High-resolution Aeromagnetic Data Research Articles

Geothermal prospective areas in the Northern sector of Bida Basin and environs, North-Central Nigeria

With the deteriorating electrical power supply in Nigeria, it is imperative that more alternative sources are explored. This research work is carried out to assess part of the Bida basin as a possible source of geothermal energy that will help to augment the electric power generation in the country. The study was carried out within the northern sector of the Bida Basin and environs and the area which lies between Longitudes 5000ʹ00ʺ – 7000ʹ00ʺ E and Latitudes 8030ʹ00ʺ – 10030ʹ00ʺ N. Sixteen (16) half degree high resolution aeromagnetic data in a block grid format was utilised for this research. To enhance data for interpretation the total magnetic intensity (TMI) map was subjected to regional-residual separation using Oasis Montaj (version 7.0.1) software. To minimize the effect of frequency noise caused by tiny structures near ground surface, the residual magnetic map was upward continued and further divided into sixteen square blocks with each block windowed and subjected to spectral analysis using Matlab (version R2010a) software. Surfer 11 surface mapping software was used for data contouring. Results obtained from the analysis revealed a Curie point depths ranges from 9 – 17 km over the study area, a geothermal gradient range from 32 – 65 0C km-1, and heat flow ranges from 83 – 163 mWm-2. From interpretation of heat flow map, the prospective areas with anomalous geothermal conditions recommended for geothermal exploitation are areas around Masamagu, Mokwa, Bokani, Lapai, Agaie and Agena.

Upward continuation of total magnetic field intensity data over Sokoto basin, north-western Nigeria

High-resolution aeromagnetic data covering the Sokoto basin, north-western Nigeria were acquired and analyzed using regional enhancement techniques, upward continuation and second order regional. The objective was to delineate major geological structures. The data, which are in form of a grid, were knitted using Oasis Montaj software to obtain the magnetic total field intensity map. The composite grid was reduced to a magnetic equator to align the peaks of magnetic anomalies over the center of their causative bodies. The reduced grid was continued at various planes of observation to understate anomalies due to shallow features. The planes were at 10 km, 20 km, 30 km, 40 km, 50 km, 70 km, and 100 km above the surface. Upward continuation maps produced greatly enhanced the long-wavelength (low wavenumber) anomalies associated with deeper subsurface regional structures. The continuation revealed a high magnetic intensity anomaly in western parts of the area and low magnetic intensity anomalies in the eastern parts. The low magnetic intensity in the eastern part is interpreted as a sedimentary deposit. The residual field was removed from the total magnetic field data using the second-order least square method to get the second-order regional field. The regional field analysis agrees with the upward continuation result.

Noise Reduction of Aeromagnetic Data Using Artificial Neural Network

The high-frequency content of high-resolution aeromagnetic data is of particular interest to geophysic ists to identify mineral deposits, shallow faults, and dikes. However, high-resolution aeromagnetic data is contaminated by cultural noise generated from aircraft and man-made features. The culture noise must be removed before starting the interpretation process. Manual techniques are more selective of the noise; however slower and more expensive because they require considerable hands-on interaction. The present study develops a novel method for detecting and removing the culture noise from aeromagnetic data based on an artificial neural network (ANN) in an automatic way and comparing the results with a conventional algorithm using the nonlinear filter. The proposed method is tested using a theoretical example that combine a magnetic anomaly due to a dyke with three sources of cultural noise, besides using a practical example to increase the number of training pattern. The network is trained based on the backpropagation training function, where the algorithm updates the weight and bias states as per the Levenberg–Marquardt optimization. The optimization is reached during the training and validation process after 3,000 iterations. The correlation coefficient ( R) is utilized along with the mean squared error (MSE) as performance indices of the ANN. The ANN demonstrates the capability to detect the spiky data based on the optimal weights, thus allowing for removing and replacing them with clean data using the piecewise cubic Hermite interpolating polynomial (PCHIP) function. The practical utility of the two-method is discussed using high-resolution aeromagnetic data from the Tushka area located in the southwestern desert of Egypt. Comparing the denoising results using the two methods shows that the current approach is more effective in processing and more closely recovering the original magnetic data.

Application of Aeromagnetic Data Analysis and Interpretations to Investigate Solid Mineral Potential in Part of Bauchi, Northeast Nigeria

Abstract: The distribution of surface and subsurface magnetic materials within the study area, the delineation of geologic lineaments, and an estimate of the depth to magnetic sources were all determined by interpreting high resolution aeromagnetic data that covered a portion of Bauchi, northeastern Nigeria, lying between Latitudes 9040'00"N to 10010'0"N and Longitudes 900'0"E to 9040'0'E. The Aeromagnetic map, analytical signal, and horizontal derivative filters used on total magnetic intensity data after reduction to the magnetic equator (RTE) show that the Toro and its environs contain highly magnetic minerals thought to be potential deposits of iron ore. The lithological map and the lineament maps have a good connection. Further examination of the findings reveals that the research area has varying degrees of Ferro-, para-, and diamagnetic mineralization (of the iron and non-iron varieties). The geological source bodies are thought to be located between 177.389 and 991.626 meters deep, according to the Euler depth solution. This shows that during the orogenic process, a sequence of strong deformations were present alongside the Toro.

Subsurface Structural Characterization as Deduced from High-Resolution Aeromagnetic Data over The Confluence Zones in Central, Nigeria

This study aimed to delineate the intrusion body that controls the structural setting and formation around the river Niger-Benue confluence zone with particular attention to its solid mineral potentials, this is achieved in mapping subsurface structural features through the analysis of recent high-resolution aeromagnetic (HRAM) data-sets with the purpose of examining their effects on geological structures that characterize the confluence zones from the study area. To obtain the necessary reduction in geomagnetic variation, measurements of regional gradients and time variation were used. After applying the reduction to the magnetic equator (RTE) to the corrected magnetic data that was obtained from the Nigerian Geological Survey Agency, NGSA, it was possible to determine the regional expansions of subsurface structural units for both qualitative and quantitative interpretations. In addition, the edge detection method is used to depict the structures and buried subsurface anomalies. Different handling processes were applied to the (HRAM) data, such as local wavenumber (SPI), power spectrum analysis, and Euler and Werner deconvolution analysis. The RTE magnetic anomaly caused by local structures and anomalous body delineated six sub-basins with low amplitude response, which agrees with the total gradient anomaly (analytic signal) and tilt of angle derivative that clearly outlined and characterize edges of lithostratigraphic of Niger-Benue river confluence zones. The sub-basin delineated are the southern Bida basin and northern Anambra basin. The source parameter imagings as well as the Euler and Werner deconvolution were used to delineate major subsurface structures and determine their source depth. Results showed that the area was affected by different lineament trending NE-SW, E-W, and S-E trends. Directional analysis indicates that the dominant trend agrees with the regional fault orientations. The estimated depth to the top of the lineaments on average varies from 0.3 km to 4.6 km and it is relatively deeper in the basins compared to the surrounding areas giving clues to the amount of sediment infill. A 2D forward model showed a sedimentary thickness ranging from 1 to 7 km, and this estimated depth is consistent with the average of 3.5 km proposed by previous researchers.

Delineation of source magnetization and subsurface discontinuity of Ririwai Ring Complex along Kano, North Western Nigeria

High Resolution Aeromagnetic (HRAM) data of Ririwai (sheet 126) which lies between latitude 10° 30' to 11° 00' N and longitude 8° 30' E to 9° 00' E, was used for this research. The study area, Ririwai is situated along Kano, in the Northwestern part of Nigeria, both qualitative and quantitative interpretation techniques were employed in this study. This procedure was carefully undertaken by employing enhancement filters; vertical derivative, upward continuation, analytical signal amplitude processing, and quantitative approaches such as Euler 3D deconvolution and an apparent susceptibility filter to help further give solutions for depth estimates and magnetization. The Euler deconvolution was able to show that the solution plotted clustered around the region where the geological structures are located with average depths range of <139.8 to >904.5 m, with very few solutions having depths less than 200 m, the most prominent structure particularly the Ririwai ring complex have a depth range of 182.9 to 301.5 m. The magnetic susceptibility reading obtained shows that the area is composed of rocks high in magnetic minerals such as magnetite along the western end of the area, it is also flanked by medium to high magnetic values around the central parts with only regions of low magnetic values predominantly along the Ririwai complex and its adjoining outcrops towards the eastern half of the area under study.

INTERPRETATION OF HIGH RESOLUTION AEROMAGNETIC AND LAND SATELLITE IMAGE OVER PART OF THE NORTH-CENTRAL BASEMENT COMPLEX: IMPLICATION FOR GROUNDWATER EXPLORATION

Considering the significance of groundwater to population growth, this study interprets high resolution aeromagnetic and land satellite imagery data to explore prospective areas for groundwater occurrence in part of the north-central Basement Complex of Nigeria. The study area lies between longitudes 5030' – 7000' E and latitudes 9030' – 10030' N. To achieve this objective, high resolution aeromagnetic data covering the study area was subjected to magnetic residual separation and analytical signal using Oasis Montaj version 8.4. The Land satellite imagery data was also subjected to false colour composite analysis using ILWISversion 3.3 software. Combination of this analysis aided in mapping of lineaments within the study area. Result of lineaments mapping from analytical signal and land satellite images shows high density lineaments around Wushishi, Zungeru, Tegina Kagara, Pandogari, Alawa, Gurmana and low density lineaments around Bobi, Kuta, Guni, Minna, Tenenge. These lineaments having a dominant trend in the NE-SW and NW-SE, E-W minor directions were interpreted as joints, veins, faults, foliations and lineation of outcrops. Field studies in Tegina, Zungeru and Wushishi falling within areas with high lineament density revealed good groundwater yield from motorized pumps, hand pumps and hand dug wells. This is contrary to what was observed in Gidan Gwari an area attributed to low lineament density where only one hand bore hole out of the seven drilled boreholes was productive.

Using geophysics to follow and model the Precambrian basement terranes beneath the Caledonian nappes in Finnmark, northern Norway: A case study

The bedrock geology of Finnmark, northern Norway, consists primarily of rock complexes dating back to the Precambrian and early Mid Palaeozoic eras and comprises (1) a mid-crustal lithospheric basement which is characterised by granitoid and greenstone complexes dating from Neoarchean to late Paleoproterozoic in age; (2) the Caledonide Orogen, characterised by a series of nappes and thrust sheets. Finnmark forms part of the northern margin of the Fennoscandian Shield, which extends across northern Finland into northwestern Russia. Precambrian rock complexes are also found as thrust slices in Caledonian nappes at several places in Finnmark and Troms, as well as in tectonic windows.Recently acquired high-resolution aeromagnetic data have provided spectacular and confirmatory evidence for the continuation of the diverse Precambrian greenstone belts and granulite terranes beneath the magnetically transparent Caledonian nappes.This study aims at analysing this subsurface continuation of the terranes using potential field data and estimating the depths of the main magnetic sources beneath the nappes. In this study, several geophysical methods are used, including 3D Euler deconvolution and 2D Werner deconvolution. We have focused specifically on the depth-to-basement beneath nappes and purposefully excluded anomalies associated with shallow structures, such as dykes and faults. Different methods have produced similar results and indicate an appreciable increase in the depth of the Precambrian basement rocks from south to north. In the south, Precambrian basement rocks are either exposed on the surface southeast of the Caledonian front or reappear within tectonic windows. A prominent positive magnetic anomaly on the Porsanger Peninsula is thought to represent an extension of the anomaly ascribed to the greenstone belt of the Repparfjord Tectonic Window. A 3D model of this has also been provided. According to estimates, the depths-to-basement below nappes close to the Caledonian front range from less than 500 to 2000 m, whilst in the northern part of the study area the depths generally reach 3000 to 4000 m, and are locally estimated to range between 5000 m and 6000 m.

Concealed anatomy and new geological features beneath desert areas of NW India – Constrained from high resolution aero-geophysical data

The vast swathe of area in the Trans-Aravalli region between the western part of the South Delhi Fold Belt and eastern part of the Barmer basin, north-western India exhibits limited geological information due to thick sand cover of the Thar Desert. The present study is to unravel the hidden architecture of the above area using recently acquired high-resolution aero-magnetic data. Here, our interpreted results brought out a buried ring structure in the northern part and NW-SE trending constellation of linear magnetic highs in the southern part. Considering the regional geological milieu, our study correlates the buried ring structure with a possible remnant volcanic cone of the Neoproterozoic silicic Malani Large Igneous Province. Secondly, the significant NW-SE trending linear magnetic highs in the south possibly represents a humongous dyke swarm activity, facilitated by the intricate network of fractures. The orientation of these magnetic linear are conspicuously similar with the Deccan linked Sarnu-Dandali dykes and regional Barmer-Cambay rift system. The northwestern portion of study area displays high magnetic and gravity responses of long wavelength features indicating crustal heterogeneity. The study for the first time documents two concealed structures, which may hold a link of Neoproterozoic Malani and Mesozoic Deccan magmatic pulses.

Multithematic Geoscience Data Integration for Identification of Mineral Potential Areas in Parts of Central Indian Precambrian Craton

Abstract The paper highlights the results of multi-thematic geoscience data integration involving geological, geophysical, geochemical and remote sensing data sets, for an area of 4000 Sq. Km in parts of Precambrian Bastar craton, Chhattisgarh. The present team has been able to identify two discrete mineral potential areas for base metal sulphides, Sn, W and REE in sheared and altered felsic volcanics in Kotra-Bhansula area and for gold in propylitically altered meta basalts in Bhursatola-Khampura area. The dataset utilized during collation and integration includes (i) high resolution aeromagnetic data (ii) 1:50000 geological data covering litho-structural and mineralisation attributes (iii) 1:50 k geochemical data for 61 elements (iv) multispectral ASTER satellite data and its derivative alteration maps. Thematic data and derivative maps were studied and interpreted for evaluation of concerned parameters for estimating their role in mineralisation. The data integration has been implemented in three steps beginning with GIS based spatial modelling using Fuzzy logic method resulting into production of mineral favourability map, followed by detailed field evaluation and characterization of the identified mineral favourability areas. Eventual identification of potential areas was based on synthesis of modelling output, field outcome and laboratory results of analyses carried out on critical samples collected from mineral favourability areas. The identified two mineral potential areas are recommended for further detailed exploration for gold, base metal, Sn, W and REE through surface and sub-surface probing.

Application of scaling geology in magnetic basement mapping around the Middle Benue Trough in Northcentral Nigeria

Using the scaling spectral method applied on high resolution aeromagnetic data, we mapped the magnetic basement and estimated the scaling exponents across various lithologies within the Middle Benue Trough of Northcentral Nigeria. We estimated a depth range of 1.8–6.3 km, with an average of 3.7 km to the basement beneath the Cretaceous sediments of the trough. Shallow basement depths of <3 km are mostly found on the trough's northern and southeastern margins. These are uplifted Precambrian Basement Complex regions made up of older granite, gneiss, and migmatite. Deeper basement depths of >4 km predominate in the southwestern, central, and northeastern portions of the study area, trending along the trough's axis. These deep zones are filled with Cretaceous sediments that must have accumulated after the Mesozoic development of the Benue Trough's subsided graben structure. Our study estimated scaling exponent ranging from 0 to 2. There were some correlations with the geology of the area, particularly around the crystalline basement complex in the northern portion. Within the central portion of the Middle Benue Trough, however, the source distributions are less correlated, uneven, and not always consistent with the geology of the area. This could be due to the region's dynamic and unstable tectonics, as numerous magmatic intrusions have been emplaced into the Cretaceous sediments at various depths, potentially influencing the scaling exponent values.

Targeting Paleovalley-Related Ferricrete Units in Yilgarn Craton Using High-Resolution Aeromagnetic Data and Spatial Machine Learning

The ferricrete units (Fe oxide cemented colluvial-alluvial sediment) of the Yilgarn Craton in Western Australia formed during the humid tropical and sub-tropical climates of the Cenozoic. Ferricretes are generally developed on long-lived paleodrainage systems and are products of the ferruginisation of detritus provided by the continuous erosion of upslopes. These iron-rich accumulations can become Au-enriched, as is the case in several locations previously discovered in the Yilgarn Craton; many of these host economic secondary gold deposits (e.g., Moolart Well, Mt Gibson, and Bulchina), typically occurring downslope of low saprolite hills and near paleovalleys (i.e., inset-valleys). Inset-valleys are a common paleotopographic feature buried under Quaternary alluvial and colluvial sedimentary cover. Maps of these ancient channel networks can be used as a proxy for targeting ferricrete gold deposits. These inset-valley systems generally form dendritic and noisy patterns in high-resolution aeromagnetic data due to the presence of maghemite-rich nodules and detrital magnetic pisoliths on their flanks. The main aim of this study was to use high-resolution aeromagnetic data to target ferricrete units related to inset-valleys systems across the Yilgarn Craton. A spatial predictive model was used to learn and predict the geological units of interest from pre-processed aeromagnetic data. The predicted inset-valleys systems were able to confine the exploration space and define a new exploration frontier for ferricrete gold deposits.

The 180-km-long Meers-Willow fault system in the Southern Oklahoma Aulacogen: A potential U.S. mid-continent seismic hazard

Abstract We integrate new high-resolution aeromagnetic data with seismic reflection data, well logs, satellite remote sensing, and field observations to provide a regional view of buried and exposed structures in the Southern Oklahoma Aulacogen and to assess their potential for future seismicity. Trends ranging from NW–SE to ~E–W, peaking at 330° ± 4.5° and 280° ± 3°, dominate the magnetic lineaments of the Southern Oklahoma Aulacogen, reflecting basement contacts, dikes, and faults, including a previously unmapped ~100-km-long basement fault, which is herein referred to as the Willow fault. The fault disrupts, truncates, and vertically offsets basement-related seismic reflectors and overlying Paleozoic strata up through the Permian reflectors. Surface deformation along the trend includes fault-parallel monoclinal folds, pervasive fractures, and fracture-hosted mud dikes in Permian evaporite units. These structures indicate a Permian or post-Permian reactivation of the fault. Along-strike, the Willow fault connects to the NW-trending, seismically active Meers Fault to comprise the ~180-km-long Meers-Willow fault system, which potentially represents a major seismic hazard along the Southern Oklahoma Aulacogen. Fault slip potential analyses of the mapped potential fault traces show that seismic hazards are elevated where faults have steeper dips. Given some uncertainty in the regional stress state, we also show that hazards along the NW–SE to E–W trending faults vary considerably within the uncertainty range. We propose that the Meers-Willow fault system originated as a Cambrian aulacogen-scale, basement-rooted fault that was later reactivated as a left-lateral strike-slip fault (with ~40 km displacement) during the late Paleozoic Ancestral Rocky Mountain orogeny, highlighting that lateral offset accommodated a major component of deformation during the orogen.

Reconnaissance investigation of geothermal resources in parts of the Middle Benue Trough, Nigeria using remote sensing and geophysical methods

In Nigeria, the basement complex and the sedimentary basins house many thermal springs which are physical manifestations of geothermal energy. However, there are difficulties in accessing the sustainability of these resources due to ethical and security issues as well as limited data in Nigeria. Thus, identifying the precise location, temperature, and energy potential on a large scale has been a major drawback.This paper is the preliminary investigation of geothermal potential in parts of the Middle Benue Trough using satellite imagery, geology, regional gravity, and high-resolution aeromagnetic data. Landsat 8 scene was used to estimate the Land Surface Temperature (LST) in ArcGIS™. Selected sites were classified as very low, low, moderate, and high LST. The intermediate and high classes happen to be possible geothermal zones, and they occupy 49% of the study area (38,077 km2). The Riverline was superimposed on the LST, and the high-temperature sites were located by the identification tool. Streams/river data overlapped on the selected sites were regarded as thermal/warm springs. Remarkably, the LST results show lower temperatures (<36°C) at the famous thermal springs (Awe and Wukari) than some unknown rivers/streams found in Kwande (38°C), Ussa, (38°C), Gwer East (37°C), Yola Cross and Ogoja (36°C). Furthermore, the geophysical datasets, regional gravity, and high-resolution aeromagnetic data were interpolated to delineate the subsurface features associated with geothermal manifestations. The four layers from the LST were further evaluated using the geophysical approach. Gravity and magnetic values revealed variations that could be linked to geothermal alterations. The correlation of the geophysical anomalies and LST with the geology of the study area uncovers essential information on energy potentials. Therefore, further investigation is required to estimate the depth of the causative body, the geothermal gradients, and the reservoir volumes.

Imaging magmatic intrusions using derivatives of high-resolution aeromagnetic data over the Nigerian sector of the chad Basin

Magmatic activities can either positively or negatively affect hydrocarbon generation in sedimentary basins. The effect of these activities can be positive when they prevent further migration and escape or negative when extreme pressure and high temperature force the hydrocarbon to evaporate at the time of emplacement. The aim of the study is to confirm the presence of intrusive structures in the Nigerian sector of the Chad Basin using derivatives of aeromagnetic data. The enhanced body and edges suggest a dyke-like structure intruding the Chad Basin. The edges are identified as areas that are skewed on the first vertical derivative and maxima over the analytic signal generated by the dyke-like intrusion. Three profiles with lengths ranging from 68.4 km to 263.9 km were generated on the derivatives of aeromagnetic data, and the analytical results indicate dyke-like structures of 0.3 km to 0.4 km in size.

Aeromagnetic investigation of crustal stability of Osi, north central Nigeri

High-resolution aeromagnetic data of Osi north central Nigeria has been processed with a view to establish the earthquake-prone fault zones in the area. The analytical signal amplitude, shaded relief total horizontal derivative, first vertical derivative and 3D Euler deconvolution maps produced from the residual magnetic intensity anomalies of the study area identified the structural features in the area. The locations and the orientations of the extracted magnetic lineaments were revealed by the structural map of the area and the associated rose diagram. The lineaments were observed to strike NE-SW, ENE-WSW, E-W, NW-SE, WNW-ESE, NNE-SSW and NNW-SSE. The upward continuation maps showed evidence of deep-lying faults while the source parameter imaging and spectral analysis revealed depth to magnetic sources ranging from 81 m to 402 m and 103 m to 460 m respectively. The predominant NE-SW and NNE-SSW trending faults in the study area depicted stress history related to Ifewara faults; which is an indication of possible impending earthquake occurrence in the area.

3D modeling of the Esker intrusive complex, Ring of Fire intrusive suite, McFaulds Lake greenstone belt, Superior Province: Implications for mineral exploration

A 3D geological model of the Archean Esker ultramafic–mafic intrusive complex of the Ring of Fire intrusive suite of northwestern Ontario (Canada) is presented, providing insight into the nature of its magmatic plumbing system and allowing for speculation on the formation of its valuable Ni-Cu-(PGE) and chromitite deposits. The 3D model was constrained by exploration drillholes and high-resolution aeromagnetic data, which allowed the interpretation of the broad internal structure of the intrusive complex and two shear zones, which define for a major part of their strike extent the contacts between ultramafic and overlying mafic intrusive rocks. Restoring the post-emplacement component of strike-slip displacement and subsequently rotating the intrusive complex back from its tilted to sub-horizontal orientation of emplacement, provides a three-dimensional rendition of a 14 km-long dominantly tabular-shaped intrusive complex. The complex is defined by intact basal intrusive contacts with localized keel-shaped ultramafic promontories parallel to a nearby blade-shaped magmatic conduit. The keels extend in a subparallel orientation to depths of up to 1 km into the underlying tonalitic rocks and coincide with significant offsets of the basal intrusive contact, leading to speculation that their intrusion may have been guided by pre-existing normal faults. Two of these magmatic conduits host Ni-Cu-(PGE) deposits/prospects that formed from gravitational segregation of sulfides. The chromitite deposits, hosted in ultramafic rocks at higher stratigraphic levels, were modeled based on drill hole assay data. Zones of dominantly massive to semi-massive chromitite were defined by the ≥ 35% Cr2O3 threshold, while intercalated sequences of chromitite in dunite/peridotite were defined by the ≥ 15% to ≤ 35% Cr2O3 percentage range. The 3D modeled surfaces fitted to these constraints exhibit ore zones with lateral extents from several hundreds of meters for massive bodies up to a maximum of 2 km for intercalated chromitite ore that are dominantly conformable to the layering of the ultramafic host rocks. The lack of lateral continuity of chromitite ore zones beyond this scale, suggests that the chromitite layers are not continuous along the entire strike extent of the Esker intrusive complex, which is consistent with bifurcations of the 3D modeled ore shells signifying pinch-outs of both the massive chromitite layers and the dunitic interlayers. This discontinuous distribution of chromitite ore resembles that in the stratiform deposits of the Stillwater Complex and may support recent models of mechanical segregation of chromitite from cotectic chromite-olivine slurries. Based on our 3D model, we propose that the Esker intrusive complex evolved as a series of individual intrusions that were emplaced during multiple magmatic pulses that eventually coalesced to form a composite ultramafic–mafic complex prior to being dissected and partly dismembered by post-ore shear zone deformation.

Under-Displaced Normal Faults: Strain Accommodation Along an Early-Stage Rift-Bounding Fault in the Southern Malawi Rift

One of the fundamental problems in continental rift segmentation and propagation is how strain is accommodated along large rift-bounding faults (border faults) since the segmentation of propagating border faults control the expression of rift zones, syn-rift depo-centers, and long-term basin evolution. In the Southern Malawi Rift, where previous studies on the early-stage rifting only assessed border fault structure from surficial and topographic expression, we integrate surface and subsurface data to investigate border fault segmentation, linkage, and growth as proxies for strain accommodation along the Bilila-Mtakataka Fault (BMF) System. We used 30 m-resolution topographic relief maps, electrical resistivity tomography (ERT), and high-resolution aeromagnetic data to characterize the detailed fault geometry and provide a more robust estimate of along-fault displacement distribution. Our results reveal a discrepancy between sub-aerial segmentation of the BMF geometry (six segments), scarp height (five segments) reflecting the most recent episodes of fault offset, and cumulative throw (three composite segments) reflecting the long-term fault offset. We also observe that although the BMF exhibits continuity of sub-aerial scarps along its length, the throw distribution shows a higher estimate at the Northern-to-Central segment relay zone (423 m absolute, 364 m moving median) compared to the Central-to-Southern segment relay zone (371 m absolute, 297 m moving median). The ERT profiles across the relay zones suggest a shallower basement and a possible canyon-mouth alluvial fan stratigraphy at the Central-to-Southern segment relay zone, contrasting the deeper basement and “simpler” electrical stratigraphy at the Northern-to-Central relay. The results suggest a more complex long-term evolution of the BMF than was assumed in previous studies. A comparison of BMF’s maximum displacement-vs-length with those of other Malawi Rift border faults and global normal fault populations suggest that although the BMF has possibly reached its maximum length, it remains largely under-displaced as its 580–837 m maximum displacement is significantly lower than that of faults of equivalent length. We suggest that the BMF may continue to accrue significant strain as tectonic extension progresses in the Southern Malawi Rift, thus posing a major seismic hazard in the region.

INVESTIGATION OF GEOTHERMAL ENERGY RESOURCE POTENTIAL USING AERO-MAGNETIC AND AERO-RADIOMETRIC DATA OF KANO, NIGERIA

This study focused on investigating the geothermal resource potential in Kano using high resolution aeromagnetic and radiometric data. A total of sixteen (16) sheets of aeromagnetic data with a block dimension of 55 km x 55 km were processed. Thus, the spectral centroid method which result from low wave number part of the wave number-scaled (depth to the centroid) and high-wave-number portion of the power spectrum (depth to the top) were estimated. Thus, the Curie point depth (CPD), geothermal gradient and heat flow were determined using appropriate parameters. The results showed that the CPD values range from 4.27 km to 19.59 km with an average of 11.83 km, and geothermal gradient ranges from 29.6 oC/km to 135.7 oC/m with an average of 82.7 oC/km while the heat flow ranges from 74 mW/m2 to 339.2 mW/m2 with the average of 206.6 mW/m2. Areas with high heat flow and shallow CPD could be prospective areas for geothermal energy. The values of the radiogenic heat obtained in the study area range from 0.15 to 2.77 μW/m3. It was observed that the highest radiogenic heat generation in the area is greater than the average radiogenic heat values in the continental crust. The information obtained from temperature to depth model reveals that, the Curie temperature could be reached at the depths of 6 km within the regions.

Delineation of structural lineaments of Southeast Nigeria using high resolution aeromagnetic data

Abstract Structural lineaments of Southeast Nigeria were delineated using high-resolution aeromagnetic data. Advanced methods such as enhanced horizontal gradient amplitude (EHGA) involving a 3D model and tilt depth method (TDM) were used in this study. The simulated magnetic model involving the EHGA detector positioned peaks over source borders and created sharp and clear edges for magnetic sources. The TDM is a cutting-edge depth determination method revealing the depth of the contacts and thickness of sedimentary bodies that vary from ∼500 to ∼2,500 m and ∼3,000 to ∼5,000 m, respectively. Lineaments of the study area were extracted from the EHGA map. The structural map showed the dominance of short-ranged (∼0.29 to ∼1.48 km) linear magnetic anomalies. In addition, regional geologic structures (∼2.8 to ∼24.5 km) occur at the western flank of the study area. In general, these structures trend in the NE–SW, NNE–SSW, N–S, E–W, and NW–SE directions. They are indicators of subsurface faults, contacts, and tectonic structures of the thermo-tectonic events associated with Santonian Abakaliki Anticlinorium, Tertiary-Recent Ikom-Mamfe Rift, and structural deformations of the basement rocks associated with the Oban Massif.