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

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 degrees 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.