The succession of tectonic phenomena in the South-West Cameroon area suggests that structures from the upper mantle infiltrated and took advantage of the cracks and fractures left by these phenomena to get closer to t...The succession of tectonic phenomena in the South-West Cameroon area suggests that structures from the upper mantle infiltrated and took advantage of the cracks and fractures left by these phenomena to get closer to the earth’s surface. However, the intrusive structures closest to the surface remain poorly known. The objective of this work is to improve the knowledge related to the interpretation of gravity data in order to characterise the near-surface intrusive bodies in the South-West Cameroon area, and then analyse their mining and geothermal implications. To achieve this objective, the indirect, inverse and normalized standard deviation (NSTD) methods were used. The NSTD method was used to detect the contours of the intrusive bodies. The indirect method (spectral analysis) was used to determine the depths of the interfaces of three intrusive bodies, one located on the Bipindi-Ebolowa I axis (G5), the other on the Eseka-Pouma axis (G8) and the last on the Bokito-Monatele axis (G11). The results obtained show roofs located between 0 and 0.61 km, between 0 and 0.37 km and between 0 and 0.73 km for the G5, G8 and G11 bodies, respectively. Finally, the application of the 2D inversion method allowed us to estimate the density contrasts of the intrusive bodies (G5, G8 and G11). The superposition of the intrusive bodies detected by the NSTD with the geological and mineral resources map, as well as an analysis of the results obtained, gave indications of interesting zones for mining prospecting and for the search for geothermal reservoirs.展开更多
The tectonic study based on geophysical data has been carried out in Sub-Himalayas in Azad Jammu and Kashmir and northern Pakistan. A series of thin skinned and thick skinned faults have been delineated in the investi...The tectonic study based on geophysical data has been carried out in Sub-Himalayas in Azad Jammu and Kashmir and northern Pakistan. A series of thin skinned and thick skinned faults have been delineated in the investigated area on the basis of present study. In the study area compressional stresses caused by the collisional of Indian and Eurasian plates developed the northwestsoutheast trending faults which are Shaheed Gala thrust, Bagh basement fault, Kashmir boundary thrust and Kawai fault or Indus Kohistan seismic zone. The crustal thickness increases towards north due to the stacking of the thrust sheets along these faults. The Murree Formation thrusts over the Si- waliks molasse along the Shaheed Gala thrust. This fault dips at an angle of 43° northeast and joins the thick skinned Bagh basement fault in subsurface which are penetrated up to Moho depth. In the northeast of Bagh basement fault the northwest-southeast trending Kashmir boundary thrust has been delineated in the sedimentary-metasedimentary wedge which joins the Indus Kohistan seismic zone in the subsurface. The present study suggested that the Kawai fault which is running within Murree Formation cuts 16 km thick sedimentary-metasedimentary wedge and also joins the Indus Kohistan seismic zone in the subsurface.展开更多
An academic geophysical research as a regional gravity survey was made during1994 in the Western White Nile to infer the shallow crustal structures in the area. The result ofthe survey was compiled as a Bouguer anomal...An academic geophysical research as a regional gravity survey was made during1994 in the Western White Nile to infer the shallow crustal structures in the area. The result ofthe survey was compiled as a Bouguer anomaly map with a contour interval of 2 X 10^(-5)m/s^2. It isfound that the negative residual anomalies are related to the Upper Cretaceous sediments (NubianSandstone Formation) filling all depressions in the Basement complex surface while the positiveresidual anomalies are attributed to the relatively shallow or outcropping Basement rocks and thesteep gravity gradients are resulting from the sharp contacts between the sedimentary infill and theBasement rocks. To define the geological structures in the area, 9 profiles were studied. For eachof the profiles, measured and computed Bouguer gravity anomalies, crustal density model, subsurfacegeology evaluation were performed. A G-model computer program was applied in the gravity modeling,which is based on the line-integral method of gravity computation. A geological/structural map wasproposed showing inferred sedimentary basins, faulting troughs and uplifted Basement block andtectonic trends. The basins are believed to be fault-controlled which developed by extensionaltectonics (pull-apart mechanism). As for the mechanism and cause of faulting, the area is consideredas a part of the Central Sudan rift system which had been subjected to several tectonic eventssince Early Cambrian to Tertiary times which resulted in the formation of several fracture systemsassociated with block subsidence, rifting and basin formation.展开更多
In order to analyze and determine the geological structures of the Adamawa plateau, the terrestrial gravity data were combined to data computed from GGM02C gravity model. The dense gravity net obtained were further in...In order to analyze and determine the geological structures of the Adamawa plateau, the terrestrial gravity data were combined to data computed from GGM02C gravity model. The dense gravity net obtained were further introduced into qualitative and quantitative interpretations. The resulting Bouguer anomaly map obtained from combined data shows NE-SW direction which nearly coincides with the main direction of the fractures affecting the basement in the region and indicates strong gradients marking the presence of discontinuities between heavy and negative gravity anomaly. In order to conduct the quantitative interpretation of the combined gravity data, three profiles were drawn on the residual Bouguer anomaly map and therefore were interpreted using spectral analysis method and 3D density inversion. The knowledge of the depth and density of the geological structures show an uplift of dense rocks under the granite-gneiss substratum. This dense material found in the ENE-WSW direction of the Adamawa Plateau is interpreted as basaltic intrusion probably resulting from tectonic processes. According to this study, the depths of 3.83 km and 9.62 km are the new values of depths obtained for futures investigations in the Adamawa plateau.展开更多
The study area is located in the south western Cameroon and includes part of the Cameroon Volcanic Line (CVL). Volcanic activity has been recorded in this area, precisely on the Mount Cameroon which recently erupted i...The study area is located in the south western Cameroon and includes part of the Cameroon Volcanic Line (CVL). Volcanic activity has been recorded in this area, precisely on the Mount Cameroon which recently erupted in 2002. In addition, deadly carbonic gas was emitted by crater lakes (Monoun and Nyos) in 1984 and 1986 respectively. Potential field model EGM2008 has been used to investigate the structure of the crust. A regional/residual separation is performed using upward continuation and polynomial separation methods. The results from this operation show a similarity between the regional anomalies resulting from both methods. The regional anomaly maps present an increasing gradient trending ENE-WSW above and below latitude 5?N. Moreover, six nearly parallel profiles were drawn on the CVL in addition to two other profiles at the northern edge of Congo craton. These profiles were used to estimate the depths of the Moho discontinuity and some shallow sources by the means of the Bouguer and the residual anomalies respectively. The results show that the Moho discontinuity depths vary from 19 - 25 km (under Mount Cameroon) to 28 - 34 km (in Kumbo), while the southern neighbouring zone presents a Moho discontinuity depth ranging between 23 - 31 km (in Ngambe) and 22 - 32 km (in Eseka). These findings agree with the previous seismic and gravity researches lead in the area. EGM2008 is therefore a reliable tool to investigate the subsurface structures.展开更多
文摘The succession of tectonic phenomena in the South-West Cameroon area suggests that structures from the upper mantle infiltrated and took advantage of the cracks and fractures left by these phenomena to get closer to the earth’s surface. However, the intrusive structures closest to the surface remain poorly known. The objective of this work is to improve the knowledge related to the interpretation of gravity data in order to characterise the near-surface intrusive bodies in the South-West Cameroon area, and then analyse their mining and geothermal implications. To achieve this objective, the indirect, inverse and normalized standard deviation (NSTD) methods were used. The NSTD method was used to detect the contours of the intrusive bodies. The indirect method (spectral analysis) was used to determine the depths of the interfaces of three intrusive bodies, one located on the Bipindi-Ebolowa I axis (G5), the other on the Eseka-Pouma axis (G8) and the last on the Bokito-Monatele axis (G11). The results obtained show roofs located between 0 and 0.61 km, between 0 and 0.37 km and between 0 and 0.73 km for the G5, G8 and G11 bodies, respectively. Finally, the application of the 2D inversion method allowed us to estimate the density contrasts of the intrusive bodies (G5, G8 and G11). The superposition of the intrusive bodies detected by the NSTD with the geological and mineral resources map, as well as an analysis of the results obtained, gave indications of interesting zones for mining prospecting and for the search for geothermal reservoirs.
文摘The tectonic study based on geophysical data has been carried out in Sub-Himalayas in Azad Jammu and Kashmir and northern Pakistan. A series of thin skinned and thick skinned faults have been delineated in the investigated area on the basis of present study. In the study area compressional stresses caused by the collisional of Indian and Eurasian plates developed the northwestsoutheast trending faults which are Shaheed Gala thrust, Bagh basement fault, Kashmir boundary thrust and Kawai fault or Indus Kohistan seismic zone. The crustal thickness increases towards north due to the stacking of the thrust sheets along these faults. The Murree Formation thrusts over the Si- waliks molasse along the Shaheed Gala thrust. This fault dips at an angle of 43° northeast and joins the thick skinned Bagh basement fault in subsurface which are penetrated up to Moho depth. In the northeast of Bagh basement fault the northwest-southeast trending Kashmir boundary thrust has been delineated in the sedimentary-metasedimentary wedge which joins the Indus Kohistan seismic zone in the subsurface. The present study suggested that the Kawai fault which is running within Murree Formation cuts 16 km thick sedimentary-metasedimentary wedge and also joins the Indus Kohistan seismic zone in the subsurface.
文摘An academic geophysical research as a regional gravity survey was made during1994 in the Western White Nile to infer the shallow crustal structures in the area. The result ofthe survey was compiled as a Bouguer anomaly map with a contour interval of 2 X 10^(-5)m/s^2. It isfound that the negative residual anomalies are related to the Upper Cretaceous sediments (NubianSandstone Formation) filling all depressions in the Basement complex surface while the positiveresidual anomalies are attributed to the relatively shallow or outcropping Basement rocks and thesteep gravity gradients are resulting from the sharp contacts between the sedimentary infill and theBasement rocks. To define the geological structures in the area, 9 profiles were studied. For eachof the profiles, measured and computed Bouguer gravity anomalies, crustal density model, subsurfacegeology evaluation were performed. A G-model computer program was applied in the gravity modeling,which is based on the line-integral method of gravity computation. A geological/structural map wasproposed showing inferred sedimentary basins, faulting troughs and uplifted Basement block andtectonic trends. The basins are believed to be fault-controlled which developed by extensionaltectonics (pull-apart mechanism). As for the mechanism and cause of faulting, the area is consideredas a part of the Central Sudan rift system which had been subjected to several tectonic eventssince Early Cambrian to Tertiary times which resulted in the formation of several fracture systemsassociated with block subsidence, rifting and basin formation.
文摘In order to analyze and determine the geological structures of the Adamawa plateau, the terrestrial gravity data were combined to data computed from GGM02C gravity model. The dense gravity net obtained were further introduced into qualitative and quantitative interpretations. The resulting Bouguer anomaly map obtained from combined data shows NE-SW direction which nearly coincides with the main direction of the fractures affecting the basement in the region and indicates strong gradients marking the presence of discontinuities between heavy and negative gravity anomaly. In order to conduct the quantitative interpretation of the combined gravity data, three profiles were drawn on the residual Bouguer anomaly map and therefore were interpreted using spectral analysis method and 3D density inversion. The knowledge of the depth and density of the geological structures show an uplift of dense rocks under the granite-gneiss substratum. This dense material found in the ENE-WSW direction of the Adamawa Plateau is interpreted as basaltic intrusion probably resulting from tectonic processes. According to this study, the depths of 3.83 km and 9.62 km are the new values of depths obtained for futures investigations in the Adamawa plateau.
文摘The study area is located in the south western Cameroon and includes part of the Cameroon Volcanic Line (CVL). Volcanic activity has been recorded in this area, precisely on the Mount Cameroon which recently erupted in 2002. In addition, deadly carbonic gas was emitted by crater lakes (Monoun and Nyos) in 1984 and 1986 respectively. Potential field model EGM2008 has been used to investigate the structure of the crust. A regional/residual separation is performed using upward continuation and polynomial separation methods. The results from this operation show a similarity between the regional anomalies resulting from both methods. The regional anomaly maps present an increasing gradient trending ENE-WSW above and below latitude 5?N. Moreover, six nearly parallel profiles were drawn on the CVL in addition to two other profiles at the northern edge of Congo craton. These profiles were used to estimate the depths of the Moho discontinuity and some shallow sources by the means of the Bouguer and the residual anomalies respectively. The results show that the Moho discontinuity depths vary from 19 - 25 km (under Mount Cameroon) to 28 - 34 km (in Kumbo), while the southern neighbouring zone presents a Moho discontinuity depth ranging between 23 - 31 km (in Ngambe) and 22 - 32 km (in Eseka). These findings agree with the previous seismic and gravity researches lead in the area. EGM2008 is therefore a reliable tool to investigate the subsurface structures.
