The Samapleu mafic–ultramafic intrusion (western Ivory Coast): cumulate of a high-Mg basaltic magma with (coeval) ultrahigh-temperature–medium-pressure metamorphism

Abstract

Mineralogical, geochemical and metamorphic characterization of the Samapleu intrusion shows that it is composed of cumulates of mafic and ultramafic rocks. The ultramafic unit resulted from a single and progressively evolved primitive magma. The mafic unit could have evolved from the same magma or could have formed following a second, more evolved magma injection. The data and signature of major, trace elements and rare earth elements of the mafic intrusion indicate that it is of basaltic composition with a low Ti and high content of MgO. In addition, it is formed by fractional crystallization under the impingement of a mantle plume at the base of the continental crust, inducing textural and mineralogical characteristics of high metamorphic grade with a low level of contamination. Contact metamorphism is represented by hybrid lithofacies composed of mixtures of mafic igneous and aluminous semipelitic rocks with ultrahigh temperature (T = 850 ± 100°C and P = 7.5 ± 1 kbar), which confirm the establishment of this intrusion at the base of the continental crust (c. 22 km). Therefore, the Paleoproterozoic age (2.09 Ga, age U–Pb on rutile) of the Samapleu intrusion would imply that the intrusion could be coeval with the plume-related ocean flood basalts of the Birimian sequence.