Effective elastic thickness and crustal thickness variations in west central Africa inferred from gravity data

Abstract

International audienceThe west central African region is characterized by various geological features: Cretaceous rifts (Benue), Tertiary domal uplift (Adamawa volcanic uplift), Tertiary-Recent volcanoes (Cameroon Volcanic Line or CVL), Tertiary sedimentary basins (Chad basins), and cratonic region (Congolese craton). In this study, we investigate the relationship between these tectonic features and the flexural rigidity of the lithosphere in Cameroon, in terms of effective elastic thickness (Te), by the use of the coherence function analysis. For that purpose, we use a new dataset of-32,000 gravity and topography points from Cameroon and the adjacent countries. The Te contour map deduced from this study shows a good relationship between the tectonic provinces and the rigidity of the lithosphere, the minima (14-20 km) are beneath the active rifted and volcanic areas (Benue, CVL, and Adamawa), and the maxima (-40 km) correspond to the Archean reworked unit in Congo. A spectral analysis of the gravity data is performed to determine the crust-mantle boundary in these tectonic provinces. The crustal thickness (Tc) contour map shows a variation from 14 km to about 45 km, consistent with other geophysical data. The lower values (14-20 km) are obtained in central Cameroon on the Adamawa uplift, and the highest values are found in southern Cameroon (Archean reworked Congolese craton). Comparing Te and Tc values shows that there is generally a positive correlation between the two parameters, with an exception in Chad where this correlation is rather negative

Evidence for the Upwelling of Mafic Bodies into the Upper Crust beneath the N40-50°E Branch of the Pan-African Central Cameroon Shear Zone from Gravity Studies

“…This method is well established and proved its usefulness in schemes of interpretation in gravity [35] …”

“…Geological map of the studied area (after [26], modified). [35]. All gravity measurements are tied to the International Gravity Standardization Network 1971 (IGSN71) datum after correction of luni-solar effect and instrumental drift.…”

Estimation of the Depth of Major Subsurface Discontinuities Beneath the Mount Cameroon Region, Central Africa, Based on New and Existing Gravity Data Analysis

“…On a smaller scale, we can cite the work of Ateba et al (2009) and that of Kenfack et al (2011). The studies of Poudjom Djomani et al (1995) were carried out in a regional framework, extended over several hundreds of kilometers, largely with evidence of deep structural contrasts, located in the upper mantle. The meaning attributed to gravity anomaly do not take into account the effect of gravitational density contrast due to the structure of the crust.…”

“…Many geophysical surveys have been effectuated to study of the Mount Cameroon region. These include studies across the country, such as the work of Poudjom Djomani et al (1995) with gravity data and those of Tokam et al (2010) using seismic data. On a smaller scale, we can cite the work of Ateba et al (2009) and that of Kenfack et al (2011).…”

Geometrical Characterisation of the Mamfe Basin, Cameroon, from the Earth, Gravitational Model (EGM 2008)

“…Abate Essi et al, 2017 used satellite derived geavity data to study the subsurface of Central Northern Cameroon with structural and mining implications, hence it was used in this research to determine the geometrical characteristics of the Mamfe basin. The ground gravity dataset from the ORSTOM database (Poudjom-Djomani et al, 1995) have been used in the basin (Fairhead et al 1991;Ndougsa-Mbarga, 2004;Ndougsa-Mbarga et al 2007), but its poor spatial resolution in the study area (since it follows only roads, Poudjoum et al, 1995) makes it not suitable for geometrical characterization. We therefore use the high resolution satellite-based Earth Gravitational Model 2008 (EGM2008) which has been corrected using the ETOPO1 to propose reliable values of the length, width and depth of the Mamfe basin and to give the shape of its basement.…”