Archean crustal generation and Neoproterozoic partial melting in the Ivindo basement, NW Congo craton, Republic of Congo: Petrology, geochemistry and zircon U–Pb geochronology constraints

Abstract

We present systematic petrographic descriptions, geochemical and geochronological data from Souanké, Bomalinga, Elogo and Zoula areas in the Ivindo basement to understand the evolution of NW Congo Craton, Republic of Congo. Hornblende tonalite, biotite granodiorite, usually with hornblende-bearing enclaves, and granitic leucosome veins are ubiquitous in all areas. Specifically, coarse-grained muscovite-garnet-bearing pegmatite cross-cutting ancient mafic tonalite and felsic granodiorite in the Souanké area. Overall, three well-defined chemical patterns are described: (1) low SiO2 (57–63 wt%), high MgO + FeO (9–19 wt%) and metaluminous composition with intermediate LREE/HREE ratios and slightly positive Eu anomaly for tonalite, (2) middle SiO2 (67–73 wt%), MgO + FeO (7–1.5 wt%) and peraluminous composition with intermediate LREE/HREE ratios for granodiorite and (3) high SiO2 (72–75 wt%), low MgO + FeO (∼<1 wt%) and peraluminous character with low LREE/HREE ratios (flat patterns) and negative Eu anomaly in granitic veins and pegmatites. Regardless of the study area, the hornblende tonalites present similar ages (2884 ± 2.7, 2875 ± 5.6 and 2888 ± 3.2 Ma) that are near coeval with the ages presented by biotite granodiorites (2896 ± 8.9, 2880 ± 5.9 and 2875 ± 6.4 Ma), while granitic leucosomes have slightly younger ages (2850 ± 7.3, 2870 ± 8.2 and 2858 ± 7.2 Ma). Lastly, garnet-bearing pegmatite presents a Neoproterozoic/Cambrian transition age of 540 ± 1.6 Ma. Different enrichment LREE/HREE ratios combined with negative Nb–Ta and Ti anomalies may suggest a subduction-like setting for the generation of near coeval Mesoarchean tonalite-granodioritic crust. Whereas field relationships and flat REE patterns in the muscovite-garnet-bearing pegmatite indicate a younger ∼540 Ma crustal melting in the NW Congo Craton likely related to West Gondwana assembly. Further, these results confirm that the ∼2.9 Ga represents a significant period of continental reoworking within a magmatic arc setting.