Sources Of Magnetic Anomalies Research Articles

On the Crustal Sources of Magnetic Anomalies in the Middle Urals

The 800×500 sq km area of the the Middle Urals, Russia, lying between 56 to 60° northern latitude and 54 to 66° eastern longitude, was studied in terms of the deep crustal structure. The study was based on three-dimensional modeling of the sources of magnetic anomalies in three layers of the Earth’s crust. The studied area covers the folded region of the Urals and adjacent structures of the East European Platform and the West Siberian Plate. The sources modeled in the near-surface layer down to a depth of 5 km make it possible to clarify the position of magnetized massifs, mainly consisting of mafic-ultrabasic rocks, and to trace their connection with mafic-ultrabasic belts in the granite layer and root blocks in the lower basaltic layer of the Earth’s crust. When the sources in the upper crustal layer are compared with those in the lower crustal layer, it is apparent that many belts on the platform have deep-seated roots and are located above the basalt layer protrusions, while most of the massifs in the Urals do not have deep-seated roots. The springs located under the western slope of the Urals allow reliably determining the depth to the basement of the ancient platform and the location of the eastern border of the East European Platform in the lower layer of the Earth’s crust. There were found extended zones of subsidence of the roof of the lower magnetized layer, which probably mark the boundaries of various terrains forming the paleo-island arc sector of the Ural fold system. The most extensive subsidence of the roof of the lower layer occurs to the west of the Tyumen-Chudinovsky fault and is perhaps the eastern deep-seated dividing line between the Ural fold system and the West Siberian Plate.

Глубинное строение Среднего Урала по гравитационным и магнитным данным

For the Middle Urals and adjacent territories of the East European and West Siberian platforms within geographic coordinates from 56º to 60º northern latitude and from 54º to 66º east longitude, the structural features of the anomalous magnetic and gravitational fields were studied and maps of separated anomalies were constructed for three layers of the earth's crust. Using original parallel algorithms for solving forward and inverse problems of gravimetry and magnetometry, a density model of the lithosphere and sources of magnetic anomalies in the earth's crust were constructed. The results of modeling the sources of magnetic anomalies in the Earth's crust are compared with the density model in order to study the differences in the deep structure of the western paleocontinental and eastern paleo-island arc sectors of the Ural fold system, as well as the zones of junction of the orogen with the East European and West Siberian platforms.

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.

Geomagnetic Studies in the Norther Atlanic

The paper deals with the description of new geomagnetic data collected in the North Atlantic during voyages of research vessels of the Russian Academy of Sciences performed in 2020–2022. Modern technologies of geomagnetic measurements in the ocean and methods of their processing are considered. The obtained geomagnetic data indicate the heterogeneous nature of the sources of magnetic anomalies in the Charlie-Gibbs fault zone and adjacent areas of the Mid-Atlantic Ridge and allow solving a wide range of geological and tectonic problems. Priority directions for further research aimed at adjusting spreading parameters and constructing models of the magnetic layer typical for transform faults and amagmatic segments of the Mid-Atlantic Ridge are formulated.

3D Geophysical and Geological Modeling of the South Orkney Microcontinent (Antarctica): Tectonic Implications for the Scotia Arc Development

AbstractThe opening of the Scotia Arc resulted in the final breakup of the land bridge between South America and the Antarctic Peninsula. The South Orkney Microcontinent (SOM) constituted part of this former connection and it is now the largest continental block in the Southern Scotia Arc. We present the first 3D model of the SOM that, given its strategic position and characteristics, allows us to advance the knowledge of the tectonic processes involved in the development of the Scotia Arc. Due to the scarcity of reliable geological data, the initial approximation of the deep structure of the SOM was supported by the calculation of three main geological boundaries from geophysical data: the acoustic basement, the boundary of the magnetic anomaly source and the Moho depth. The 3D model was built, refined and validated by forward modeling and joint inversion of gravity and magnetic data. We have accurately defined the geometry of the sedimentary cover, determined the geometry of the intrusive igneous body causing the Pacific Margin Anomaly (PMA) and mapped the heterogeneity of the crustal thickness. These structural features show a clear relationship to each other and are consistent with an important E‐W extension to the east of the SOM during early stages of the Scotia Arc formation, prior to the opening of the Powell Basin.

Magneto-mineralogical characteristics of mafite-ultramafites of the Middle Bug River area and Holovaniv suture zone of the Ukrainian Shield (overview)

Mafites and ultramafites manifest in the magnetic field as significant magnetic anomalies due to the high content of magnetite, titanomagnetite and iron-magnesium silicates. Studying the mineralogy and magnetic properties of Archean rocks formed deep in the lower crust and uplifted to the surface allows to understanding the sources of magnetic anomalies. Such rocks are known in the Ukrainian shield, in particular in the Middle Bug River region and in the Holovaniv suture zone (HSZ). We consider mafic-ultramafic assemblages of the rocks of this region, their mineral composition and magnetic characteristics, manifestations in the magnetic field, and the distribution of magnetic minerals. Several mafic-ultramafic associations of different ages, composed of effusive, sedimentary-effusive and intrusive formations, are recognized for the area the Pobuzkiy ore mining region. Most of them were transformed intensively by metamorphism of granulite (to eclogite) facies and by intense tectonic and diaphoretic processes. The main volcanics and volcanogenic-sedimentary rocks belong to the Tivriv stratum of the Paleoarchean Dniester-Bug and Neoarchaean Bug series. Mantle rocks were the protolith of the Tivriv stratum, which are similar in composition to oceanic basalts. The Pavliv stratum is considered as a part of the Dniester-Bug series. It is composed mainly of two-pyroxene crystal schists (sometimes amphibolized, often with significant magnetite content (up to 10 %)), magnetite-orthopyroxene crystal schists, and bodies of ferruginous quartzites. Both series contain gneiss complexes, as well as bodies of basite-hyperbasites. Mafic rocks are mainly represented by hornblende-pyroxene crystal schists and amphibolites. Ultramafite and mafit-ultramafite intrusive bodies were mapped in the central and northern parts of the HSZ where they are presented by rocks of the hyperbasite and gabbro-peridotite formations. The Holovaniv block of the HSZ is spatially coincident with the Holovaniv gravitational maximum and magnetic anomalies, which are probably caused by the rooting of mafit-ultramafits from the upper mantle along deep fault zones. Magnetic sources with increased magnetization were identified within the district of Haivoron. They are associated with pyroxene schists, gneisses, coarse-grained pyroxene schists, and ferruginous quartzites. The high values of magnetic parameters of the rocks of the Haivoron-Zavallya region are explained by the presence of eulysites and magnetite-hypersthene crystal schists. Within the area of occurence of charnockite-enderbite rocks, the magnetic field with increased intensity and a large-mosaic structure is observed. Differentiation of the magnetic properties of the rocks of the upper part of the Earth’s crust, the shape and low power of the sources indicate their possible primary magmatic formation in the form of massifs and dykes with further metamorphic transformations. Magnetite is the main magnetic mineral of mafite-ultramafites according to thermomagnetic analysis and ore microscopy. Several generations of magnetite are observed. Early generations (reliably magmatic) are present in the dark-colored minerals as point inclusions and emulsion discharges along fissures (disintegration structures of solid solutions). The increase of the amount of magnetite in all types of rocks is associated with superimposed secondary transformations. Redistribution of iron occurs in the recrystallization zones with the formation of clusters of secondary coarse-grained magnetite. According to the hypothesis, the magnetite of ferruginous quartzites has metamorphic origin, while the origin of the magnetite of iron-carbonate and iron-siliceous formations is a controversial issue. It depends on the determination of the genesis of the original substance.

Relation between Magmatic and Tectonic Processes in the Formation of the Oceanic Crust to the South of the Charlie Gibbs Fracture Zone (North Atlantic)

The article presents new data on the structure and relationship of tectonic and magmatic processes during the formation of the Mid-Atlantic Ridge between the Charlie Gibbs and Maxwell fracture zones in the North Atlantic. It is shown that this region is characterized by significant reduction in volcanism, which leads to the excavation of low crustal and upper mantle rocks to the surface. Both individual inland oceanic complexes of the most varied configurations and extended sublatitudinal ridges composed of plutonic rocks are formed. Our analysis showed that this formation setting existed for at least 14‒16 Ma. The formation of most internal oceanic complexes is associated not only with tectonic factors, but also with the serpentinization of peridotites, which leads to a decrease in density, an increase in volume, and, as a result, to the emergence of large ultrabasic massifs, including separated blocks of gabbroids, dolerites, and basalts. Numerous zones of sliding, crushing, abrasion and deformation of rocks indicate tectonic movements. The study region is characterized by numerous non-transform displacements of different amplitudes, which are formed under conditions when relative displacements of oceanic lithosphere segments are realized in wide areas undergoing shear and extension deformations. The morphology of the emerging tectonic-magmatic structures of the region is determined by tectonic factors. The exceptions are cases when the volumes of melts entering the surface in a short period of time are significantly higher than the average for a certain segment of the rift valley. The analysis performed shows the presence within the region of sources of magnetic anomalies that are heterogeneous in nature, both of volcanic origin and associated with manifestations of superimposed tectonic activity.

Results of Modeling Sources of Magnetic Anomalies in the Earth’s Crust in the Middle Urals

Results of Modeling Sources of Magnetic Anomalies in the Earth’s Crust in the Middle Urals

The nature of magnetic anomalies in the southern part of the Barents Sea shelf according to the results of an integrated analysis

Research subject. The anomalous magnetic field of the southern part of the Barents Sea Shelf.Materials and methods. The research was based on a digital matrix (grid) of the anomalous magnetic field (AMP) compiled from the materials of magnetic surveys performed in 2002–2007 by a number of research organizations and research and production companies. A model describing the structure and formation of the magneto-active layer of the southern part of the Barentsevomorsk region was developed. An analysis of the radially averaged field spectrum made it possible to establish the confinement of the upper edges of the field sources to several structural horizons. Band filtering in the frequency domain in accordance with the allocated depth ranges allowed anomalies to be distinguished from other sources. To determine the nature of sources of magnetic anomalies at different levels of the earth’s crust, an integrated analysis of gravimagnetic fields, seismic profiling data and ground studies was conducted.Results. At least two levels of magnetic anomaly sources were found: the distribution of effective magnetization for the low-frequency component of AMP, reflecting the depth structure of the region, and the high-frequency component of AMP, reflecting the distribution of local intrusions in the upper part of the foundation and in the sedimentary cover. The lower level is represented by massive blocks of deep laying and corresponds to the SDR (Seaward Dipping Reflectors) complex, which is an alternation of tectonic plates of continental material with ultrabasite basites that were introduced into the crust at the post-rift stage of the continent’s split. The zone of positive linear anomalies of the magnetic field reflects the divergent boundary of the ancient continental plate of the Baltic, which arose during the fragmentation of the supercontinent of Colombia (Paleopangea) in the middle reef and the formation of the Rifean oceanic basin, which was then veiled by subsequent tectonic processes. The upper structural level indicates the introduction of the main composition into the upper layers of the earth’s crust in the zones of rift-forming faults of magma in late Devonian times during the process of continental rifting on the Svalbard Plate. This is confirmed by the presence of manifestations of the main magmatism within the propagation zone of the South Barents riftogenic depression into the body of the Baltic Shield.Conclusions. The conducted integrated analysis of the anomalous magnetic field and other geological and geophysical data allowed the authors to establish the nature of the sources of magnetic anomalies located at different structural levels of the earth’s crust in the southwestern part of the Barents Sea shelf. The magnetoactive layer of this region is characterized by a complex structure, the section of which includes at least two structural levels, each reflecting certain evolutionary stages of the earth’s crust.

Airborne data processing and 3D modeling of magnetic structures between Nador region and the Chaffarine Islands: Geological significances

The Cap of Trois Fourches-Nador-Chaffarine Islands zone (CTF-N-CI) located in the Moroccan Oriental Rif is recognized by Neogene-Quaternary volcanic outcrops. Those later formed volcanic cones and are considered the main source of the huge Nador magnetic anomaly. This study aims to enhance the magnetic context using geophysical techniques and identify the geometry of magnetic sources by performing 3D modeling using Talwani method. We have achieved the following findings: (1) The elaborated residual magnetic map (Rs) that shows three aligned magnetic anomalies. They are oriented W-E and register a maximum intensity of 380 nT. Applying reduction to the pole to (RTP) the Rs map makes the anomalies on the top of their body sources. Thus, we have found that those anomalies have resulted essentially from the Gourougou volcano and Chaffarine Islands volcanoes outcropping in the study area. Except for the middle Pm anomaly, which is related to volcanic rocks of the Kariate Arekmane drillhole. (2) Performing horizontal derivative (HD) technique leads to establishing the edges of the source bodies. Hence, the inversed map of the magnetization distribution proves that the three bodies are homogeneous and probably splintered from a unique mass. (3) The downward up continuation (DC) to different heights (from 500 to 2000 m) indicates the source's depth. Thus, we have demonstrated that the common source could reach 0.6 km of altitude. (4) Finally, we have constructed a 3D Talwani model of the volcanic edifices. The released 3D model demonstrates that the anomalies are related to a very extensive mass of 80 km in length, 20 km in width, 1.3 km in thickness. This model supports that the Neogene-Quaternary volcanism of the study area was fissural and related to the W-E fracture zone of up to 80 km in length. This volcanism was also affected by the sinistral Nekor fault, which probably made the Trois Fourches Cap body isolated from the other volcanic edifices.Previously mentioned elements probably prove the simultaneous establishment of this large magnetic structure. Moreover, they emphasize the crucial role of the magmatic phenomena which occurred in Northeastern Morocco at the beginning of the Messinian.

Modeling and interpretation of geomagnetic data related to geothermal sources, Northwest of Delijan

Several hot springs and the geology of Northwest of Delijan, Iran, suggest that there is a large geothermal system beneath the area. In 2021, magnetometry methods were used to determine the geothermal structures causing magnetic anomalies of the 300 km2 area surrounding Delijan hot springs. In this research the data are corrected and processed to identify the structural characteristics of the geothermal system in the region and the depth of the geothermal source using the resulting magnetic anomaly maps. After detecting the primary anomalies, the depth and the structural index of the region are estimated using the Euler method. The main source of primary magnetic anomalies in the region is a large pseudo-conical magnetic mass, more the 2000 m deep. The forward model and 3D inversion of data are conducted using ModelVision software and Mag3D computer code, based on the results of the Euler method. The Mag3D is based on the Li-Oldenburg algorithm, by which the best possible solution for magnetic masses is iteratively achieved. The results of modeling and inversion revealed that there is a large magnetic anomaly at 2500–5000 below the surface that is interpreted as a geothermal system source. The results of the current study are in good agreement with the geological information of the region.

Detection of sub-surface fractures based on filtering, modeling, and interpreting aeromagnetic data in the Deng Deng – Garga Sarali area, Eastern Cameroon

Abstract The aeromagnetic anomalies existing in the Deng Deng – Garga Sarali region in Eastern Cameroon were filtered for a structural study of the region’s subsoil. This study presents the results of lineaments and fractures extracted by aeromagnetic image processing methods and compared with scientific data to obtain potential terrain models in the study area. The methodological approach used is based on the filtering of aeromagnetic image by using the analytical signal, the Euler deconvolution, and 2D3/4 modeling, to establish the maps of the lineaments and faults of the study area and their characteristics, and also to propose three models from three previously chosen profiles. Analytical signal and Euler deconvolution techniques have been applied to aeromagnetic anomalies to highlight the relationship between the depth and the source of magnetic anomalies, two parameters whose importance in geoexploration and modeling of the body is essential. We identified the potential contacts by interpretation of the deep Euler anomalies, these are highlighted on the basis of a certain similarity between the maps of the total magnetic field, the map of the analytical signal, the map of the maxima of the gradient horizontal, and geological map. Euler’s map of solutions correlates well with the edges of certain superficial and deep causative bodies.

Ferromagnetism and exchange bias in compressed ilmenite-hematite solid solution as a source of planetary magnetic anomalies.

We propose a compressed ilmenite-hematite solid solution as a new potential source of Earth’s magnetic anomalies. The 0.5FeTiO3·0.5Fe2O3 solid solution compressed by collision synthesis with super-high-energy ball milling showed a decrease in molar volume of approximately 1.8%. Consequently, the sample showed a saturation magnetization of 1.5 ampere square meter per kilogram (Am2/kg) at 300 kelvin, a Curie temperature of 990 kelvin, and a magnetic exchange bias below 100 kelvin, e.g., 1.7 × 105 ampere per meter at 60 kelvin. Ilmenite-hematite solid solutions are common mineral systems in most mafic igneous and metamorphic rocks, and the compressive force in the rocks is generated by the high pressure in the upper mantle or by shock events with high pressure such as the collision of these rocks with meteorites. Therefore, we consider that the compressed ilmenite-hematite solid solution is an additional candidate source of other planetary magnetic anomalies including those in the Moon and Earth.

Petrophysical target characterization with lithogeochemical clustering: the Metsämonttu Zn–Pb–Cu deposit, southern Finland

ABSTRACTIn mineral exploration, reliable and comprehensive petrophysical groundwork helps evaluate the success rate of applying geophysical methods to the target and thus improves the quality of decision‐making related to geophysical surveys. Petrophysical data for potential field exploration can be efficiently collected from drill cores together with portable XRF data that provide insight into rock compositions. We acquired and analysed a multi‐parameter portable‐instrument drill core data set (2036 samples) with portable XRF, magnetic susceptibility and density measurements from the Metsämonttu Zn–Pb–Cu deposit, one of the base metal deposits in the Orijärvi Belt, southern Finland, with little post‐mining exploration during the last 50 years. Our study applied a machine learning technique (Gaussian Mixture Model clustering) to the portable XRF data to provide a pseudo‐lithological reclassification of the drill cores and used this as a basis for characterization of the deposit in petrophysical terms. We also used thermomagnetic measurements to inspect the magnetic mineralogy of the drill cores. Finally, we estimated the success of using potential field methods (magnetic and gravity) for brownfield exploration of analogous deposits in the area. With the portable XRF data clustering we were able to distinguish between barren mafic and felsic volcanic rocks, altered rocks and three different ore mineral enriched rock types. The petrophysical measurement data and thermomagnetic results were combined with the clusters to define the petrophysical characteristics for future mineral exploration with potential field methods. At Metsämonttu, the highest densities are related to the ore and iron sulphide‐bearing rocks. High natural remanent magnetization intensities are related to the iron sulphide‐bearing ore, and remanent magnetization is a significant magnetic anomaly source. Based on synthetic modelling results, both magnetic and gravimetric data could be used in direct exploration in the Metsämonttu area.

Crustal Density and Susceptibility Structure beneath Achankovil Shear Zone, India

Abstract The Southern Granulite Terrain (SGT) is a large tract of exposed Archean continental crust, divided into the Madurai Block (MB), Trivandrum Block (TB), and Nagercoil Block (NB). These crustal domains are linked with the NW-SE trending Achankovil Shear Zone (AKSZ). We combine gravity and magnetic data with previously published ground observations and geochronological data to re-evaluate the crustal architecture, evolution of the AKSZ, and possible extension of AKSZ into Madagascar. Analyses indicate that the long wavelength trends of the magnetic anomalies originate at ~20 km depth of different SGT blocks. These observations are corroborated with the gravity as well as computed gravity gradient anomalies. The presence of khondalite outcrops in Trivandrum Block implies that high magnetization crust is the main source of positive magnetic anomalies. Such magnetic anomalies advocate that SGT preserves the remanent of Archean crustal blocks in South India, a part due to variation in thermal and geochemical processes. The AKSZ, TB, and MB exhibit contrasting magnetic crustal signatures. The joint modeling results reveal a three-layered crustal configuration with varying Moho ranging from 41 to 34 km in NE to SW, respectively. It is also noted that AKSZ is a narrow and deep structure near to the Western Ghats Escarpment while it is wide and shallow in the far-east, which implies that the evolution of the Western Ghats is a late geological event.

D магнитная модель земной коры Белого моря и прилегающих территорий

An important task for the White Sea region, Russia’s second largest diamond-producing province, is the search for magmatic bodies overlapped by sedimentary cover via magnetometer survey. The models, linking local and magnetic anomalies with their sources, are essential for interpretation of search results. The aim of the study is to build a 3D magnetic model of the Earth’s crust for the White Sea region using aeromagnetic data and the modeling technologies of the Integro software package. The simulation is basing on a digital map of the pole-reduced anomalous magnetic field. The sources of magnetic anomalies are believed to be located in the Earth’s crust. The researchers obtained 3D distribution of the relative magnetic susceptibility of rocks by solving the inverse problem of magnetic prospecting. To separate the magnetic sources by spatial frequencies and depth, the model magnetic field was recalculated upward, as well as the TDR derivatives, which determine the lateral boundaries of the sources of positive magnetic field anomalies, were calculated. The researchers further analyzed 2D distributions of the magnetic sources of the model for vertical and horizontal sections with depths of 10, 15 and 20 km, thus proving the relationship between the surface and deep structures of the magnetic sources of the Earth’s crust in the region.

Interpretation for magnetic data at low latitude areas using continuous wavelet transform and marquardt algorithm

As analyzing geomagnetic data at low latitude areas for instance the Mekong Delta (latitudes 11,07o), significant problem is that both of the magnetization and ambient field are not vertical totally, making magnetic anomalies antisymmetrical and often skewed to the location of the sources. In this paper, two-dimensional continuous wavelet transform (2-D CWT), using Farshad-Sailhac complex wavelet function is studied and applied for reducing the magnetic anomaly to a symmetrical one - this located on the source of the anomaly, and then determining the position of the center of the object causing anomalies by wavelet transform modulus maxima (WTMM) method. Next, magnetic data is extracted in two perpendicular directions passing through the center of the source to perform one-dimensional continuous wavelet transform (1-D CWT) to estimate the shape, depth and size of the source. Then, using the Marquardt algorithm to solve the inverse problem by least-squares method to further identify other characteristic parameters of the source such as: vertical size, remanent magnetization vector. The reliability of the proposed method is verified through theoretical models before application for analyzing the geomagnetic data in the Mekong Delta. The results are consistency with deep hole data, having small root mean square error, contribute to a better interpretation of the geological nature of the magnetic anomaly sources in the study area.

Mapping of Kedaton Archaeological Sites Using Geomagnetic Methods (Preliminary Study)

Ancient civilizations in Jombang left many historical relics in the form of temples, artifacts, and other archeological sites. Kedaton site is one of the newly discovered archeological sites. This site is buried under a few meters thick of Mount Kelud’s pyroclastic flow. Therefore, the distribution patterns of the site is needed to improve the excavation plan in order to maintain the structure of the site. One of the technical approaches that can be applied to map the site’s distribution in detail is geophysical survey. Geomagnetic method is a method commonly used in the case of archeological site investigations because of its non-destructive nature. The mapping process on Kedaton site is conducted by applying geomagnetic survey that utilizes physical parameters in the form of magnetic susceptibility. The reduce to pole filter is applied to magnetic data processing to aid interpretation, coupled with horizontal gradient method and analytic signal method further clarify the boundaries of magnetic anomaly sources. Reduce to pole filter indicates that the site’s brick detected as moderate to high magnetic anomaly values (more than 450 nT). This research succeeded in mapping clearly the boundaries of the site with an area of up to 6000 meters2 with the shape of the site resembling a building with several chambers. The main chamber is in the north which is the widest chamber, and small chambers are found on the south side.

Magnetic Structure of the Earth’s Crust in the White Sea Region

The geological structure of the White Sea area and the surrounding land areas has been well studied in the framework of individual case studies. There are a number of local models of the deep structure of the Earth’s crust available. We propose a uniform assessment of deep crustal bodies responsible for long-period (regional) magnetic anomalies and consider their correlation with surface structures. The aim of the study is to build a three-dimensional magnetic model of the Earth’s crust in the White Sea region using aeromagnetic data and modeling technologies of the Integro software package. The model is formed on the basis of a digital map of the anomalous magnetic field reduced to the pole. The sources of magnetic anomalies are considered to be located in the Earth’s crust. The 3D distribution of the relative magnetic susceptibility of rocks was obtained by solving the inverse problem of the magnetic survey. To separate the magnetic sources by frequency and depth, it was necessary to continue the magnetic field of the model upward and to calculate the TDR derivatives, which determine the lateral boundaries of the sources of positive magnetic field anomalies. 2D distributions of magnetic sources of the model for vertical and horizontal sections with depths of 10, 15 and 20 km are analyzed. The correlation between the surface and deep structures of magnetic sources of the Earth’s crust in the region is shown.

Spectral re-evaluation of sediment thickness within Afikpo Basin and environs, southeastern Nigeria, using high resolution aeromagnetic dataset

The discovery of hydrocarbon in the areas bordering Afikpo Basin prompted the re-evaluation of the sedimentary thickness within the basin with high resolution geophysical data. Depth to magnetic sources, sediment thickness, basement topography and structures within it were investigated using spectral analysis, analytic signal and tilt derivative of aeromagnetic data. The results show that the depth to the basement varies between 1.52 and 3.15 km; depth to intermediate magnetic anomaly sources ranges from 0.40 to 1.05 km and depth to the shallow sources varies from 0.10 to 0.34 km. Structures within the basin predominantly have NE-SW trend and the boundary between Afikpo Basin and Southwestern Basement Massif is characterised by NE-SW trending dykes with the longest dyke extending from Amasiri to Abba Omege. The results show that the basin is greatly undulated and the deformation that led to its undulation resulted in the formation of structures which could serve as traps for hydrocarbon accumulation. Sediment thickness greater than 2.3 km associated with some locations within the basin prompted the classification of the places as viable for hydrocarbon formation, if other conditions necessary for its generation are favourable. These places were recommended for further studies for hydrocarbon prospecting on the bases of their sediment structural complexities and thicknesses. Â