Archean inheritances in the pyroxene-amphibole-bearing gneiss of the Méiganga area (Central North Cameroon): Geochemical and ²⁰⁷Pb/²⁰⁶Pb age imprints

The Méiganga area is located in the central part of the Panafrican belt of Cameroon. This region is underlain by a granitic and gneissic basement, crosscut, and covered by basaltic and phonolitic rocks. To the southwest of Méiganga, the pyroxene-and-amphibole-bearing gneiss shows the geochemical characteristics of Archean TTG (tonalite-trondhjemite-granodiorite) associations. The studied samples show LREE enrichment relative to the HREE (LaN/YbN = 7-28). This pattern of the REE, particularly the concentration of Y and Yb allowed us to consider some samples as derived from an Archean crust. Cathodoluminescence pictures of zircon crystals from the gneiss reveal magmatic oscillatory zoning with inherited cores. Age determinations employing the 207Pb/206Pb single-zircon evaporation method yielded Late Archean (∼2.6 Ga) to Palaeoproterozoic (∼1.7 Ga) ages. Ages around 2.0 Ga are interpreted to be close to the crystallization age, while the older ages might represent mixing ages, i.e., mixtures between a Palaeoproterozoic magmatic domain and an inherited Archean core. This study discusses the imprints of Archean crust inheritances on the pyroxene-amphibole-bearing gneisses of the Méiganga area. © 2008 Académie des sciences.