Tectonic evolution in the Archean Ntem Complex (NW CongoCraton, southern Cameroon) from 2.84-2.7 Ga;Contribution from LA–ICP–MS U–Pb zircon and EPMA U–Th– Pb monazite ages.

National audienceThis contribution examines the strain pattern of the Archean Ntem Complex,located in the northwestern part of the Congo Craton (southern Cameroon). We carrieda detailed field study coupled with aeromagnetic map for the two main greenstone belts(Sangmelima and Nyabisan), focusing on the geometry of structures as well askinematics, and identifying several lithological facies with distinct petrologicalcharacters. The time constraints of magmatism, metamorphism and deformation wereobtained by U–Pb LA–ICP–MS dating on zircon and EPMA U–Th–Pb dating onmonazite.The Nyabissan Greenstone Belt is dominated by sub-vertical transpressive shearzones with steeply plunging stretch lineations. There are vertical regional fabricdomains with sub- horizontal foliation domains suggesting a strain partitioning at aregional scale. Different generations of syntectonic mafic and felsic intrusions attest tolong-lasting progressive deformation.In the Sangmelima granite-greenstone belt (SGB), charnockites and TTG suites formedbetween~ 3155 and 2850 Ma. The gabbro intrusion was dated at 2866±6 Ma.Migmatization of the TTG-gneiss, coeval with a sub-horizontal shorteningsynmetamorphic D1 event, is dated around 2843–2820 Ma using U–Pb LA–ICP–MSon zircon and chemical U–Th–Pb EPMA dating on monazite. Syn-kinematicmonzogranite emplaced 2838±6 Ma ago. D2 is associated with the F2 folds and C2 shearzones coeval with the second anatexis period between ~2788–2722 Ma marked bythe emplacement of high-K granite that peaked at ~2750 Ma. Ages of migmatisationand syn-kinematic granites (2843 to 2722 Ma) suggest a long-lasting tectonic processin the Sangmelima area. Late Neoarchean granitic pegmatite/aplite dikes and/or veinsemplaced during the brittle deformation D3 and ANC protracted cooling between~2670–2550 Ma.A synthesis of all results leads to the reconstruction of the general structure for theNtem Complex, from the Paleo and Neoproterozoic to the Archean domains. Inaddition, a new model of Archean geodynamic evolution in the NW Congo Craton from3.32 Ga to 2.55 Ga is proposed