Understanding the Meaning of the Positive Bouguer Anomaly of Waza (Northernmost Cameroon, Central Africa)

Eyike Albert,Lordon Djieto Anatole Eugene,Nguimbous-Kouoh Jean Jacques,Basseka Charles Antoine,Tabod Charles Tabod,Zanga-Amougou Alain

doi:10.4236/gep.2019.76005

Eyike Albert, Lordon Djieto Anatole Eugene + Show 4 more

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https://doi.org/10.4236/gep.2019.76005

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Abstract

Gravity and magnetic data were analyzed in conjunction with available geological data to determine the origin of observed positive gravity anomaly at Waza and its possible relationship to mafic intrusions. The data analysis includes the construction of a Bouguer gravity anomaly, isostatic residual gravity anomaly, total magnetic gradient and Euler solutions maps, and two and one-half dimensional gravity models. A positive gravity anomaly that occurs in Waza has amplitude of 35 mGal and can be separated into two parts. The top of the disturbing body causing the anomaly cannot be deeper than 4 km. We believe the anomaly is probably caused by a body of basaltic rocks lying at the upper surface of the Precambrian basement and originate from a self-propagating disturbance of magmatic loads on a pre-existing zone of lithospheric weakness. Melt migration might have been aided by tectonic and flexural stresses, such that the intrusion is limited in extent to the melting region of the plume and did not reach the surface. The model calculated to satisfy the observed anomaly consists of a 2.5 Km-thick slab underlain by a 10.5 km deep column. This model is interpreted to represent a sheet or saucer-like mafic intrusion that has a thick deep feeder. Detailed geophysical studies would be necessary to locate any possible economic occurrences.

Highlights

Geophysical data provide information about geological features which are hidden under the overburden and are not observable by conventional geological mapping
Detailed analyses and interpretation realized by combining existing 2D reflection seismic and Gravity/Magnetic data of the Logone Birni Basin (LBB) in the West and Central African Rift System (WCAS) have revealed the distribution of buried volcanic bodies as well as their relationships with the structural and tectonic evolution of this basin
The geological and petrophysical data established for the area (Eyike & Ebbing, 2015; Loule & Pospisil, 2013), and the calculated Euler depths (Figure 3) considerably limit the number of possible models

Summary

Introduction

Geophysical data provide information about geological features which are hidden under the overburden and are not observable by conventional geological mapping. The volcanic bodies within the Lower Cretaceous are either lying directly on basement or are mainly interbedded with the contemporaneous sediments, whereas, the Upper Cretaceous bodies are morphologically expressed in the forms of dykes and sills (Loule & Pospisil, 2013) Despite this intense scientific activity, the existence of a positive Bouguer anomaly seen on all Bouguer maps, and associated with the Waza area has never been discussed. 130 - 118 Ma) which are relatively thick and do not allow the geological surface expression of this positive anomaly These small basins contain interstratified alkali basalt flows, associated with dolerite dykes and sills as well as post sedimentary intrusive igneous bodies which cut through the sedimendary sequence (Brunet et al, 1988; Loule et al, 1997). The aim of this study is to determine the detailed depth information of anomalous sources of Waza and explain its positive gravity anomaly

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