Rock magnetic investigation of possible sources of the Bangui magnetic anomaly

Mariane Ouabego (1, 2) , Yoann Quesnel (2) , Pierre Rochette (2) , François Demory (2) , E. M. Fozing (3) , T. Njanko (3) , Jean-Claude Hippolyte (2) , Pascal Affaton (2)

1 Laboratoire de Géosciences [Bangui]
2 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
3 Université de Dschang

The Bangui magnetic anomaly (BMA) is the largest lithospheric magnetic field anomaly on Earth at low latitudes. Previous studies investigated its geological source using constraints from satellite and ground magnetic field measurements, as well as from surface magnetic susceptibility measurements on rocks from the Panafrican Mobile Belt Zone (PMBZ). Here we combine magnetic field data modelling and rock magnetic property measurements (susceptibility and natural remanent magnetization, NRM) on many samples from this PMBZ and the surrounding formations. It reveals that NRM is a significant component of the total magnetization (Mt) of the BMA source, which reaches 4.3 A/m with maximum thicknesses of 38 and 54 km beneath the western and eastern parts of the BMA. Only the isolated and relatively thin banded iron formations and some migmatites show such Mt values. Thus we suggest that the thick BMA source may be composed either by overlapped slices of such metamorphic rocks, or by an iron-rich mafic source, or by a combination of these two geological structures.

Mots clés: Bangui magnetic anomaly; Magnetization; Geological source; Modelling; Banded iron formation

Domaines: Géophysique [physics.geo-ph]; Géophysique [physics.geo-ph]; Milieux et Changements globaux; Planétologie; Géologie appliquée

Mariane Ouabego, Yoann Quesnel, Pierre Rochette, François Demory, E. M. Fozing, et al.. Rock magnetic investigation of possible sources of the Bangui magnetic anomaly. Physics of the Earth and Planetary Interiors, 2013, 224, pp.11-20. ⟨10.1016/j.pepi.2013.09.003⟩. ⟨hal-00933326v2⟩