Aeromagnetic data for center-east Cameroon between the latitudes 3.5° to 4.5°N and longitudes 12° to 12.5°E are used to further study the subsurface area of this part of the geological Province of ...Aeromagnetic data for center-east Cameroon between the latitudes 3.5° to 4.5°N and longitudes 12° to 12.5°E are used to further study the subsurface area of this part of the geological Province of Central Africa and the Congo Craton. The GIS and GEOSOFT v6.5 softwares are used to treat the data. This analysis enabled us to explore our study area from surface right to the base. The Tilt Angle method is used to delineate geological structures and to estimate the depth. The Euler’s deconvolution method is used to estimate the specific depth of structural contacts. We estimate the northern boundary of the Congo Craton and southern boundary of the Pan-African starting from 3°7'N of West to 3°75'N of East. Its depth is estimated around 2.6 km for deep and 0.1 km for shallow while the direction is WSW-ENE and the NW slope varies from 30° to 60°. We obtain that main and minor lineaments exist throughout, from the surface to the base of the area with their principal direction being SW-NE. We also obtain the vertical gradient contact and the quasihorizontal contact. This is proof of the subduction of the Pan-African belt under the Congo Craton due to the intense collision which caused the rejuvenation of the crust. The main consequence of this collision is the formation of pudding and fold structures, beginning from the superficial part right to the base and which caused the intrusion of schistose, chlorite-schist, quartzite in the micaschist and the intrusions of gneiss and garnetiferous schist in the migmatite. In our study, we highlight the presence of 37 major and 523 minor lineaments that localize the circulation of minerals. The probable slope of the lineaments in the northern part of the region varies from 30° to 60° in a SE direction while in the southern part, and it varies from 30° to 60° in a NW direction.展开更多
The DJADOM-ETA area is in south-eastern of Cameroon, within the Congo Craton (CC) formations and composed of gneiss and amphibolite, migmatites and intrusive rocks. Few geophysical studies have been carried out over s...The DJADOM-ETA area is in south-eastern of Cameroon, within the Congo Craton (CC) formations and composed of gneiss and amphibolite, migmatites and intrusive rocks. Few geophysical studies have been carried out over surrounding areas, but no investigation on the study area. The existence of aeromagnetic data covering the study area has motivated the application of a multiscale approach for tectonic features identification. The aim of this work is to interpret Aeromagnetic Data for Geological and Structural Mappings in the southeastern Cameroon. The GIS and GEOSOFT v8.4 softwares are used to treat data of Compagnie Minière du Cameroun getting in February 2012. The Tilt Angle method is used to delineate geological structures and to estimate the depth. The Euler’s Deconvolution method is used to estimate the specific depth of structural contacts. The presence of bifurcations, accompanied by virgations, leading to the occurrence of several faults. Principal lineaments are determined with the main direction being ESE-WNW and E-W for the minor lineaments. The study highlights two major faults: ESE-WNW and ENE-WSW, where the former dominates, what could be called the geological accident of ETA. The Euler’s Correlation and Tilt derivative contact map shows that most of the faults are vertical contacts. The geometrical description of this structure suggests an open synclinal transposed on vertical foliations: the major fault at the DJADOM axis is quasi-parallel to the Northern limit of the CC and parallel to the Sanaga Fault (SF) and the Central Cameroon Shear Zone (CCSZ). The features show a base strongly affected by tectonic which characterizes the transition between the zone from the CC and the belt from folds of the Pan-African. Also, the presence of the network characterizes the subsurface undulation in this study area: the intrusion of sandstone ochre quartz and schist of the Bek complex, the dolerite of the doleritic complex, and the silver micaschiste and ore quartzite in the base complex. On the TMI anomalies map, several places show high susceptibility contrasts, which is an indication of strong magnetization. Geological indicators point to inferred magnetite, dolerite and ochre schist quartzite which have a strong magnetization in this zone. The presence of weakly magnetized anomalies would be due to the migmatites of the base complex series. This study improved the knowledge of the subsurface structure of this area. It highlighted two major and minor faults. TMI anomalies map, in several places shows high susceptibility contrasts, which is an indication of strong magnetization.展开更多
We explore the physical phenomenon of acoustic waves induced at the interface between two different anisotropic rock media.Specifically,one medium is a transversely isotropic medium with a vertical axis of symmetry(VT...We explore the physical phenomenon of acoustic waves induced at the interface between two different anisotropic rock media.Specifically,one medium is a transversely isotropic medium with a vertical axis of symmetry(VTI medium)and the other one is a transversely isotropic medium with a tilt axis of symmetry(TTI medium).By solving the Kelvin-Christoffel equation,an eighth-order polynomial is established for reflection and refraction angles,which is confirmed from SnelFs law.Three types of analytical expressions of the polarization coefficients of the induced waves are obtained corresponding to different incident angle regions.An effective algorithm has been developed for numerical analysis of the polarization coefficients.Applying characteristic anisotropic parameters reported in the literature,the influencing factors on reflection and refraction coefficients are analyzed,e.g.,the anisotropy,the tilt-angle of rock-layer,and the incident-angle.The calculated reflection and refraction coefficients have been rechecked for energy conservation.展开更多
文摘Aeromagnetic data for center-east Cameroon between the latitudes 3.5° to 4.5°N and longitudes 12° to 12.5°E are used to further study the subsurface area of this part of the geological Province of Central Africa and the Congo Craton. The GIS and GEOSOFT v6.5 softwares are used to treat the data. This analysis enabled us to explore our study area from surface right to the base. The Tilt Angle method is used to delineate geological structures and to estimate the depth. The Euler’s deconvolution method is used to estimate the specific depth of structural contacts. We estimate the northern boundary of the Congo Craton and southern boundary of the Pan-African starting from 3°7'N of West to 3°75'N of East. Its depth is estimated around 2.6 km for deep and 0.1 km for shallow while the direction is WSW-ENE and the NW slope varies from 30° to 60°. We obtain that main and minor lineaments exist throughout, from the surface to the base of the area with their principal direction being SW-NE. We also obtain the vertical gradient contact and the quasihorizontal contact. This is proof of the subduction of the Pan-African belt under the Congo Craton due to the intense collision which caused the rejuvenation of the crust. The main consequence of this collision is the formation of pudding and fold structures, beginning from the superficial part right to the base and which caused the intrusion of schistose, chlorite-schist, quartzite in the micaschist and the intrusions of gneiss and garnetiferous schist in the migmatite. In our study, we highlight the presence of 37 major and 523 minor lineaments that localize the circulation of minerals. The probable slope of the lineaments in the northern part of the region varies from 30° to 60° in a SE direction while in the southern part, and it varies from 30° to 60° in a NW direction.
文摘The DJADOM-ETA area is in south-eastern of Cameroon, within the Congo Craton (CC) formations and composed of gneiss and amphibolite, migmatites and intrusive rocks. Few geophysical studies have been carried out over surrounding areas, but no investigation on the study area. The existence of aeromagnetic data covering the study area has motivated the application of a multiscale approach for tectonic features identification. The aim of this work is to interpret Aeromagnetic Data for Geological and Structural Mappings in the southeastern Cameroon. The GIS and GEOSOFT v8.4 softwares are used to treat data of Compagnie Minière du Cameroun getting in February 2012. The Tilt Angle method is used to delineate geological structures and to estimate the depth. The Euler’s Deconvolution method is used to estimate the specific depth of structural contacts. The presence of bifurcations, accompanied by virgations, leading to the occurrence of several faults. Principal lineaments are determined with the main direction being ESE-WNW and E-W for the minor lineaments. The study highlights two major faults: ESE-WNW and ENE-WSW, where the former dominates, what could be called the geological accident of ETA. The Euler’s Correlation and Tilt derivative contact map shows that most of the faults are vertical contacts. The geometrical description of this structure suggests an open synclinal transposed on vertical foliations: the major fault at the DJADOM axis is quasi-parallel to the Northern limit of the CC and parallel to the Sanaga Fault (SF) and the Central Cameroon Shear Zone (CCSZ). The features show a base strongly affected by tectonic which characterizes the transition between the zone from the CC and the belt from folds of the Pan-African. Also, the presence of the network characterizes the subsurface undulation in this study area: the intrusion of sandstone ochre quartz and schist of the Bek complex, the dolerite of the doleritic complex, and the silver micaschiste and ore quartzite in the base complex. On the TMI anomalies map, several places show high susceptibility contrasts, which is an indication of strong magnetization. Geological indicators point to inferred magnetite, dolerite and ochre schist quartzite which have a strong magnetization in this zone. The presence of weakly magnetized anomalies would be due to the migmatites of the base complex series. This study improved the knowledge of the subsurface structure of this area. It highlighted two major and minor faults. TMI anomalies map, in several places shows high susceptibility contrasts, which is an indication of strong magnetization.
基金the Na-tional Natural Science Foundation of China(Grant No.41974130)the Physical Sciences Division at The University of Chicago.
文摘We explore the physical phenomenon of acoustic waves induced at the interface between two different anisotropic rock media.Specifically,one medium is a transversely isotropic medium with a vertical axis of symmetry(VTI medium)and the other one is a transversely isotropic medium with a tilt axis of symmetry(TTI medium).By solving the Kelvin-Christoffel equation,an eighth-order polynomial is established for reflection and refraction angles,which is confirmed from SnelFs law.Three types of analytical expressions of the polarization coefficients of the induced waves are obtained corresponding to different incident angle regions.An effective algorithm has been developed for numerical analysis of the polarization coefficients.Applying characteristic anisotropic parameters reported in the literature,the influencing factors on reflection and refraction coefficients are analyzed,e.g.,the anisotropy,the tilt-angle of rock-layer,and the incident-angle.The calculated reflection and refraction coefficients have been rechecked for energy conservation.
