ABSTRACT
Aeromagnetic data over some part of the Chad Basin, Nigeria was analyzed. The aeromagnetic anomaly map, its qualitative and quantitative interpretation helped in identifying the nature and depth of the magnetic sources in the study region. The regional-residual separation was performed with a first order polynomial using oasis montaj software. The residual data obtained was contoured into 3-D maps and this revealed two prominent magnetic anomaly source intensities; the low frequency anomaly and the high frequency anomaly sources. The low frequency anomalies emanates from deep seated bodies in areas with thicker sediments and may be viewed as the magnetic basement depth. The high frequency anomaly emanates from shallow seated geologic bodies in areas of shallower sediments and may be attributed to the volcanic rocks that intruded into the sedimentary formation and this could possibly be responsible for the mineralization found in the area. The maximum magnetic field amplitude is greater than 223 nT mostly above the earth surface while the lowest is less than 96 nT. Varying magnetic highs and lows have been found in the study area which might likely indicate undulating basement surface and likely traps. Depth to the basement of the basin structure ranges from about 0.5 km in the southern part of the study area and gets deeper toward the northern part up to 3.0 km. Lineament and structural complexity map and magnetic depth map values have been utilized to construct the interpretation of the main subsurface structures affecting the studied area, which correlate with the previous studies of the Chad Basin. The lineaments map shows the long regional trends which control the subsurface structure beneath the studied area in an ENE–WSW, WNW–ESE and E–W dominant structural trends directions. Results of the Spectral analysis method enabled delineation of the lithology and mapping the depths of subsurface geologic structures. The study indicated that there is a major source of disturbance at the southern end of the map which trends in an approximately NE-SW direction and is a possible target for feature analysis as it has very high magnetic field anomaly.
Also, the Standard Euler 3D plots in clear terms showed that the shallow depth of about 214 m for the possible causative sources. The depths in the eastern part of the area are not uniform. In the study area, maximum depth is greater than 770m and is found mostly at the southwestern part of the area where the highest magnetic field intensity amplitude from TMI is located. Therefore, this area has the thickest sedimentary rocks and could be the most probable areas for future analysis. The Energy Power Spectrum calculated average depth to the top of regional sources is about 7 km whereas the shallow sources have depth of about 1.5 km as an average depth to their sources. The depth to the top of the intrusive causative targets was calculated from the aeromagnetic map using spectral analysis method. It was found that the depth result generally ranges from 285.6 m (outcropping and shallow magnetic bodies) to 5400.3 m (deep lying magnetic bodies).
Title page
i[D1]
Declaration
ii
Certification
iii
Dedication
iv
Acknowledgement
v
Abstract
vii
Content
viii-x
List of Figures
xi
List of Tables
xii
List of abbreviations and symbols
xiv-xv
CHAPTER ONE: INTRODUCTION
1.1 Background to Study
1-6
1.2 Statement of Problem
7
1.3 Aim and Objectives
7
1.3 Aim and Objectives
7
1.4 The Geography of the Area
8-11
1.4.1 Topography
8
1.4.2 Drainage
9
1.4.3 Climate
9-10
1.4.4 Vegetation
10-12
1.4.5 People
12-13
1.4.6 Economy
13-15
CHAPTER TWO: LITERATURE REVIEW
2.0 Literature Review
15
2.1 Previous work done
15-19
2.2 Geology of the area
19-23
2.2.1 The Chad Formation
23-27
2.3 Basic theory of aeromagnetic method
29-33
CHAPTER THREE: MATERIALS AND METHODOLOGY OF STUDY
3.1 Data Acquisition
34-36
3.2 Data Interpretation
37
3.2.1 Regional- Residual separation using the Fast Fourier Transform (FFT)
38
3.2.2 Reduction-to-the-pole
38
3.2.3 Edge detection methods (Source Edge Detection)
39
3.2.3.1 The tilt angle derivative (TDR)
39
3.2.3.2 Standard 3D-Euler Deconvolution (ED)
39-41
3.2.4 Depth to basement estimation
41
3.2.4.1 Analytic signal (total gradient) method
41-42
3.2.4.3 Source Parameter Imaging (SPI) Technique (local wave number technique)
42-43
CHAPTER FOUR: RESULTS AND DISCUSSION
4.0 Introduction
45
4.1 Results
45
4.2.1 Total Magnetic Intensity Data
45-46
4.2.2 Lineament Extraction and Presentation
47-49
4.2.3 Edge detection for depth map presentation
50
4.2.3.1 The tilt angle derivative (TDR)
50-51
4.2.3.2 Standard 3D-Euler Deconvolution (ED)
52-53
4.2.4 Depth to basement estimation (Analytic signal (total gradient))
54-55
4.2.5 Energy Power Spectrum
56-57
4.2.6 Source Parameter Imaging (SPI)
57-62
CHAPTER FIVE: DATA ANALYSIS
5.1 Introduction
63
5.2 Data Analysis
63
5.2.1 Analyses of results of Total Magnetic Intensity
63-64
5.2.2 Analyses of results from Lineament
64-65
5.2.3 Analyses of edge detection results
65
5.2.3.1 The tilt angle derivative (TDR)
65
5.2.3.2 Standard 3D-Euler Deconvolution (ED)
65-66
5.2.4 Analyses of depth to basement estimation results
66
5.2.4.1 Analytic signal (total gradient)
66
5.2.4.2 Energy Power Spectrum
67
5.2.4.3 Source Parameter Imaging
67-68
CHAPTER SIX: CONCLUSION AND RECOMMENDATION
6.1 Summary
69
6.2 Conclusion
70-71
6.3 Recommendation
6.4 Appendix
71
72-79
Reference
80-84
LIST OF FIGURES
Figure 1: Map of Nigeria showing Bornu-Chad basin (After Obaje et al., 2004)
6
Figure 2: Map of the study area showing the various LGA’s within
17
Figure 3: Geologic Map of the Chad basin (modified after NGSA). Source: NGSA (2006). Geological and Mineral Resources Map, Nigerian Geological Survey Agency
27
Figure 4.1: Total Magnetic Intensity Colour-shaded Grid
46
Figure 4.2: Lineament map of the basin
48
Figure. 4.3: Rose plot diagram showing major structural trend
48
Figure 4.4: Structural complexity map of the study area
49
Figure 4.5: Tilt derivatives map of the study area
51
Figure 4.6: Standard 3D-Euler deconvolution of the study area
53
Figure 4.7: Analytical signal colour shaded relief map of the area
55
Figure 4.8: Power spectrum of aeromagnetic data showing the corresponding average depths
57
Figure4.9: Source Parameter Imaging of the study area
58
Figure 4.9a: Five Profiles across source parameter imaging of the study area
59
Figure 4.9b: Depth Presentation of profile 1
60
Figure4.9c: Depth Presentation of profile 2
60
Figure 4.9d: Depth Presentation of profile 3
61
Figure 4.9e: Depth Presentation of profile 4
61
Figure 4.9f: Depth Presentation of profile 5
62
LIST OF TABLES
Table 1: Generalized stratigraphic column of the study area (modified after Avbovbo et. al)
21
Table 4.1a: Lineament Orientation Data
72-75
Table 4.1b: Lineament Orientation
76-79
LIST OF ABBREVIATIONS AND SYMBOLS
Tm microtesla
nT nanotelsa
The gradient operator
Degree
m Minute
s Seconds
2D Two-Dimensions
3D Three-Dimensions
E East
e.g. Example
eq. Equation
et al. and others
Fig. Figure
GPS Global Positioning System
km kilometre
m metre
Ma Million years
N North
N – S North-South
NE – SW Northeast-Southwest
NNE North Northeast
NNPC Nigerian National Petroleum Commission
NNW –SSE North Northwest-South Southeast
NW – SE Northwest-Southeast
NYG Nigerian Younger Granite
SSW South Southwest
WSW West South West
Christopher, E. (2019). MAPPING OF MAGNETIC ANOMALIES IN SOME PARTS OF NIGERIA CHAD BASIN, USING AEROMAGNETIC DATA. Afribary. Retrieved from https://track.afribary.com/works/msc-project-final-combined-edited-final
Christopher, Emmanuel "MAPPING OF MAGNETIC ANOMALIES IN SOME PARTS OF NIGERIA CHAD BASIN, USING AEROMAGNETIC DATA" Afribary. Afribary, 06 Mar. 2019, https://track.afribary.com/works/msc-project-final-combined-edited-final. Accessed 24 Dec. 2024.
Christopher, Emmanuel . "MAPPING OF MAGNETIC ANOMALIES IN SOME PARTS OF NIGERIA CHAD BASIN, USING AEROMAGNETIC DATA". Afribary, Afribary, 06 Mar. 2019. Web. 24 Dec. 2024. < https://track.afribary.com/works/msc-project-final-combined-edited-final >.
Christopher, Emmanuel . "MAPPING OF MAGNETIC ANOMALIES IN SOME PARTS OF NIGERIA CHAD BASIN, USING AEROMAGNETIC DATA" Afribary (2019). Accessed December 24, 2024. https://track.afribary.com/works/msc-project-final-combined-edited-final