Rutile U-Pb ages and implications for the extension of the timing of the Eburnean overprint in the Ntem Complex (southern Cameroon) portion of the Congo Craton

Abstract

To gain an understanding of the tectono-metamorphic evolution of the Congo Craton in the southern Cameroonian Ntem Complex, alluvial rutile EPMA geochemistry and LA-ICP-MS U-Pb geochronology were carried out, and for the first time, robust rutile ages are obtained in that section of the Congo Craton. Concentrations of Nb vary from 287 to 7074 ppm and those of Zr and Cr from 7 to 592 ppm, and from 75 to 5836 ppm, respectively. These data suggest Minto alluvial rutile was sourced from mainly metapelitic and accessorily metamafic rocks. The Zr-in-rutile thermometer indicates a range of temperatures between 430 and 720 °C, with an average temperature of 613 °C. This suggests that the alluvial rutile rock sources were formed under conditions of amphibolite facies metamorphism. Five alluvial rutile grains yield overlapping and concordant ages of 1974 ± 8.8 Ma, 1987 ± 13 Ma, 1992.2 ± 8.4 Ma, 1989.1 ± 8.3 Ma, 1985.1 ± 12.1 Ma, respectively. These results are all consistent with a single Paleoproterozoic metamorphic growth event. The rutile ages suggest that Minto, in the southern part of the Ntem Complex, was subjected to Eburnean thermal rejuvenation. Therefore, our findings extend the timing and location of the Eburnean overprint in the Cameroonian Congo Craton portion beyond the previously recognised spatiotemporal window.