Archean tectonics in the sangmelima granite-greenstone terrains, Ntem Complex (NW Congo craton), southern Cameroon.

Abstract

Sangmelima granite-greenstone terrains (SGB) provide a new overview of the evolution of the Ntem Complex (South Cameroon), the northwestern part of the Congo Craton. The regional deformation is marked by a strong steep dips foliation and steeply plunging mineral-stretching. D 1 -related structures are folding and shearing by a D 2 deformation that is synchronous with extraction granitic dykes. D 1 -D 2 structures were developed during regional E-W sub-horizontal shortening under ductile conditions associated with steeply dipping principal stretching in a transpressive regime, progressive strain localization along strike-slip shear zones. Syn-D 1 mineral assemblages and high strain microstructures suggest that ductile deformation D 1 occurred under high-grade metamorphic conditions, whereas D 2 microstructures suggest a brittle deformation. The strain patterns in the SGB recorded a long-lasting Archean tectonic history within the Archean Ntem Complex (ca. 2.83-2.72Ga). Finally, some Archean structures were reactivated during a brittle deformation (D 3 ), likely during the Eburnean event.The Archean block in the north-western margin of the Congo Craton (Fig. 1a), corresponds to the Ntem-Chaillu Block (here after called

LA–ICP–MS zircon U Pb dating, Lu Hf, Sm Nd geochronology and tectonic setting of the Mesoarchean mafic and felsic magmatic rocks in the Sangmelima granite-greenstone terrane, Ntem Complex (South Cameroon)

“…Nevertheless, some zircon grains show low Th/U ratio (< 0.1) and display homogenous textures, typical of metamorphic or anatectic zircons (e.g., Dong et al, 2017). Considering the partial reset of the U\ \Pb isotope system during the Neoarchean crustal anatexis (Akame et al, 2020), the upper intercept age of 2758 Ma of our high-K granite sample JA-1 (Fig. 7f) could probably represent the crystallization age of the rock.…”

“…Johnson et al, 2018; reference therein). More recently Akame et al (2020) reported that the regional S 1 foliation (main structure of D 1 strain) were reworked by the D 2 deformation coeval with the second anatexis event materialized by melt migration along the C 2 shear zones and granitic dyke emplacement. Therefore, the age of 2744 ± 31 Ma is interpreted as the second stage of the anatexis coeval with the D 2 deformation event.…”

“…However, the high-K granitoids from Ebolowa yielded Pb\ \Pb zircon evaporation minimum ages ranging from 2687 ± 3 Ma to 2666 ± 2 Ma, which has been interpreted as a late Neoarchean tectono-thermal event (Tchameni et al, 2000). Available structural data indicate that the Ntem Complex was affected by two Archean deformation phases (D1, D2) and late D3 Paleoproterozoic event ca 2.1-2.0 Ga (Akame et al, 2018(Akame et al, , 2020Feybesse et al, 1998;Owona et al, 2011;Tchameni et al, 2000). D1 is marked by a N080°E to N120°E and NNW-trend subvertical foliation formed during the high-grade metamorphic condition.…”

“…In addition, field and structural analysis indicate that the Sangmelima Mesoarchean gneisses are variably migmatised and deformed together with supracrustal rocks during horizontal crustal shortening (Fig. 11a; Akame et al, 2020). At~2.75 Ga, partial melting of the charnockites-TTG crust generated the high-K granites, and melting migrated along shear zones during D2 transpression tectonics.…”

Seismogenic Fault Reactivation in Western Central Africa: Insights From Regional Stress Analysis

“…These cratonic blocks have underwent multiple episodes of large-scale brittle deformation which created large discontinuities within them. Akame et al (2020Akame et al ( , 2021 documented the presence of large NW-SE, NE-SW and E-W trending brittle and ductile shear zones in the Ntem-Chaillu block, inherited from Neoarchean orogenesis. Similar deformation were also reported in the laterally equivalent Souanké Archean rocks in the Ivindo region (Gatsé Ebotehouna et al, 2021;Loemba et al, 2022).…”