Gravity Data Interpretation in the Northern Edge of the Congo Craton, South-Cameroon

Gravity data in the southern Cameroon are interpreted to better understand the organization of underlying structuresthroughout the northern edge of the Congo craton. The Bouguer anomaly maps of the region are characterized by an elongated trending trending negative gravity anomaly which correspond to a collapsed structure associated with a granitic intrusion beneath the cente center of the region r of the region of the region and limited by fault systems. �e applied 3�D gravity modelling and inversion in order to obtain the 3D density structure of the area. Our result demonstrated that observed gravity anomalies in the region are associated to tectonic structures in the subsurface. The resulting model agrees with the hypothesis of the existence of a major continental collision zone between the Congo Craton and the Pan�African belt. The presence of deep granulites structures in the northern part of the region expresses a continental collision

Interpretação gravimétrica na Borda Norte do Cráton do Congo, Sul de Camarões

Gravity data in the southern Cameroon are interpreted to better understand the organization of underlying structures throughout the northern edge of the Congo craton. The Bouguer anomaly maps of the region are characterized by an elongated SW-NE trending negative gravity anomaly which correspond to a collapsed structure associated with a granitic intrusion beneath the center of the region and limited by fault systems. We applied 3-D gravity modelling and inversion in order to obtain the 3-D density structure of the area. Our result demonstrated that observed gravity anomalies in the region are associated to tectonic structures in the subsurface. The resulting model agrees with the hypothesis of the existence of a major continental collision zone between the Congo Craton and the Pan-African belt. The presence of deep granulites structures in the northern part of the region expresses a continental collision.Um conjunto de dados gravimétricos, provenientes do sul de Camarões, foram interpretados para o melhor entendimento das estruturas em sub superfície na borda norte do Cráton do Congo. Os mapas de anomalia Bouguer desta região foram caracterizados por uma anomalia gravimétrica negativa de direção SW-NE, que corresponde a uma estrutura de colapso associada com uma intrusão granítica, abaixo do centro desta região, e que está limitada por um sistema de falhas. Foram utilizados métodos de modelagem gravimétrica 3 D e inversão, para se obter uma estrutura densa 3-D desta área. Os resultados demonstraram que as anomalias gravimétricas observadas na região estão associadas com estruturas tectônicas em sub superfície. O modelo resultado está em consonância com a hipótese de existência de uma zona de colisão continental principal entre o Cráton do Congo e o Cinturão Pan-Africano. A presença de estruturas granulíticas profundas na borda norte desta área indica uma colisão continental

The Local Geoid Model of Cameroon: CGM05

This paper deals with the geoid determination in Cameroon by a gravimetric solution. A number of data files were compiled for this work, containing about 62,000 points on land and ocean areas and also including data derived from satellite altimetry. A hybrid global geopotential model (EGM-GGM) supplied the longer wavelength components of this geoid model, CGM05. This global model is obtained by adjusting the GRACE model GGM02C to degree and order 360 using the harmonic coefficients of the model EGM96 beyond the maximal degree 200 of GGM02C. The medium wavelength components were computed using the best gridded residual gravity anomalies, by integration in Stokes’ formula. The digital terrain model GLOBE contributed to its short wavelength components. The residual terrain model (RTM) was applied to first determine a quasi-geoid model. This intermediate surface was converted to the geoid using a grid of simple Bouguer gravity anomalies. The validation of CGM05 is based on comparisons to global and regional geoids. A GPS/levelling geometric geoid computed in a small part of the target area shows that the absolute accuracy of this local geoid model is 14 cm. After a four-parameter fitting to the GPS/levelled reference surface, this absolute accuracy reduced to 11 cm

Accurate gravity anomaly interpolation: a case-study in cameroon, central africa

Many treatments in geodesy and geophysics require regularly gridded gravity anomalies. The gridding of gravity data needs interpolation. For the predicted data to be accurate, the smoothest type ofgravity anomaly should be used along with the most indicated prediction method. This paper presents the comparison of various prediction methods applied on different types of gravity anomalies andconsidering the relative geological complexity of the study area. Many algorithms are tested and the suitability of each type of anomaly and each prediction method discussed in a case-study in Cameroon (Central Africa), using a set of 43,000 gravity data points to determine the must accurate prediction technique

Upper Mantle Structure beneath Cameroon from Body Wave Tomography and the Origin of the CVL

[1] The origin of the Cameroon Volcanic Line (CVL), a 1600 km long linear volcanic chain without age progression that crosses the ocean-continent boundary in west-central Africa, is investigated using body wave tomography. Relative arrival times from teleseismic P and S waves recorded on 32 temporary seismic stations over a 2-year period were obtained using a multichannel cross-correlation technique and then inverted for mantle velocity perturbations. The P and S wave models show a tabular low-velocity anomaly directly beneath the CVL extending to at least 300 km depth, with perturbations of −1.0 to −2.0% for P and −2.0 to −3.0% for S. The S wave velocity variation can be attributed to a 280 K or possibly higher thermal perturbation, if composition and other effects on seismic velocity are negligible. The near vertical sides of the anomaly and its depth extent are not easily explained by models for the origin of the CVL that invoke plumes or decompression melting under reactivated shear zones, but are possibly consistent with a model invoking edge-flow convection along the northern boundary of the Congo Craton lithosphere. If edge-flow convection in the sublithospheric upper mantle is combined with lateral flow channeled along a fracture zone beneath the oceanic sector of the CVL, then the oceanic sector can also be explained by flow in the upper mantle deriving from variations in lithospheric thickness

Evidence for precambrian faulting in the tibati-adamawa region of cameroon using the audiomagnetotelluric method

La falla de Adamawa es una estructura tectónica relacionada con la línea volcánica de Camerún. Se han obtenido datos ATM a lo largo de una superficie de casi 1,600 km2 alrededor de la ciudad de Tibati. El conocimiento geológico del área es escaso; los últimos datos se recopilaron hace 50 años. Este artículo describe las etapas principales, seguidas de la determinación de la firma electromagnética de la falla. Los resultados muestran numerosas zonas anómalas atribuidas a la zona de Cizalla. Todo ello nos permiten inferir la estructura de la resistencia eléctrica y hacen posible tener conocimiento acerca de la falla de Tibali. Estos resultados son preliminares a un estudio de la estructura de esta falla precámbrica. En este estudio se produjeron valores y variaciones importantes de la aparente resistencia. La falla de Tibati se caracteriza por su gran complejidad y estrechez. doi: https://doi.org/10.22201/igeof.00167169p.2011.50.2.13

Delineation of the northern limit of the Congo Craton based on spectral analysis and 2.5D modeling of aeromagnetic data in the Akonolinga-Mbama area, Cameroon

Se analizaron datos aeromagnéticos de la región Akonolinga–Mbama, con la finalidad de determinar la geología de subsuperficie de la zona. La interpretación de los datos disponibles, en forma de un mapa aeromagnético residual, muestra a esta vasta zona como magnéticamente tranquila, y las zonas complejas no se correlacionan con la geología de la superficie de la región. Dentro de esta zona magnética tranquila una zona negativa alta, anómala, alargada y circular parece significar la intrusión de una roca plutónica en las formaciones metamórficas de la región. Se utilizaron el análisis espectral y la modelación dimensional de 2 y medio (2½ -D) para determinar la profundidad de los cuerpos que lo causaron y analizar las rocas de origen a lo largo de tres perfiles que cruzan las zonas en estudio. Se obtuvieron modelos de las intrusiones graníticas de diversas zonas, lo cual parece significar algunas fallas poco profundas a lo largo de las zonas de contacto. Esto nos permitió delimitar el margen norte del Congo Cratón, con lo cual distinguimos las formaciones cratónicas de la faja Panafricana plegada. Parte de la faja se ha extendido sobre la parte norte del Congo Cratón en Camerún. doi: https://doi.org/10.1016/S0016-7169(14)71486-

Crustal structure beneath Cameroon from EGM2008

We used the Earth Gravitational Model (EGM2008) data sets to analyze the regional gravity anomalies and to study the underground structures in Cameroon. We first created a high-resolution Free-Air anomaly database, then corrected the gravity field of the topographic effect by using ETOPOl DEM with a resolution of 0.01° to obtain the Bouguer anomaly, then applied a multi-scale wavelet-analysis technique to separate the gravity-field components into different parts of shallow-to-deep origins, and finally used the logarithmic power spectrum technique to obtain detailed images and corresponding source depths as well as certain lateral inhomogeneity of structure density. The anomalies of shallow origin show successive elongated gravity “highs” and “lows” attributable to subsurface Tertiary and lower Cretaceous undulations. Our results are in good agreement with previous investigations

Hydrogeological activity of lineaments in Yaoundé Cameroon region using remote sensing and GIS techniques

Though Yaoundé zone is characterized by abundant rains, access to safe drinking water becomes a difficult activity, because of climate change and pollution caused by human activities. Lineament zones on the earth’s surface are important elements in understanding the dynamics of the subsurface fluid flow. However, good exposures of these features are always lacking in some areas around Yaoundé, characterized by thick alteration. During field surveys these conditions, in many cases, hinder the proper characterization of such features. Therefore, an approach that identifies the regional lineaments on remote-sensing images (Landsat Thematic Mapper and shaded digital terrain models), with its large scale synoptic coverage, could be promising. This paper aims to the structural organization of lineament network in the crystalline basement of Yaoundé from remote sensing data and characterize them by statistical and geostatistical techniques. The results were validated on the basis of the geological maps, the hydrogeological maps and the outcrop data. Statistical analysis of the lineaments network shows a distribution along the N0–10, N20–30, N40–60 and N140–150. The correlation between the productivity of high yield wells and the closest lineament confirms that these lineaments are surface traces of regional discontinuities and act as main groundwater flow paths

Petrographic, morpho-structural and geophysical study of the quartzite deposit in the central part of Pouma, Littoral-Cameroon

The characterization of the Pouma-Cameroon quartzite deposit with the aim of determining its lateral extension along the Douala-Yaoundé axis required, among other things, the examination of the petrographic and morpho-structural domain as well as the determination of the electrical properties of the formations in the study area. 24 vertical electrical sounding points were carried out using a Schlumberger type electrode configuration; also, 7 manual auger boreholes were carried out, these resulted on one hand in the following types of curves: KH, QH, AKH, H, HK, AK, HA, A; and on the other hand to lithological logs with a clayey sandy texture, gravelly clayey sand to lateritic. The calculation of the densities as well as the petro-structural studies made it possible to confirm the geological context of the study area. The various results obtained permitted us to locate the fresh quartzite formation at the center of the study area. It stretches along the Douala-Yaoundé axis over 1871.4 m for the fresh formation and 1991 m for the slightly altered formation