Mantle-crust-interaction and subduction dynamics in Central Cameroon: Evidence from the Pan-African Linté microgranular magmatic enclaves (MMEs) and host syenite

Abstract

The Central African Fold Belt (CAFB) in Cameroon is characterized by voluminous intrusive rocks hosting microgranular magmatic enclaves (MMEs) whose petrogenesis and tectonic implications remain unclear. Here, we present detailed geochronological and geochemical data of the host rocks and their MMEs from the Linté pluton in central Cameroon. The MMEs are finer-grained than their host syenite and both rocks are composed of alkali feldspar, plagioclase, biotite, amphibole and pyroxenes as main mineral phases. The enclaves show lower Mg#, total alkalis and transition elements contents, and are more HFSEs depleted than the host syenite. Both rocks are characterized by high-K, metaluminous I-type, alkaline to sub-alkaline and magnesian affinities. The Ti-in-zircon thermometer suggests crystallization temperatures of 615–1080 °C and 613–1008 °C for syenites and MMEs, respectively. Their zircon trace element distribution and patterns coupled with whole-rock geochemical features indicate that the Linté intrusive rocks were most likely originated from interaction of mantle-derived magma with crustal material. LA-ICP-MS UPb zircon analyses yield emplacement age of 599 ± 3 Ma and 597 ± 4 Ma for the host syenite and MMEs, respectively, indicating coeval crystallization date. Integrated whole rock geochemistry, UPb dating and Ti-in-zircon thermometry data indicate that the Linté syenite were probably formed from a mantle-derived ultrapotassic alkaline melt with significant crustal contribution, while MMEs are likely derived from a similar but separate melt with more fractionation and crustal contamination. The genesis of the host syenite and MMEs magmas started with break-off of the Congo plate after subduction and collision. This initiated an upwelling thermal pulse and underplating of mafic magma which led to partial melting of the Paleoproterozoic crust of the Central Cameroon.