Age of the granulitic metamorphism of the Nyong complex in the west border of Congo Craton, South Cameroon

Abstract

Pressure and temperature conditions and electron microprobe analysis dating on monazite were conducted to investigate the age of the tectono-metamorphic events of Nyong Complex. The purpose of this work is to constrain P-T conditions and age to provide criteria for geodynamic models. The study area is made up of Paleoproterozoic metabasites, restricted Pan-African metasedimentary rocks and the rocks resulting from the melting of igneous rocks. This region displays a complex tectono-metamorphic evolution characterized by three phases of metamorphism associated with three deformational phases: The pre-D 1 phase (HP-HT: 784–860 °C, 12–13 kbar) implying its relationship with Archean. The D 1 phase (850 and 900 °C, 11–13 kbar) is a Paleoproterozoic event (1734 and 1893 Ma) that was developed under granulite facies metamorphic, implying that charnockitization took place in Paleoproterozoic. Charnockitization is a metamorphic process that transforms granitic rock into charnockite. The last stage D 2 (450–500 °C, 7–9 kbar) is Pan-African in age (577–677 Ma) and characterizes the amphibolite facies metamorphism (MP-MT). This implies that the deformation regimes initiated in Paleoproterozoic continue to Neoproterozoic. Paleoproterozoic ages and metamorphic conditions have similarity with those obtained in Ogooué Series (Gabon) and Transamazonian belt (NE Brazil), suggesting the correlation of the Nyong Series with the Ogooué metamorphic domain and the Transamazonian belt. The deformational structures are relevant to a part of a North-South collisional chain and open a debate about the Nyong Series’tectonic affinity. The regional significance of this study imply that the vast portions of Archaean materials have reworked under high-grade conditions during the Paleoproterozoic orogeny.