| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 4728925 | Journal of African Earth Sciences | 2013 | 19 Pages |
•Zircon U–Pb is using to date the Kekem gabbro-norite pluton.•Mineralogical assemblage of gabbro and norite is determined.•Geochemistry and isotopic data were performed to determine petrogenesis of this pluton.•Using combination of geochronogical and geochemical data to propose geodynamical setting.
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 εNd (−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.
