Abstract
The basic dykes in Mikir Hills have gabbroic composition. The prominent trends of these dykes are E-W in Southern part of Mikir Hills and NE-SW trend in the Northern Part of Mikir Hills. The geochemical characterization of dyke rock shows that they are subalkaline to alkaline basalt in nature, medium to high potassic, high titanium, Fe enriched tholeiites. The evolved nature of magma is represented by low Mg# 39.34 to 49.76 and are characterized by relatively low abundances of MgO, Cr, Ni, Zr, Y and high Rb, Ba, Th, Nb, indicating the within plate basalt (WPB) and continental rift basalt (CRB) chemical affinity. This dyke activity may be related to the extensional tectonics related to Proterozoic rifting hence, showing characteristics of continental rift basalt (CRB) type. The nine samples of gabbro define a five-point Rb-Sr isochron age of 1200±67 Ma with 87Sr/86Sr ratio of 0.70477±0.00042 with MSWD of 0.85. The Sm-Nd model ages (TDM) varies from 1600 to 2018Ma (eNd +0.11 to −2.04) indicates that the protolith from which these gabbroid rocks are derived is mostly Palaeo- to Meso-Proterozoic in age. The isotopic evolution of initial Sr, Nd and Pb reveals crustal contamination.
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