Magnetic Source Bodies Research Articles

Volcanic thermal demagnetization of the Reiner Gamma magnetic anomaly

The age and formation mechanism of the Moon's lithospheric magnetic anomalies can give insight into the age and strength of the Moon's past global magnetic field. Here we focus on the magnetic anomaly Reiner Gamma, which is associated with a bright sinuous pattern on the surface known as a lunar swirl. We propose that portions of Reiner Gamma's magnetic source bodies were demagnetized by the heat from volcanic domes in the Marius Hills. We model one of the domes as an intrusive magma body and calculate its subsurface thermal evolution to constrain the volume and burial depth of the original magnetized source bodies. We infer that their burial depths do not exceed ~2 km, which is lower than the basalt thicknesses in this region (~3–4 km) and suggests that the source bodies were emplaced during the Moon's major episode of mare volcanism. The source depths and our inferred magnetization magnitudes are consistent with the magnetic source bodies being magnetized by a strong dynamo on the Moon for at least thousands of years at some point between ~3.5–3.9 Ga. In turn, the implied lack of a strong field during demagnetization implies the Moon's dynamo may have been merely episodically strong, or had permanently weakened at the time of dome formation between ~1.0–3.3 Ga.

Transformation of magnetic data to the pole and vertical dip and a related apparent susceptibility transform: Exact and approximate approaches

The dipolar character of magnetic data means that there is a high and a low associated with each source. The relative positions and sizes of these highs and lows vary depending on the magnetic latitude or the inclination of the earth’s magnetic field. One method for dealing with this complexity is to transform the data to what would be collected if the inclination were vertical (as at the magnetic pole), a process that is unstable at low magnetic latitudes. Unfortunately, remanent magnetization adversely impacts the success of this transformation. A second approach is to calculate the analytic-signal amplitude (ASA) of the data, which creates a single positive feature for each source or edge, with the shape being only weakly dependent on the inclination and the presence of remanent magnetization. The ASA anomalies can appear to be relatively broad, so features sometimes merge together on map views of the ASA. A subsequent transformation of the ASA using an appropriate transforming tilt angle can generate a magnetic field of a body that is at the pole and has a vertical dip. The transformation is exact for contacts when calculated from the first-order ASA, but the sign of the transformed data can be incorrect depending on whether you are over one edge or the other edge of a discrete source body. Another approximate transformation of the zeroth-order ASA does not have this issue and gives good results on synthetic data provided that any noise is handled appropriately. The resulting maps outline the magnetic source bodies and have amplitudes proportional to an apparent magnetic susceptibility. On field data from Black Hill, South Australia, the approximate transformation generates an image that is simple to interpret and enhances some features less obvious on other enhancements of the data.

The Use of Euler Deconvolution Technique in the Estimation of Depth to Magnetic Source Bodies around the Schist Belt Parts of Kano State, Nigeria

Abstract: Depth estimation of magnetic source bodies in parts of the Schist Belt of Kano, using Euler Deconvolution is presented in this paper. Detail ground magnetic survey was carried out using SCINTREX proton precession magnetometer to produce the Total Magnetic Intensity (TMI) map and consequently the residual map. The TMI ranges from 34,261 nT to 34,365 nT, while the residual field ranges from -160 nT to 115 nT. The depth estimate for contacts ranges from 6.5 m to 39.8 m, while that of dyke ranges from 8.9 m to 51.3 m. The depth estimation presented in this work is compared with the results of aeromagnetic study carried out in the same area and found to agree fairly well. Further, this also ensures the validity of aeromagnetic investigation in such applications. Keywords: Contacts, Dykes, Euler Deconvolution, Schist Belt. PACS: 91.25.F and 91.25.Rt.

Predicting Magnetization Directions Using Convolutional Neural Networks

AbstractMagnetic data have been widely used for understanding basin structures, mineral deposit systems, the formation history of various geological systems, and many others. Proper interpretation of magnetic data requires accurate knowledge of total magnetization directions of the source bodies in an area of study. Existing approaches for estimating magnetization directions involve either unstable data processing steps or computationally intensive processes such as 3‐D inversions. In this study, we developed a new method of automatically predicting the magnetization direction of a magnetic source body using convolutional neural networks (CNNs). CNNs have achieved great success in many other applications such as computer vision and seismic image interpretation but have not been used to extract parameters from magnetic data. We simulated many magnetic data maps with different magnetization directions from a synthetic source body, all subject to the same background field. Two CNNs were trained separately, one for predicting the inclination and the other for predicting declination. We determined the optimal CNN architectures for predicting inclinations and declinations by systematically comparing 13 different CNN architectures. In addition, we investigated the effect of having different parameters such as magnetization magnitude, source body shape, location, and depth on the performance of our predictive models. We also tested the method using field data from Black Hill Norite, Australia, and Yeshan region, China, for which prior research results are available for comparison. Our study shows that machine learning provides an effective means of automatically predicting magnetization directions based on magnetic data maps.

ANALYSIS OF HIGH-RESOLUTION AEROMAGNETIC DATA OVER PARTS OF SOKOTO BASIN, NORTH-WEST NIGERIA

Sokoto Basin is one of the sedimentary basins suspected to have high hydrocarbon potential. Hence, due to the possible deposit of this economic mineral, it is worthy of being preliminarily investigated. This paper uses high-resolution aeromagnetic data over parts of Sokoto Basin covering longitude 4.00°E-5.00°E and longitude 12.00°N-13.00°N, to assess the sedimentary thickness beneath the subsurface while also establishing the basement topography. The studied area covered four adjacent one-degree sheets, namely, sheet 27 (Lema), sheet 28 (Argungu), sheet 49 (BirninKebbi) and sheet 50 (Tambuwal). Enhancement of the total magnetic intensity map was carried out to improve the anomaly characteristic of source bodies, and two-dimensional Spectral analysis was carried out using GEOSOFT software (Oasis montaj6.24 version) in order to estimate magnetic source depths in the area. The shallower sources occur at a depth range of 0.23 km - 0.79 km with an average depth of 0.47 km, while the deeper sources occur at a depth range of 0.83 km -1.95 km with an average depth of 1.40 km. The maximum depth to the top of the magnetic source body gets deeper around Lema and IllelaKwandu while the minimum depth is around Tambuwal, Danjema and Birnin-kebbi. Thedepth estimated from the spectral analysis compares reasonably well with the results from the Euler deconvolution. The areas with higher sedimentary thickness toward the northern part of the study area are feasible for hydrocarbon generation and are thus recommended for other geophysical surveys.Keywords: Sokoto Basin, sedimentary thickness, hydrocarbon exploration, high-resolution, aeromagnetic data,geophysical surveys

Gravity constraints on the age and formation of the Moon's Reiner Gamma magnetic anomaly

The Moon once possessed a dynamo that produced numerous magnetic anomalies in the lunar lithosphere. Determining the ages and magnetization strengths of these anomalies would constrain the timing and strength of the dynamo. Unfortunately, most anomalies are not associated with dated geologic features. Here we report that the northeastern portion of the Reiner Gamma magnetic anomaly overlies a relative-negative Bouguer gravity anomaly that we interpret to be a buried impact crater (consistent with Evans et al., 2016). Reiner Gamma is associated with sinuous optical markings known as swirls, which are likely correlated with the underlying magnetization. These markings provide a higher resolution map of the magnetization than possible with existing field data. We present two arguments that suggest the crater overprinted by the Reiner Gamma swirl formed in a pre-existing flood basalt layer. Hence, we constrain the Reiner Gamma source body's age to be bounded by the approximate duration of mare volcanism, ~3.3 Ga to ~3.9 Ga. This range includes the putative high-field epoch of the Moon's dynamo (~3.56–3.9 Ga), which could explain Reiner Gamma's high magnetization. Finally, we calculate the potential range of positions of the rim of the buried crater, and find that the main body of Reiner Gamma is likely outside the buried rim. This finding may be useful for constraining the origin of the Reiner Gamma magnetic source bodies.

Subsurface Structural Mapping over Koton Karifi and Adjoining Areas, Southern Bida Basin, Nigeria, using High-Resolution Aeromagnetic Data

In this current work, we aim to delineate the subsurface structural trends, determine the depth to basement surface, and provide an illustrative 3D model for its subsurface structure. Four digitized aeromagnetic maps were acquired from the Nigerian Geological Survey Agency, Abuja. The total field aeromagnetic anomalies over Koton Karifi and adjoining areas have been evaluated. In order to map the subsurface structures and estimate the depth to basement surface the spectral analysis method was applied. To achieve such goals, a detailed analysis of the aeromagnetic data for the study area was performed. 2D interpretation was carried out for the aeromagnetic data. The processes used include contouring of the Total Magnetic Intensity (TMI) data, separation of regional and residual anomalies, structural detection methods such as analytic signal, vertical derivatives, and magnetic lineament mapping were used to map the contacts and faults within the study area. The first vertical derivative and the magnetic lineament maps show major geologic lineaments trending in East-West with minor ones trending Northeast-Southwest. In the south-eastern part of the study area, there is a dome-shaped linear feature. The result obtained using the spectral analysis method reveals two source depth models. The depths to deeper magnetic sources range from 2.81 km to 3.24 km with an average depth of 2.90 km. The deeper magnetic source bodies are identified with the magnetic basement. The shallower magnetic sources which range from 0.45 km to 1.81 km with an average depth of 1.13 km could be attributed to near surface magnetic sources which are magnetic rocks that intruded into the sedimentary formations or magnetised bodies within the sedimentary cover. Based on the sedimentary thickness range of 0.45 to 3.24 km, there is an indication that the possibility of hydrocarbon generation in the study area is feasible.

Edge detection and magnetic basement depth of Danko area, northwestern Nigeria, from low-latitude aeromagnetic anomaly data

This study aims at estimating depths and boundaries of magnetic source bodies, in order to provide an indirect insight into subsurface geologic features within Danko area of Kebbi state. The study area is located within low magnetic latitude. Hence, the total magnetic intensity anomaly map was reduced to the magnetic equator. This is to center magnetic anomalies over their respective magnetic source bodies, which equally makes the interpretation of sources easier. Matched filtering of the reduced-to-equator (RTE) magnetic anomaly map indicates that the anomalies could be represented by two equivalent layers with some additional noise. The estimated mean depths of burial for the regional and residual sources are 1000 m and 500 m, respectively. Horizontal gradient magnitude and tilt derivative methods carried out on the RTE aeromagnetic anomaly map facilitated the identification of two distinct geologic trends bounded by a prominent fault suspected to be the documented Yelwa fault. Furthermore, the analytic signal map showed magnetic basement depth values between 50 and 900 m with an average value of 475 m, indicating a compelling alignment of results with the 500 m depth value for the residual matched filter layer. Several mineral occurrences have been found within the outcropping basement rocks of the study area. Hence, the combined appraisal of source edge locations and magnetic basement depth estimates offers useful information of the underlying basement configuration, which is highly essential for mineral exploration targets that are mostly obscured by regolith cover.

English

This study aimed to estimate the depth of magnetic source bodies in Lafia and Akiri areas which fall within the middle Benue trough, Nigeria. Aeromagnetic data were used and spectral analysis and source parameter imaging were used for the quantitative interpretation of the data. The total magnetic intensity (TMI) contour map obtained from gridding of the data ranging from -39.5 to 100.0 nT was separated into regional and residual contour maps; it was done by polynomial fitting to produce the residual aeromagnetic intensity contour map. The residual intensity varies from -78.9 to 55.0 nT while the regional intensity varies from -39.18 to 39.84 nT. Depth results obtained from spectral analysis revealed two depth sources: the shallower magnetic source bodies and the deeper magnetic source bodies. The depth of shallower magnetic sources ranges from 0.557 to 1.261 km, with an average depth value of 0.899 km, whereas the depth of deeper magnetic sources varies from 2.419 to 5.732 km with an average depth value of 4.105 km. The SPI depth result ranges from -0.5638 km (shallow magnetic bodies) to 5.8381 km (deep lying magnetic bodies). The two methods showed depth estimation within the same range. The sedimentary thickness obtained from the different methods indicates the possibility of hydrocarbon accumulation if other conditions for hydrocarbon generation are satisfied. Key words: Magnetic source bodies, depth estimation, spectral analysis, SPI, Lafia and Akiri areas, aeromagnetic data.

A small lunar swirl and its implications for the formation of the Reiner Gamma magnetic anomaly

The Moon does not currently possess a dynamo, but its crust contains numerous magnetic anomalies detected from orbit. The geologic origins of these anomalies are still unknown, including the archetypal Reiner Gamma magnetic anomaly. To gain insight, we study a small magnetic anomaly, herein called the octopus, which is possibly associated with Reiner Gamma. The octopus has curving bright albedo patterns characteristic of features known as swirls. We use high cadence 9 Hz Lunar Prospector magnetometer data, along with constraints provided by this swirl's albedo pattern, to perform inversions for the swirl's magnetic source body characteristics. We use three different inversion methods, and they all return similar results. We also estimate the depth of magnetization from characteristics of the horizontal component of the magnetic field and the albedo pattern. We find that performing inversion for source body properties at small swirls has advantages compared to larger anomalies, or anomalies without albedo markings. We find the octopus is magnetized in the same direction as the main Reiner Gamma anomaly (within 1σ uncertainties), suggesting they formed contemporaneously. The large spatial distance between these coeval anomalies and their inferred shallow source body depths are compatible with formation in a hot ejecta deposit that cooled in the presence of a dynamo field, as suggested by Hood et al. (2001). However, a key remaining enigma is why the northeastern Reiner Gamma “tail” formation has a magnetization direction ∼60° different from the main body and octopus.

New geophysical data from a key region in East Antarctica: Estimates for the spatial extent of the Tonian Oceanic Arc Super Terrane (TOAST)

Within Antarctica, eastern Dronning Maud Land (DML) represents a key region for improving our understanding of crustal fragments that were involved in the amalgamation and breakup histories of Rodinia and Gondwana. An aerogeophysical survey was flown during the austral summers 2013/14 and 2014/15 to explore the largely ice-covered region south and east of Sør Rondane. Here, we present 40,000 new line kilometer of aeromagnetic data gathered across an area of ca. 295,000km2 with a 10km line spacing. Magnetic domains, major lineaments, locations, and depths of magnetic source bodies are detected from total field data, their tilt derivative, pseudo-gravity, and analytical signal transformations, and from Euler Deconvolution maps. These data are integrated with exposure information from the Sør Rondane, Belgica and the Yamato mountains in order to identify the eastern spatial extent of a major juvenile Early Neoproterozoic crustal province, the Tonian Oceanic Arc Super Terrane (TOAST). Magnetic data reveal a characteristic pattern with NW-SE trending elongated magnetic anomalies to the south of Sør Rondane. This area is interpreted as the eastward continuation of the distinct SE DML Province and therefore of the TOAST. Major curvilinear magnetic anomalies of several hundreds of kilometers length dissect the region south and southwest of Sør Rondane. These may represent boundaries of individual oceanic arc terrane or alternatively major Pan-African shear zones. A significant change of the magnetic anomaly pattern ca. 800km inland of Sør Rondane may indicate the southern minimum extent of the TOAST. Magnetic anomalies of varying size, amplitude, and orientation suggest a complex transitional area between the Belgica and Yamato Mts., which appears to separate the TOAST from an Indo-Antarctic craton to the east. The new data suggest that the TOAST is comparable in size with the Antarctic Peninsula and therefore represents a significant piece of Neoproterozoic crustal addition. It originated at the periphery or outboard of Rodinia and is a remnant of the Mozambique Ocean.

Integrated Geophysical Study to Delineate Mineralised Zones in Southwest Ashanti Belt of Ghana

Ground Frequency Domain Electromagnetic (FDEM) and Magnetic surveys were conducted in Southwest of the Ashanti belt in the Western Region of Ghana. The aim was to delineate potential gold mineralisation zones that may occur within the area. The magnetic data processing steps involved analytic signal, first vertical derivative, upward continuation, CET grid analysis as well as depth to basement model (Werner deconvolution). For the electromagnetic survey using the two coil separations (100 m and 150 m) and the multi frequencies (222 Hz, 888 Hz, 3555 Hz), the data in-phase component was processed to produce EM component maps showing the potential mineralisation zones. Lineament analysis using the rose diagram showed that the area is dominated by N-S and NNW-SSE lineaments. The upward continuation and depth to the magnetic source bodies indicated that the magnetic bodies in the study area can be located at depth less than 200 m.

Magnetic mineral exploration using ground magnetic survey data of Tajimi Area, Lokoja

Ground magnetic survey is an essential geophysical method employed in locating subsurface magnetic materials for possible exploration. In geophysics, the anomalous magnetization might be associated with local mineralization that is potentially of commercial interest. Hence a ground magnetic survey was carried out at a site in Tajimi area of Lokoja, Kogi State, Nigeria. The study is aimed at locating the position of iron deposited minerals within the study area. The study area lies within Latitude 8 0 0292ˈN to 8 0 0625ˈN and Longitude 6 0 5833ˈE to 6 0 6167ˈE in the basement complex of Southern Nigeria. A total of fifteen magnetic transverse lines were established in an E-W direction in the study area covering 140m by 75m. Data were taken and recorded using Proton Precession magnetometer; the data were presented in magnetic profiles, 2D contour map and 3D surface map which aided the qualitatively interpretation. The study area was characterized by completely varying magnetic anomaly amplitudes across the field. The field data were quantitatively interpreted and the results gave values for the total component measurements of the ground magnetic anomaly that varied between a minimum negative peak value of about -23428.7nT and a maximum positive peak value of about 5840.9nT. The residual anomalies obtained were plotted against distance using Microsoft Excel and Analytic signal method was used to estimates the depth to the magnetic source body. The estimated depths of the magnetic source body/rocks from the Earth surface fall in the interval of 1.28m to 13.57m, which indicates the magnetic source body suspected to be magnetic mineral, are near surface features. Hence a careful analysis of the magnetic anomaly maps can give vital information about the magnetic distribution and mineral potential of the study area at Tajimi.

English

Structural interpretation of aeromagnetic data over Nkalagu-Igumale area of the Lower Benue Trough of Nigeria was carried out to determine the depth to magnetic basement and delineate the basement morphology and the structural features associated with the basin and their trends. The aeromagnetic data were subjected to series of computer based image and data enhancement techniques before spectral analysis. Results of the 2-D spectral analysis revealed two depths source models with the depth model (D1) for deep magnetic source bodies which are associated with intra-basement discontinuities and faults ranging from 2.15 to 5.25 km while the depth model (D2) of the shallow magnetic source bodies range from 0.35 to 0.99 km. From an economic viewpoint, the results indicate possible mineralization and existence of a reasonable Cretaceous sedimentary thickness in the area which is deep enough for hydrocarbon accumulation. The average sedimentary thickness obtained in the area is 3.75 km. Key words: Benue Trough, depth to magnetic basement, aeromagnetic data, spectral analysis, intrusive bodies.

Estimation of depth to magnetic source bodies of Nsukka and Udi areas using spectral analysis approach

The study was aimed at estimating the depth to magnetic source bodies in Nsukka and Udi areas which falls within the Anambra basin. Aeromagnetic data were used and Spectral Analysis approach was employed in the quantitative interpretation. The total magnetic intensity (TMI) contour map which ranges from -53.1 to 133.7 nanoTesla (nT) was separated into regional and residual contour maps to produce a residual aeromagnetic intensity contour map. The residual intensity varies from -51.2 to 59.6 nT while the regional intensity varies from -8.7 to 85.1 nT. Depth results obtained from spectral analysis revealed two depth sources; the shallower magnetic source bodies and the deeper magnetic source bodies. The depth of shallower magnetic sources ranges from 314.12 to 1061.05 m with an average depth value of 632.32 m, whereas the depth of deeper magnetic sources vary from 1465.90 to 5888.73 m with an average depth value of 3260.41 m. Key words: Magnetic source bodies, depth estimation, spectral analysis, Nsukka and Udi areas, aeromagnetic data

Forward and Inverse Modeling of Hand Digitized Aeromagnetic Data from Ilesha South West, Nigeria

Results of aeromagnetic data interpretation of Ilesha SW, Nigeria are presented here. The geology of Ilesha which is Precambrian falls under the basement complex of Nigeria. Depths to source rocks in this area are expected to be shallow. The results obtained revealed the presence of rocks such as amphibolites, quartz and schist which are the common rock types present in the study area. An aeromagnetic map of scale 1:50,000 was hand digitized, while forward and inverse modeling was achieved via the use of Potent, version 4.10.02. The field data were qualitatively and quantitatively interpreted and results showed NE-SW trending of the fault zone in the study area and anomalous bodies whose total magnetic intensity ranges from a minimum negative peak value of -625.5 nT to a maximum positive peak value of 179.43 nT. The maximum depth to top of the magnetic source body obtained is 34.2 m and minimum depth is 0.5 m. The results obtained indicate shallow depths to magnetic anomalies, as expected in most areas of the basement complex of Nigeria.

Magnetic Basement Depth Re-Evaluation of Naraguta and Environs North Central Nigeria, Using 3-D Euler Deconvolution

This paper presents a detailed geological interpretation of the aeromagnetic data over Naraguta and environs using 2-D spectral inversion and 3-D Euler deconvolution techniques. The objectives of the study are to re-evaluate the depth to the magnetic basement and to delineate associated structural features in the study area. Data enhancement was carried out to separate residual features relative to the strong regional gradients and the more intense anomalies due to basement features and igneous intrusives. Results of the 2-D spectral analysis revealed a two layer depth source model. The deeper magnetic source bodies (d<SUB>2</SUB>) varies from 1.672km to 2.3km with an average depth of 1.999km while the depth to the shallower magnetic source bodies (d<SUB>1</SUB>) ranges from 0.55km to 0.897km with an average depth of 0.711km. The shallower magnetic anomalies are believed to be as the result of basement rocks which intruded into the sedimentary rocks while the deeper layer may be attributed to magnetic basement surface and intra-basement discontinuities like faults, fractures and lineations. Structural analysis of these shallow anomalies using 3-D Euler deconvolution with structural index values ranging from 0-3, revealed three main structural models which include spheres, horizontal pipes/cylinders and sills/ dikes. Similarly, magnetic basement depth estimates using 3-D Euler deconvolution revealed a magnetic basement depth range of 0.5 - 2.5km. Finally, the average sedimentary thickness of 1.999km estimated from the study area is unfavorable for hydrocarbon generation and accumulation. However, the area is more viable for solid mineral exploitation based on the presence of several intrusive and linear features which may have acted as conduits for mineralization.

Crustal architecture of the Thomson Orogen in Queensland inferred from potential field forward modelling

The basement rocks of the poorly understood Thomson Orogen are concealed by mid-Paleozoic to Upper Cretaceous intra-continental basins and direct information about the orogen is gleaned from sparse geological data. Constrained potential field forward modelling has been undertaken to highlight key features and resolve deeply sourced anomalies within the Thomson Orogen. The Thomson Orogen is characterised by long-wavelength and low-amplitude geophysical anomalies when compared with the northern and western Precambrian terranes of the Australian continent. Prominent NE- and NW-trending gravity anomalies reflect the fault architecture of the region. High-intensity Bouguer gravity anomalies correlate with shallow basement rocks. Bouguer gravity anomalies below –300 µm/s2 define the distribution of the Devonian Adavale Basin and associated troughs. The magnetic grid shows smooth textures, punctuated by short-wavelength, high-intensity anomalies that indicate magnetic contribution at different crustal levels. It is interpreted that meta-sedimentary basement rocks of the Thomson Orogen, intersected in several drill holes, are representative of a seismically non-reflective and non-magnetic upper basement. Short-wavelength, high-intensity magnetic source bodies and colocated negative Bouguer gravity responses are interpreted to represent shallow granitic intrusions. Long-wavelength magnetic anomalies are inferred to reflect the topography of a seismically reflective and magnetic lower basement. Potential field forward modelling indicates that the Thomson Orogen might be a single terrane. We interpret that the lower basement consists of attenuated Precambrian and mafic enriched continental crust, which differs from the oceanic crust of the Lachlan Orogen further south.

Constraint on subsurface structures beneath Reiner Gamma on the Moon using the Kaguya Lunar Radar Sounder

Reiner Gamma is a sinuous feature in Oceanus Procellarum; it has a higher reflectance of the visible wavelength than the surrounding flat mare basalt, and displays a high crustal magnetic field. Previous studies relating to the origin of Reiner Gamma have provided contradictory depths of magnetic source bodies in the lunar crust as either shallow or deep. If a shallow ejecta layer existed beneath the Reiner Gamma formation, a subsurface lithological boundary between the denser mare basalt and the less dense ejecta blanket would be expected. This study examines subsurface stratifications using the Lunar Radar Sounder (LRS) onboard the Kaguya spacecraft. Taking into account the LRS-determined dielectric constants, the influence of surface clutter, and the energy loss of the LRS radar pulses in the high frequency band (5MHz), no evidence was found of subsurface boundaries down to a depth of 1000-m at Reiner Gamma. Given the LRS range resolution of 75-m, the source of the magnetic anomaly is considered to be either strongly magnetized thin breccia layers at depths shallower than 75-m, or less magnetized thick layers at depths deeper than 1000-m.

2-D Spectral Analysis of Aeromagnetic Anomalies over Parts of Monguno and Environs, Northeastern Nigeria

2-D Spectral Analysis of aeromagnetic anomalies over parts of Monguno and environs, northeastern Nigeria was carried out to determine the depth to basement, establish the basement topography and determine the temperature at depths in the area. Data enhancement was carried out to delineate residual features and the more intense anomalies relative to the strong regional gradients. Typical techniques applied were computations of reduction to pole, trend surface analysis, and a number of filtering processes. Results of the 2-D spectral analysis of the aeromagnetic data revealed a two depth source model. The depth to the deeper magnetic source bodies ranges from 1.22 to 3.14 km, with an average depth of 2.341 km. This layer may be attributed to magnetic rocks of the basement, lateral variations in basement susceptibilities and intra- basement features like faults and fractures. The shallower magnetic sources range in depth from 0.12 to 0.93 km, with an average depth of 0.572 km and could be attributed to near surface magnetic sources, which are magnetic rocks that intruded into the sedimentary formations. Based on the computed average sediment thickness obtained in this study together with the temperature at depths in the area, some parts of the study area have been demarcated for detail hydrocarbon exploration in-line with the renewed interest in hydrocarbon exploration in the basin.