Chemical character of the Ngovayang gneisses in the northwestern border of the Congo craton (south Cameroon): sources and geotectonic framework

摘要: This article examines the results of chemical data granitoids Ngovayang massif at Northwestern border Congo craton in South Cameroon. The aim is to identify sources and geotectonic framework emplacement these formations. It a contribution understanding geodynamic context Nyong unit. 24 samples were analyzed by XRF ICP/MS are constituted orthogneiss, charnockitic gneiss, migmatites metagranites. study brings out progressive variation nature gneissic basement this massif. Orthogneisses principal rocks characterized an enrichment Na as opposed impoverishment K. confirms their plagioclase alkaline feldspar, K/Na ratios < 0.5. Trace element contents also characteristics, marked light rare earths (Laavg=10.48ppm) heavy (Ybavg=0.63ppm). Their spectra much fractionated ((La/Yb)N=15.86) without any significant anomaly Eu but negative Ti Nb. These confirm its belonging TTG type trondhjemitic affinity. have granodioritic composition calco-alkaline. They low Y content comparable with CA2 pluton. originate from melting source containing garnet residues, similar those generating TTGs. migmatitic gneisses seem be product sediments. Charnockitic two different trends; firsts procedure that differentiation seconds tonalitic formed partial no eventually hornblende. No matter domain, formations sector present variable manner, LILE (Rb, Th sometimes K). show metamorphites products archaean deformed during collision Sao Francisco cratonic blocks Eburnean orogeny.