International audienceThe 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

No abstract

No abstract

No abstract

The Dschang granites, SW Cameroon, are post-Panafrican granitoids, hosted in Paleoproterozoic orthogneiss in the Western domain of the Central African fold belt. They include coarse-grained K-feldspar biotite granite and fine-grained magnetite granite. Magnetite forms nodules surrounded by a quartzo-feldsparthic halo. Major and trace element data of both granites show high SiO2, Al2O3, total alkalis and Ba and low TiO2, MgO, P2O5 and Nb contents, conferring a fractionated I-type high-K alkali-calcic and weakly peraluminous character. Both granites are enriched in light rare earth elements and large ion lithophile elements, depleted in high field strength elements, and show a rare earth element pattern with Eu/Eu* = 0.3 to 0.9. Primitive mantle-normalized spidergrams display negative Nb, Ta and Ti anomalies, typical of their derivation from subduction-related post-collisional melt. Laser inductively coupled plasma mass spectrometry U–Pb data on zircons yielded crystallization ages of 578 +7/−11 Ma and 563+8/−3 Ma for the biotite and magnetite granites respectively. Inherited zircon (1991–1442 Ma), whole-rock Nd model ages in the range 2.1–1.9 Ga, highly negative εNdt (−16 to −18) and initial 87Sr/86Sr ratios in the range 0.7075–0.7114, support the remobilization of a Paleoproterozoic crust. The felsic magmas were probably produced by partial melting of Paleoproterozoic orthogneiss host rocks, under oxidizing conditions. Magnetite granite is also known from the Nkambé region. Such granites from both the Dschang and Nkambé regions suggest the presence of a Paleoproterozoic domain rich in iron mineralization. This domain potentially represents a Cu, Pb, Zn and Mo metallogenic province, heavily reworked during the Pan-African orogeny.