the TMA plus the Laplacian of the TMA. These MMTs produce anomalies that are closer to the magnetic source’s true horizontal position and are simpler to interpret than the measured anomalous magnetic field itself. While the conventional magnetic transforms of reduction-to-the-pole (RTP), the pseudogravity field, and the analytic signal (AS) also have these properties, these MMTs have several additional advantages. They require only first-order, horizontal derivatives for their calculation. They are also more stable at low magnetic latitudes than the RTP, and have a pattern that is independent of the geomagnetic-field vector direction, in contrast to the AS. The Matlab tool is designed to deal with big data sets and is compatible with common data formats, GS ASCII grid files, and XYZ data files. A calculation of the MMTs of the total magnetic anomaly of a synthetic example at a low magnetic latitude and with a field example from the Kuju volcanic area, Japan demonstrate the effectiveness of the program.

Formation of the Eurasia Basin in the Arctic Ocean as inferred from geohistorical analysis of the anomalous magnetic field

A new combined magnetic database and a magnetic-profile map are developed for the Eurasia Basin as a result of adjusting all available historical and recent Russian and American magnetic data sets. The geohistorical analysis of magnetic data includes several steps: identification of linear magnetic anomalies along each trackline, calculation of the Euler rotation pole positions for the relative motion of the North American and Eurasian plates, analysis of temporal and spatial variations in the spreading rate, and plate reconstructions. The pattern of key Cenozoic magnetic isochrons (24, 20, 18, 13, 6, 5, 2a) is constructed for the entire Eurasia Basin. In the western half of the basin, this pattern is consistent with a recently published scheme [16]. In its eastern half, magnetic isochrons are determined in detail for the first time and traced up to the Laptev Sea shelf. The main stages in the seafloor spreading are established for the Eurasia Basin. Each stage is characterized by a specific spreading rate and the degree of asymmetry of the basin opening. The revealed differences are traced along the Gakkel Ridge. Systematic patterns in wandering of the Eurasia Basin opening pole are established for particular stages. The continent-ocean transition zone corresponding to the primary rupture between plates is outlined in the region under consideration on the basis of gravimetric data. The nature of different potential fields and bottom topography on opposite sides of the Gakkel Ridge is discussed. The characteristic features of the basin-bottom formation at main stages of its evolution are specified on the basis of new and recently published data. The results obtained are in good agreement with plate geodynamics of the North Atlantic and the adjacent Arctic basins.

Reconstruction of the harmonic component of the magnetic field modulus anomalies

An algorithm is proposed for calculating a harmonic function equal to the projection of the anomalous magnetic field vector onto the normal field direction from in situ measurements of the anomalous magnetic field modulus (the scalar magnetic anomaly) ΔT, which is a nonharmonic function and is nonlinearly related to the magnetization of anomaly sources. It is shown that the inferred estimates tend to the desired harmonic function if the iterative algorithm converges. The convergence conditions and stability of the process are studied numerically in a wide range of amplitudes of the anomalous field. The results of the modeling simulation demonstrate the efficiency of the proposed algorithm in solving magnetic field interpretation problems often encountered in practice.

Anomalous magnetic field of the Lomonosov Rise according to data of the north pole 19 drifting station

The technique for determining the normal and anomalous magnetic fields from magnetovariation observations has been applied to the measurements on the SP19 drifting station. As a result, the regional profile of three magnetic field components has been obtained to an accuracy considerably exceeding the accuracy of other methods of marine magnetic survey. These data make it possible to estimate the geometrical parameters of the Earth’s crust blocks composing the Lomonosov Rise.

Inversion of elongated magnetic anomalies using magnitude transforms

ABSTRACTThe calculable magnitudes of the anomalous magnetic field from simple 2D sources and their gradients and Laplacians appear as ratios that can be synthesized in functional forms, corresponding to the different source shapes. Field components and first‐order derivatives are involved in the inversion procedures presented. The structural index and source depth are estimated independently of each other. The applied functions allow magnetic profiles and magnetic maps to be shape‐ and depth‐converted with immediate imaging of the inversion results. The contours of these functions outline elongated loops around the 2.5D anomaly axis on magnetic maps. The width of the loops reflects the depth and structural index N of the source in the scale units of the inverted map. Model and field tests illustrate the effectiveness of this approach for fast automatic inversion of large sets of magnetic data for depth, shape, length and location of simple sources.

Evolution of the southern part of the Canada Basin (Arctic Ocean) based on magnetometric data

Using a new Russian‐American digital grid of anomalous magnetic field of the Arctic Ocean [1], oceanic magnetic anomalies were identified for the whole southern part of the Canada Basin (hereafter, southern CB), extending from the eastern scarp of the Northwind Ridge to the adjacent Banks Island‐Mackenzie Delta continental margin. The geohistorical analysis of magnetic anomalies carried out based on the original procedure [2] revealed regional features of the basin evolution. Contradictory ideas about this evolution were so far based on the geology of continental framing. The presence of spreading-related, fan-shaped magnetic anomalies in the southern CB has been known since the 1970s [3]. However, the strike of anomalies adjoining them has not been established, and the satellite gravitation minimum showed that the extinct spreading center (SC) occurs 75 km eastward of the site assumed by American geophysicists [4]. The available digital grid of the anomalous mag

Anomalous Magnetic Field Effects Interpreted by the Relaxation Mechanism under Ultrahigh Fields of up to 28 T

Abstract Magnetic field effects on the triplet sensitization reaction of p-aminophenyl disulfide were studied in a sodium dodecylsulfate micellar solution by a nanosecond laser flash photolysis technique under ultrahigh magnetic fields of up to 28 T. The yield of the escaped p-aminophenyl thiyl radical decreased by 6 ± 2% at 28 T compared with that at 0 T.

Dynamics of the Saturnian inner magnetosphere: First inferences from the Cassini magnetometers about small‐scale plasma transport in the magnetosphere

The Cassini magnetometers reveal a very dynamic plasmadisc within the inner Saturnian magnetosphere during the first three orbits of the Cassini orbital tour. This corotation‐dominated region is known to contain various neutral and plasma populations and Voyager spacecraft observations suggest important radial transport processes redistribute the locally created plasma out to the remote magnetospheric regions, by a mechanism yet to be identified. In this work we report on anomalous magnetic field signatures in the inner regions of the magnetosphere (inside of 8 Saturn radii) that may participate in the radial transport and that seem to be consistent with signatures of interchanging flux tubes. These unusual events are characterized by sharp boundaries and abrupt changes of the magnetic pressure, consisting of depressions or enhancements of the field magnitude. They present some similarities with previously identified signatures of interchanging flux tubes in the Io torus, allowing the interesting possibility of carrying out a comparative study of these two environments.

The Total Field Magnetometric Resistivity(TFMMR) Method Part II: 2D resistivity inversion of data from the Flying Doctor Deposit, Broken Hill, Australia

Total field magnetometric resistivity (TFMMR) is a highresolution electrical technique that yields information on subsurface resistivity. In a companion paper (Fathianpour et al., 2005, Part I) the basis of a 2.5D TFMMR finite-element modelling approach was developed for a point current source in an otherwise 2D resistivity structure. In this paper (Part II), we use the 2.5D forward modelling algorithm as the basis of a numerical inversion for 2D resistivity structure using a Marquardt-Levenberg algorithm. Application of a quasi-Newton updating formula for approximating the Fréchet derivatives in the course of inversion results in a fast and reliable routine. To overcome the problems of the effect of the geomagnetic field direction and dependency of TFMMR data on all three vector-components, field data are initially reduced to the pole. By doing this, we require only Fréchet derivatives for the vertical Bz anomalous magnetic field, and in the case of the 2D structures, Bz is the most sensitive component to vertical boundaries separating lateral changes in resistivity.TFMMR data collected across the Flying Doctor Deposit, near Broken Hill in New South Wales, Australia are inverted for 2D resistivity structure. The inverse models show the presence of a conductive zone in the central part of the surveying area corresponding to the known mineralisation and the Globe Vauxhall Shear Zone. Depth resolution is limited, but we demonstrate that the method can resolve lateral boundaries.

Charge dynamics and Kondo effect in single-electron traps in field-effect transistors

We study magneto-electric properties of single electron traps in metal-oxide-semiconductor field effect transistors. Using a microscopic description of the system based on the single-site Anderson-Holstein model, we derive an effective low energy action for the system. The behavior of the system is characterized by simultaneous polaron tunneling (corresponding to the charging and discharging of the trap) and Kondo screening of the trap spin in the singly occupied state. Hence, the obtained state of the system is a hybrid between the Kondo regime, typically associated with single electron occupancy, and the mixed valence regime, associated with large charge fluctuations. In the presence of a strong magnetic field, we demonstrate that the system is equivalent to a two level-level system coupled to an Ohmic bath, with a bias controlled by the applied magnetic field. Due to the Kondo screening, the effect of the magnetic field is significantly suppressed in the singly occupied state. We claim that this suppression can be responsible for the experimentally observed anomalous magnetic field dependence of the average trap occupancy in ${\rm Si-Si0_2}$ field effect transistors.