Staff directory
Jean-Paul Liégeois
Earth Sciences
Geodynamics and mineral resources
Geodynamics and mineral resources
Publication details
Kwekam, M., Affaton, P., Bruguier, O., Liégeois, J.P., Hartmann, G. & Njongfang, E. 2013. ‘The Pan-African Kekem gabbro-norite (West-Cameroon), U-Pb zircon age, geochemistry and Sr-Nd isotopes: Geodynamical implication for the evolution of the Central African fold belt’. Journal of African Earth Sciences 84: 70-88. Amsterdam : Elsevier. DOI: http://dx.doi.org/10.1016/j.jafrearsci.2013.03.010. I.F. 1.219.
Article in a scientific Journal / Article in a Journal
The Kekem shoshonitic gabbro-norite association is part of the high-K calc-alkaline (HKCA) post-collisional
magmatism, a major feature of the Pan-African Belt in Cameroon. LA-ICP-MS U–Pb zircon analyses
provide an age of 576 ± 4 Ma for the Kekem complex. This age is interpreted as dating the emplacement
of the massif during the waning stage of the Pan-African orogeny. The latter is related to dextral movements
along the Central Cameroon Shear Zone (CCSZ).
The REE patterns display enriched LREE (LaN/YbN = 14.2–23.5) while HREE present a nearly flat profile
(DyN/YbN = 1.3–1.7), and the La/Sm and Sm/Yb ratios led to propose that the Kekem gabbro-norites have
been derived from the partial melting of a garnet-spinel lherzolite mantle source. The negative Nb–Ta and
Ti anomalies and the positive Pb anomalies indicate that this mantle source was modified by contribution
of a subduction-related material. The low Ce/Pb (2.6–10.4) and Th/Yb ratios associated to high Ba/La
ratios, indicate that source enrichment could be related to slab derived fluids. As a whole, the Kekem geochemical
features suggest that primary gabbro-noritic magmas derived from a subduction-modified
mantle source (metasomatised lithospheric mantle). Moderately high 86Sr/87Sr initial ratios (0.7068–
0.7082), low eNd (5 to 9) and old Nd TDM model ages (1.6–1.8 Ga) are interpreted to result from contamination
of Neoproterozoic mantle by the Paleoproterozoic crust.
The ca. 576 Ma movements along the CCSZ are related to a Neoproterozoic metacratonization of the
northern margin of the Congo craton during the Pan-African orogeny. This metacratonization led to vertical
planar lithospheric delamination along lithospheric transcurrent faults, asthenospheric uprise and
partial melting of the Paleoproterozoic lithospheric mantle.