Eburnean/Trans-Amazonian orogeny in the Nyong complex of southwestern Cameroon: Meta-basite geochemistry and metamorphic petrology

• Published in: Journal of African earth sciences (1994) 2022-06, Vol.190, p.104515, Article 104515
• Main Authors: Owona, Sébastien, Schulz, Bernhard, Minyem, Dieudonné, Ratschbacher, Lothar, Tchamabe, Boris Chako, Olinga, Jean Bosco, Ondoa, Joseph Mvondo, Ekodeck, Georges Emmanuel
• Format: Article
• Language: English
• Subjects: Central Africa; Eburnean/Trans-Amazonian orogeny; Geochemistry of oceanic lithosphere; Metamorphic petrology; Nyong complex
• ISSN: 1464-343X; 1879-1956
• DOI: 10.1016/j.jafrearsci.2022.104515

New and published geochemical, petrologic, and geo-thermobarometric data of meta-basites were combined to constrain the geodynamic evolution of the Paleoproterozoic Nyong complex (NyC) in southwestern Cameroon, a part of the Central African tectonic belt. Their geochemical signatures, including (La/Yb)N = 0.53–56.26, slightly positive Eu anomalies (0.21–1.04), abundance of Pb and U, negative Nb–Ta anomalies, and REE depletion, suggest various degrees of partial melting of mostly spinel-bearing mantle sources. In addition, the meta-basite protoliths can be classified as IAB-, E-MORB-, N-MORB-, and exceptionally OIB-compositional types with minor crustal contamination. Petrologically, the meta-basites are characterized by coronitic textures, marked by microblasts and porphyroblasts of garnet surrounded by plagioclase or by both plagioclase and clinopyroxene, indicating metamorphic recrystallization under decompression. Our new geo-thermobarometric data outline various segments of an overall clockwise pressure‒temperature path. In the different meta-basite samples, the pressure peak at eclogite-facies conditions (∼625 °C, 11.7 kbar) was followed by nearly isobaric heating to amphibolite-facies conditions (600–690 °C, 11.5 kbar) or decompression and heating to amphibolite- (∼740 °C, 10.8 kbar) and granulite-facies (∼800 °C, 10.0 kbar) conditions. The retrograde path evolved from granulite- (850–750 °C, 11.3–7.6 kbar) and amphibolite- (790–550 °C; 12.4–3.0 kbar) to epidote-amphibolite- (∼600‒490 °C, 8.0–7.6 kbar) and greenschist-facies (∼400 °C, 4.2 kbar) conditions. Combining the new with published, in general high to middle temperature-middle pressure data from various rock types, with published high temperature-high pressure data from eclogites highlights distinct burial-exhumation paths for the NyC rocks: these paths document a clockwise pressure-temperature evolution, typical for a collisional setting associated with the Rhyacian-Orosirian Eburnean/Trans-Amazonian orogeny in Cameroon. The eclogite data outline a deep burial–isothermal decompression evolution, typical for a subduction setting predating the collisional setting. [Display omitted] •Nyong complex contains the suture zone between the Congo and the São Francisco cratons.•Paleoproterozoic Nyong complex provides a record of the Eburnean orogeny.•Nyong meta-basite protoliths derived from various IAB, E-MORB, N-MORB and OIB sources.•Nyong meta-basites were overprinted in subduction and continental co