Analysis Of Aeromagnetic Data Research Articles

Geothermal energy potential from analysis of aeromagnetic data of part of the Niger-delta basin, southern Nigeria

In the quest for alternative or renewable energy resource, attention is being focused on geothermal energy within some parts of the Niger Delta Basin of Nigeria with the aim of exploring/identifying its geothermal potentials. A MATLAB program was used to perform regional-residual separation and spectral analysis on composite-eight (8) aeromagnetic maps. Specifically, statistical spectral analysis was used to determine Curie point depth and heat flow values within this area. Results showed that the centroid depth varies between 14.4194 km (within Okigwe – Aba sector) and the 6.7482 km (within Aba-Ahoada region) while the depth to Curie temperature isotherm varies between 7.4644 km and 24.8600 km below the mean sea level. It was also found that the Curie temperature isotherm within the basin is not a horizontal level surface but an undulating surface with geothermal gradients and heat flow ranging between 12.0676 and 40.1910 °C/Km and 25.3419 and 84.4010 mW/m2 respectively. Thus the calculated average geothermal gradient and heat flow for this area are 22.4886 °C/Km and 52.6012 mW/m2 respectively. Since the value obtained from this work is below 100 mW/m2 which is the minimum standard, it then means that this area may not potential be viable as a geothermal source.

English

Twelve sheets of aeromagnetic and aeroradiometric data covered the study area. The data was used to investigate heat sources. The aeromagnetic data were combined to form a composite map- total magnetic intensity (TMI) anomaly map and aeroradiometric data of each radio-element were combined to produce the radioelements maps. Regional-residual separation of the total magnetic intensity data was performed using polynomial fitting method on the aeromagnetic data. The filtered residual data was Fourier transformed after dividing the whole area into thirty-five overlapping sections for spectral analysis, to determine Curie point depth, geothermal heat flow and magnetic trends. Calculation of ratios was used for the radio-elements to estimate the radioactive heat values in the study area, and the surface geology of the study area was delineated to outline each rock unit to match their density and corresponding radio-elements. The results of the analysis of aeromagnetic data showed that the shallow magnetic source ranges from 0.59 to 3.86 km, deeper source ranges from 8.03 to 19.85 km, Curie point depth values ranges from 14.64 to 38.62 km and geothermal heat flow values ranges between 37.54 and 99.02 mWm-2. The results of the analysis of the radioactive heat production of the study area range between 0.01 and 5.43 μWm-3. The highest heat produced was from the Shale with radioactive heat production as high as 5.43 μWm-3. There are high geothermal heat flow and radioactive heat values in Aimeke and Ogobia.   Key words: Aeromagnetic, aero-radiometric, radioactive, geothermal.

Curie depth and geothermal gradient from spectral analysis of aeromagnetic data over Upper Anambra and Lower Benue Basin, Nigeria.

The resent (2009) aeromagnetic data covering lower part of Benue and upper part of Anambra basins was subjected to one dimensional spectral analysis with the aim of estimating the curie depth and subsequently evaluating both the geothermal gradient and heat flow for the area. Curie point depth estimate obtained were in the range of 25 km to a maximum of 32 km, the maximum values where obtained within the regions of positive magnetic anomalies. The geothermal gradient within this area varies between 320C/km to 800C/km. The highest geothermal gradient is observed around Katakwa at the northern edge, which host the young granitic rocks of central Nigeria and around Lokoja which host undifferentiated old granites of western Nigeria. Heat flow values obtained are between 46mW/m2 and 98 mW/m2. Shallow Curie point depths, high geothermal gradient and high heat flow, located at two geometric basement highs at the western and northern parts, correlate with regions with high concentration of both potassium and Thorium concentrations as observed on the ternary map.Keywords:- Geothermal Gradient, International Geomagnetic Reference Field (IGRF), Benue Trough

Aeromagnetic signature analysis of Gasus area and its surrounding, central eastern desert, Egypt

This study presents analysis and interpretation of aeromagnetic data to construct subsurface structure maps and determine the depths to magnetic basement. Subsequent analysis steps are applied to the total magnetic intensity (TMI) data. These steps include Reduction to the Pole (RTP) map that was derived from the TMI map then subjected to spectral frequency analysis to isolate RTP map into high and low frequencies and determine pseudo-depth for each map from power spectrum in which there were two main average levels (interfaces) at depth 1.3 and 0.7 km for the deep-seated and near-surface magnetic structures, respectively. 3D Euler deconvolution technique is applied to calculate the depth to the magnetic contacts; the results show clustering of solutions, the shallow solutions are related to the outcrops less than 80 m from flight level, and the solutions which are related to sedimentary cover locations (Um al-Huweitat, Wasif, and Mohamed Rabah basins) are ranged between 200 and to more than 1100 m. Moreover, anomaly enhancement techniques such as tilt derivative (TD), horizontal tilt derivative (TDX), and source edge detect (SED) are applied to enhance shallow features, and determining structure element boundary for both shallow- and deep-seated anomalies and revealing possible faults such as 2D forward modeling are applied to selected profiles to adjust the interpreted structures and map the boundaries and basement relief of the three basins (Mohammed Rabah, Wasif, and Um al-Huweitat). The analysis shows that the study area is affected with network of dip–slip faults due to high shearing and compression stress which formed grabens and horsts at different depth levels in the study area. The trends of predominant faults related to deep-seated structures are NW–SE with depths ranged between 1 and 1.4 km and in regard to the shallow-seated structure, the predominant fault trends are NW–SE, NNW–SSE, and NNE–SSW with depths ranged between 0.3 and 0.8 km.

Mapping of Lineament Structures using Potential Fields Data in Lafiagi Area, Central Nigeria

An evaluation of the lineament features over a part of the transition environment between the Basement complex rocks of the southwestern Nigeria and the Sedimentary rocks of the Nupe Basin was carried out. It was aimed at identification of the structural features responsible for the tectonics and hydrogeology of the area. The work involved the qualitative and quantitative analysis of aeromagnetic data and pseudogravity transforms using Oasis MontajTM. The 3-D Euler Deconvolution results from acquired potential fields data, augmented with geologic information were employed in the lineaments extraction and interpretation work. The results have shown that the mapped lineament features generally coincide with the river channels on the geologic and drainage maps which indicate a structural control of the drainage system in the study area. The rose diagram of the extracted Euler solutions’-based lineament features and that of the local geology showed a predominance of NE-SW and N-S trends respectively, typical of the post-Pan African lineaments.

Depth of magnetic basement in Iran based on fractal spectral analysis of aeromagnetic data

Depth of magnetic basement in Iran based on fractal spectral analysis of aeromagnetic data

Estimation of Sedimentary Thickness Using Spectral Analysis of Aeromagnetic Data over Part of Bornu Basin, Northeast, Nigeria

Estimation of Sedimentary Thickness Using Spectral Analysis of Aeromagnetic Data over Part of Bornu Basin, Northeast, Nigeria

Evidence of Structural Facts Inferred from Aeromagnetic Data Analysis over the Guider-Maroua Area (Northern Cameroon)

In this study, we performed some filters to highlight geological structures and/or features which are found in the igneous rocks, between the latitudes 9°45'N to 10°45'N and longitudes 13°15'E to 14°30'E. The application of the first vertical derivative (FVD) and the horizontal gradient magnitude (HGM) on a total magnetic data over the study area has led to put in evidence: 1) geological features as geological boundaries, faults, dykes, folds on the FVD map; 2) abundant aeromagnetic lineaments probably fractures, dykes and contacts, ex-hibit a conjugate relationship suggesting a near NE and NW tectonic trends; 3) existence of a possible prominent near E-W compression, characterized by a possible dextral displacement of geological formations by the shear movements; 4) and the magnetic signature of the country rocks.

Application of 3D Euler deconvolution of aeromagnetic data and pseudogravity transforms in mineral exploration: a case study of the pegmatite-rich zones of Lafiagi, Central Nigeria

Structural evaluation of the pegmatite-rich zones in a part of Lafiagi (Sheet 203), Central Nigeria, was carried out. It was aimed at identification of the structures responsible for the rich mineralization of the area. This work involved the qualitative and quantitative analysis of aeromagnetic data and pseudogravity transforms by using Oasis Montaj™ software. The 3D Euler deconvolution results from acquired aeromagnetic data and pseudogravity transforms augmented with geological information obtained from reliable sources were employed in the structural interpretation work. The results have shown that the abundance of 2D and 3D structures that are commonly associated with gemstones and precious minerals explain why the study area is rich in mineral deposits.

Structural analysis of aeromagnetic data from the Rainy River Block, Wabigoon subprovince, Minnesota, USA and Ontario, Canada: Strain partitioning along a Neoarchean terrane boundary and implications for mineral exploration

High-resolution aeromagnetic data are used to constrain the structural architecture and mineral potential of the Neoarchean Rainy River Block (RRB)—a sigma-shaped wedge of till-covered volcano-plutonic rocks that form the southern margin the Wabigoon subprovince and span the international border between northern Minnesota, USA and western Ontario, Canada. Reduced-to-pole transformed, upward continued and derivative enhanced aeromagnetic data show that the RRB can be divided into three structural domains: the Rainy Lake wrench zone (RLWZ), Border zone (BZ), and Oaks belt (OB). Strain intensity decreased from east (strongly deformed RLWZ) to west (moderately deformed OB). The RLWZ experienced superimposed folding that resulted in complex rock geometries and sigmoidal patterns in the aeromagnetic data. A large northeast trending syncline, partially represented by an aeromagnetic low that is cut by similarly oriented shear zones and faults, comprises the BZ. The OB is interpreted to occupy a regional-scale strain shadow and is composed of a relatively well preserved and magnetically heterogeneous volcanic pile and subvolcanic intrusion that have been overturned and are steeply north dipping. As the RRB is fault-bounded terrane boundary and hosts numerous mafic intrusions, it was a regional zone of synvolcanic and syntectonic paleo-permeability and, therefore, has potential for hosting orogenic gold and volcanogenic massive sulfide (VMS) deposits. However, linear fault geometries throughout most of the RRB were not conducive to formation of large orogenic gold deposits and pervasive deformation in the RLWZ may have compromised preservation of hypogene VMS mineralized zones. Thus, the structurally preserved OB is the most prospective area for hosting VMS deposits in the RRB, whereas the BZ and surrounding rocks are prospective for hosting orogenic gold deposits near a ∼30km long restraining bend in the Quetico Fault.

Curie point depth and heat flow from spectral analysis of aeromagnetic data over the northern part of Western Desert, Egypt

The present work aims to estimate the Curie point depth and the surface heat flow for the northern part of the Western Desert using aeromagnetic data. Applying spectral analysis to aeromagnetic anomalies has provided equitable promising geological results, useful for further geothermal or petroleum exploration. The total intensity aeromagnetic map was first reduced to the north magnetic pole to correct the shape and position of different magnetic anomalies over their causative bodies. Secondly, the short wavelengths were removed to enhance the deeper long wavelengths related to the deep sources. Spectral analysis indicates that the area is underlined by an average Curie point depth of about 27km. This implies an average thermal heat flow (53mW/m2) lower than the average global heat flow. The investigated area was divided into eighteen blocks, where the average depths to centroid and top of the magnetic source were estimated for each block. The results of this work show a general depth increase of the magnetic boundaries from 24.5km in the southern area to 33km at the northern part. The calculated surface heat flow decreases from about 56 to 42mW/m2 in the same direction. Consequently, this area is characterized by its low geothermal gradient and surface heat flow. This low geothermal gradient indicates that the upper mantle contributes to the magnetic features at the northern offshore parts. This work also recommends by deep drilling for petroleum exploration and production within the Egyptian Mediterranean Sea exploration strip.

Exploration for limestone deposit at Onigbedu, South–Western Nigeria

Abstract The Onigbedu limestone deposit was investigated using the aeromagnetic data, resistivity soundings and borings with the aim of characterizing the limestone deposit and estimating its reserves. The subsurface structural features and depth to basement were identified with the analysis of aeromagnetic data. Twenty nine boreholes were drilled for subsurface appraisal and correlation of the limestone deposit. Eighty nine Vertical Electrical Sounding (VES) were acquired using the Schlumberger array. The results showed NE-SW trending lineaments that segmented the limestone. Depth to basement varied from 144.2 m to 1090 m. The VES results showed four to six layers indicating the topsoil (7-315 Ωm), clay (2-25 Ωm), shale (6-31 Ωm), limestone (20-223 Ωm), sandstone (>200 Ωm) and sandy materials. The VES results correlated well with the lithological unit delineated from the borehole. The overburden thickness ranged from 3.3 m to 28 m, while the limestone thickness varies between 18.1 m and 48.3 m. The limestone reserve was estimated at 1.9 × 109 t. This study concluded that the study area had vast occurrence of the limestone deposits, which would be of economic importance, if exploited.

New insights from geophysical data on the regional structure and geometry of the southwest Thelon Basin and its basement, Northwest Territories, Canada

Detailed analysis of gravity and aeromagnetic data covering the southwest Thelon Basin, Northwest Territories, Canada, has provided insight into basement geology that has significance to exploration for uranium and possibly other economic metals in a remote frontier region. Interpretation of basement geology has been constrained by the calibration of gravity and magnetic signatures with Precambrian geology adjacent to the basin and sparse seismic data within the basin, creating the first basement geologic map of the southwest Thelon Basin. The basement to the overlying sedimentary units is dominated by magnetic felsic and mafic bodies variably overlying and intruding the gneissic crystalline basement. Supracrustal belts located outside the basin margins are interpreted to continue below the basin fill. Major structures have been delineated geophysically including the Howard Lake Shear Zone and the Bathurst and McDonald fault systems. Northwest-trending structures forming part of the Bathurst fault system appear to control the unconformity surface morphology and the location of basin depocenters. The geologic interpretations are corroborated by joint gravity and magnetic modeling of profiles that reveal the deepest part of the Thelon Basin reaches depths of [Formula: see text] in an area of subdued magnetic and gravimetric response to the north. The basin is a focus of active exploration for uranium, and we have found that areas along the south and eastern margins underlain by U-rich granitoid rocks may have significant potential where intersected by reactivated faults.

The deep crust beneath the Trans‐European Suture Zone from a multiscale magnetic model

AbstractWe present a 3‐D interpretation of the deep magnetic sources beneath the main geological structure of central‐eastern Europe, the “Trans‐European Suture Zone” (TESZ). We used a multiscale analysis of aeromagnetic data, based on a multiscale data set generated by upward continuation of the European and Mediterranean Magnetic Project data set from 5 to 100 km altitude. We also computed the multiscale total gradient |∇T| of the multiscale field. Both of the multiscale data sets allow us to discriminate the main crustal contributions to the field at various scales, and we showed that at large altitudes the field is dominated by the sole effect of the TESZ. The multiridge geometric method was very useful in studying the complex features of the main crustal interfaces, either shallow or deep. The interpreted interfaces are largely agreement with geological models based on seismic surveys and, in some cases, complete the models out of the analyzed region. In order to estimate the deepest source depths in the TESZ region, we applied the multiridge method to the large scales (50–100 km altitude), obtaining a set of singular points at depths ranging between 35 and 40 km. Considering the heat flow trend and the geological models around the TESZ area, we found a meaningful correspondence among the location of the estimated singular points and the most abrupt variations and complex morphology features of the Moho boundary. The multiridge estimates are consistent with known structural information and can be used for a 3‐D representation of the Moho depth along the TESZ.

Inferring the subsurface basement depth and the structural trends as deduced from aeromagnetic data at West Beni Suef area, Western Desert, Egypt

The present work aimed to delineate the subsurface structures and to estimate the magnetic source depth at the selected area lying in West Beni Suef area, Western Desert, Egypt, following different geomagnetic techniques. The analysis of aeromagnetic data demonstrates five significant tectonic faults trending to NW-SE, ENE-WSW, NE-SW, E-W and NNW-SSE directions constructed using Euler deconvolution techniques. The execution of this study is initiated by transformation of the total intensity aeromagnetic data to the reduced to pole (RTP) magnetic intensity. This is followed by applying several transformation techniques and various filtering processes through qualitative and quantitative analyses on magnetic data. The reduced to the northern magnetic pole (RTP) data are separated spectrally into regional and residual magnetic components using the computed power spectrum of the magnetic data. The estimated mean depths of both regional and residual sources are found to be 5.27km and 2.78km respectively. Also, depth estimations have been conducted by application of the Euler deconvolution and 2-D modeling techniques. The results indicate that the eastern and northern parts of the study area discriminate deeper basement relief and the depth of basement surface reaches to 5095m. While the southern and western parts of the study area discriminate shallower basement relief and the depth of basement surface reaches to 227m. This study has given a clear picture of the geologic structures beneath the study area.

Determination of Depth to Magnetic Sources Using Spectral Analysis of High Resolution Aeromagnetic Data over IBBI and Environs, Middle Benue Trough, North Central Nigeria

Determination of Depth to Magnetic Sources Using Spectral Analysis of High Resolution Aeromagnetic Data over IBBI and Environs, Middle Benue Trough, North Central Nigeria

Internal architecture of the Tuxtla volcanic field, Veracruz, Mexico, inferred from gravity and magnetic data

The Tuxtla Volcanic Field (TVF) is a basaltic volcanic field emerging from the plains of the western margin of the Gulf of Mexico in the Mexican State of Veracruz. Separated by hundreds of kilometers from the Trans-Mexican Volcanic Belt to the NW and the Chiapanecan Volcanic Arc to the SE, it stands detached not only in location but also in the composition of its rocks, which are predominantly alkaline. These characteristics make its origin somewhat puzzling. Furthermore, one of the large volcanoes of the field, San Martin Tuxtla, underwent an eruptive period in historical times (CE 1793). Such volcanic activity conveys particular importance to the study of the TVF from the perspective of volcanology and hazard assessment. Despite the above circumstances, few investigations about its internal structure have been reported. In this work, we present analyses of gravity and aeromagnetic data obtained from different sources. We present the complete Bouguer anomaly of the area and its separation into regional and residual components. The aeromagnetic data were processed to yield the reduction to the pole, the analytic signal, and the upward continuation to complete the interpretation of the gravity analyses. Three-dimensional density models of the regional and residual anomalies were obtained by inversion of the gravity signal adding the response of rectangular prisms at the nodes of a regular grid. We obtained a body with a somewhat flattened top at 16km below sea level from the inversion of the regional. Three separate slender bodies with tops 6km deep were obtained from the inversion of the residual. The gravity and magnetic anomalies, as well as the inferred source bodies that produce those geophysical anomalies, lie between the Sontecomapan and Catemaco faults, which are proposed as flower structures associated with an inferred deep-seated fault termed the Veracruz Fault. These fault systems along with magma intrusion at the lower crust are necessary features to understand the origin and structure of the TVF.

Arcabouço geofísico-estrutural da porção meridional do Cinturão Ribeira

Os diversos estudos apresentados para explicar a configuração atual e a evolução da porção meridional do Cinturão Ribeira refletem a complexidade dos processos envolvidos na formação desses terrenos. Com base na análise qualitativa (realce de anomalias) e semiquantitativa (estimativas de profundidades de fontes) de dados aeromagnéticos e modelagem gravimétrica, o presente trabalho apresenta modelos geofísico-geológico-estruturais dessa região. A integração de resultados qualitativos e semiquantitativos, balizada pela geologia da área, constituiu a base para elaboração dos modelos. A aplicação de métodos de realce de anomalias (análise qualitativa) mostrou a continuidade de lineamentos correspondentes à Zona de Falha de Taxaquara e às zonas de cisalhamento Itapirapuã, Morro Agudo e Lancinha sob a Bacia do Paraná. Tal interpretação foi validada pelas soluções de Euler, que mostram profundidades superiores a 2.000 m, relacionadas a essas estruturas, tanto no embasamento como em seus prolongamentos sob a Bacia do Paraná. Os modelos gravimétricos, elaborados em níveis de profundidade distintos, indicaram um afinamento crustal de NW para SE, com porções de espessura crustal diferenciadas limitadas pelas zonas de cisalhamento.

Insights into the continental structure of southeast Australia and Tasmania from passive seismic and magnetic datasets

SUMMARY The continental crust of southeast Australia is a complex and highly prospective area. Southeast Australia comprises the Delamerian and Lachlan Orogenies which, together with the Eastern Tasmania Terrane, are understood to have Phanerozoic basement. In contrast, the Western Tasmanian Terrane comprises areas of exposed Neoproterozoic basement which were assembled along the proto-Pacific margin of East Gondwana. In this study, the crustal structure across southeast Australia and Tasmania is considered using seismic and aeromagnetic methods. We use previous passive seismic results and present a new analysis of magnetic data. The Curie temperature, the temperature at which magnetic rocks lose their magnetisation, is investigated using spectral analysis of aeromagnetic data and the Curie point depth (CPD) is consequently determined. CPD is compared to the depth of the seismic Moho discontinuity throughout the study area. The Moho depth and newly calculated CPD throughout the study area vary from ~20 to >38 km and ~25 to >45 km, respectively. The CPD is slightly shallower than the Moho across the study area. The Delamerian and Lachlan Orogenies are underlain by a 30-35 km and ~4050 km deep Moho respectively, while average CPD depths are ~30 and ~28 km for these regions. A relatively shallow CPD is observed in the northeast of the study area and corresponds to Cainozoic volcanism in eastern Australia. The shallow Moho beneath Tasmania supports the idea of crustal thinning during Gondwana breakup. In Tasmania, CPD increases in depth from ~21 km in the northwest to >31 km in north. This is consistent with variations in the depth of the Moho from 25 km in the northwest to 37 km in the north.

Curie point depth from spectral analysis of aeromagnetic data for geothermal reconnaissance in Afghanistan

The geologic setting of Afghanistan has the potential to contain significant mineral, petroleum and geothermal resources. However, much of the country's potential remains unknown due to limited exploration surveys. Here, we present countrywide aeromagnetic data to estimate the Curie point depth (CPD) and to evaluate the geothermal exploration potential.CPD is an isothermal surface at which magnetic minerals lose their magnetization and as such outlines an isotherm of about 580 °C. We use spectral analysis on the aeromagnetic data to estimate the CPD spatial distribution and compare our findings with known geothermal fields in the western part of Afghanistan.The results outline four regions with geothermal potential: 1) regions of shallow Curie point depths (∼16–21 km) are located in the Helmand basin. 2) regions of intermediate depths (∼21–27 km) are located in the southern Helmand basin and the Baluchistan area. 3) Regions of great depths (∼25–35 km) are located in the Farad block. 4) Regions of greatest depths (∼35–40 km) are located in the western part of the northern Afghanistan platform. The deduced thermal structure in western Afghanistan relates to the collision of the Eurasian and Indian plates, while the shallow CPDs are related to crustal thinning. This study also shows that the geothermal systems are associated with complex magmatic and tectonic association of major intrusions and fault systems. Our results imply geothermal gradients ranging from 14 °C/km to 36 °C/km and heat-flow values ranging from 36 to 90 mW/m2 for the study area.