b'The origin of the Bangui magnetic anomalyFeaturedefine a mean ENE-WSW tectonic direction (Ngako etal. 2003;by the POGO satellite, highlights the presence of a magnetic Toteu etal. 2004) similar to that of the BMA. body buried in the crust. In accordance with this hypothesis Dorbath etal. (1981); Dorbath etal. (1985), based on seismic Previous studies investigations, located the top of the potential source at 3 km and the base at 40 km in the Bangui locality. Similarly, the fact The scientific issues related to the BMA are discussed accordingthat a negative Bouguer anomaly of about -20 mGals coincides (1) the aspects related to the geological context in Cameroonwith the magnetic anomaly implies, according to Regan and and Central African Republic; (2) the development of recentMarsh (1982) a rooting of the sources in the upper mantle. databases and (3) the complexity of some lithosphericAnother hypothesis is the existence according to Girdler etal. structures. (1992); Ravat etal. (2002) of a crater impact nearly 800 km wide and centred in Central African Republic.The BMA is defined as a massive aberration revealed by various satellite (POGO, MAGSAT, CHAMP, SWARM), airborneDiscussion on the origin of the BMA have evolved over time. and ground missions. The name derives from the capital ofThe different geological and extra-terrestrial hypotheses were the Central African Republic Bangui, where the minimumdiscussed by Boukeke (1994) based on information on the magnetic intensity was observed. From the MAGSAT to SWARMtopography, global tectonics, seismology, crustal structure and satellite missions in the 1950s to the present day, the BMAthe nature of the rocks. According to Marsh (1977) and Boukeke as mapped in the intra-continental domain also extends to(1994) the theory of a crater impact cannot be accepted because Cameroon (Figure1). Observations made by CHAMP (Mausno typical structure is recognisable. The idea of an intracrustal etal. 2009; Meyer etal. 2017) and SWARM (Sabaka etal. 2018)origin or sources rooted in the sub-continental mantle would satellite missions show that the geology of Cameroon andbe most likely, assuming that the BMA is caused by intrusions the Central African Republic is dominated by this giganticof mafic or ultra-mafic rocks in the crust. This hypotheses was magnetic anomaly, which appears to have three main lobes:challenged by Klokonick etal. (2010), who by analysing gradient a southern lobe observed in Cameroon; and the central andzones based on EGM2008 data in areas where meteorite upper lobes observed in Central African Republic. Although thecraters were suspected defined a circular surface similar to Central African Republic has already seen a number of studiesthat described by Ravat etal. (2002) and earlier by Girdler etal. describing and speculating on the source of the anomaly(1992). These developments demonstrate the conundrum to be (Godivier etal. 1980; Girdler etal. 1992; Hemant and Maus 2005;solved in understanding the sources of this anomaly. The results Ouabego etal. 2013), the part of the anomaly within Cameroonobtained from geological modelling from the CHAMP satellite has yet to be explored and characterised in order to (1) mapmission data (Hemant and Maus 2005) as well as petro-physical lithospheric structures in detail; (2) study the behaviour ofstudies on rocks samples combined with magnetic field data the BMA; (3) analyse the crustal structure; (4) determine the(Ouabego etal. 2013) have suggested that the sources of the geotectonic context of the evolution of the crust in relation toBMA are related either to metamorphic or mafic rocks.the emplacement of an anomaly of such magnitude and (5) establish relationships between the mineral resources, the BMA and the basement formations. One of the major and essentialThe contribution of geophysics to the characterisation large-scale concerns is the origin of the BMA. of lithospheric structures around the Bangui magnetic anomalyThe BMA is known as the second largest magnetic anomaly in the world and the largest in Africa (Godivier etal. 1962; GodivierGround gravity data are scarce in central Africa. Many etal. 1980; Ravat 1989; Meyer etal. 2017). The BMA in the intra- organisations such as the BGI (International Gravimetric Bureau) continental domain covers nearly two thirds of the Precambrianare working to produce gravity grids that combine the available formations of the Central African Republic. Based on ground,ground gravity data (Ex-ORSTOM or IRD) and satellite data, or airborne and satellite magnetic data, detailed mapping of thissatellite-only gravity data. These gravity grids replace terrestrial anomaly was possible. Godivier etal. (1962) estimated the spatialmeasurements where the accuracy is uncertain because of extension of this anomaly as well as its relationship with surfacetopography, vegetation and accessibility - factors that have rocks from ground measurements. The U.S. Bureau of Navalgreatly influenced the acquisition of terrestrial data (Figure 3). Oceanography, through the MAGNET project on a profile ofThere are geographical areas where it has not been possible about 3 km long, had observed a dipole anomaly of more thanto carry out measurements and thus to constrain lithospheric 1000 nT. The COSMOS 49 satellite mission for the very first timestructures.in 1964 reported an anomaly of -40 nT at an altitude of nearly 350 km (Benkova 1973). The POGO (Polar Orbiting GeomagneticIt is not easy to appreciate the contribution of satellite data Observatory) satellite mission similar to COSMOS 49 betweenrelative to the contribution of the terrestrial data in many of the 417 and 499 km altitude had revealed an intensity of -20 nT forgrids derived from the combined ground, marine and airborne the same anomaly (Benkova 1973). The first anomaly map ofgrid gravity data (WGM2012, EGM2008, XGM 2019). This creates the global field from the MAGSAT mission data at an altitude ofa real problem of the spatial representativeness of grids derived 375 km showed a minimum of -22 nT. At this scale the BMA isfrom combined measurements, compared with grids derived one of the most intense anomalies with a wavelength of nearlyfrom the ground-only gravity data, which have been used in 1200 km and a mean ENE-WSW orientation from the AtlanticCameroon to map lithospheric structures. The first ground coast to longitude 30E (Boukeke 1994). gravity campaigns (1960 to 1967) were carried out by ORSTOM (Office des Recherches Scientifiques pour les Territoires dOutre-The origin of the BMA is still not understood. Two theories haveMer) known today as the IRD. These campaigns covered an been proposed: meteoritic and geological. Godivier (1980), byarea of ~519 600 km2 with a network of 3600 gravity stations, superimposing the magnetic anomaly maps in Central Africafor an average density of 357 points per square degree. These resulting from the analysis of terrestrial data at 525 km altitudecampaigns led to the elaboration of the first Bouguer gravity 45 PREVIEW FEBRUARY 2022'