Singhbhum granitoid complex has been intruded by numerous mafic dykes trending in different directions. The studied dykes were originated from subalkaline magma, ranging in composition from basalt through basaltic-andesite to andesite. In the present work, the studied dykes are divided into two groups on the bases of abundance of SiO 2 , MgO, Al 2 O 3 , Ni, and Cr. The first one has higher Mg# than that of group II. These dykes have enriched incompatible trace element patterns. These are particularly enriched in the light rare earth elements and large ion lithophile elements with depleted high field strength elements (Nb, P, Ti). High Ba/Nb and Sr/P ratios of present mafic dykes are the indications of subduction signature. The geochemical characters of the back arc extension basalt tectonic setting is suggested for the studied dykes. Higher PM-normalized Th/Nb, Rb/Nb, and Ba/Nb ratios of studied samples support their non-plume source.

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The high-Mg mafic dykes from the Singhbhum Granitoid Complex in East India have geochemical characteristics [e.g., enrichment of the large ion lithophile elements and light rare earth elements (LREEs) relative to high field strength elements (HFSEs): high-MgO ([8 %), high-SiO 2 (C52 %), low-TiO 2 (B0.5 %), and high CaO/Al 2 O 3 (C0.58)] similar to those found in boninitic/noritic rocks. Their high percentage of orthopyroxene as a mafic mineral and of plagioclase as a felsic mineral, and normative hypersthene content greater than diopside content are also indications of their boninitic/noritic affinity. On a triangular diagram of MgO-CaO-Al 2 O 3 and on binary diagrams of Ti/V vs Ti/Sc and TiO 2 vs Zr, these samples show geochemical similarities with Phanerozoic boninites and Paleoproterozoic high-Mg norites. On major and trace element variation diagrams, these dykes show a normal crystallization trend and their Nb/La (\0.5) and Nb/Ce (\0.21) values lower than average bulk crust (0.69 and 0.33, respectively) suggest no crustal contamination. Their low values of Rb/Sr (0.11-0.41) and Rb/Ba (0.10-0.27) also suggest little or no effect of post magmatic processes. Their TiO 2 (0.27-0.50), Al 2 O 3 /TiO 2 (19.30-42.48), CaO/TiO 2 (12.96-32.52), and Ti/V (12-18) values indicate derivation from a depleted mantle source under oxidizing conditions such as a mantle wedge. Ni vs Zr modeling shows that the studied high-Mg dykes were generated by 25-30 % melting of a refractory mantle source. Enrichment of Rb, Th, U, Pb, Sr, and LREEs, and depletion of HFSEs-especially Nb, P, Ti, Zr-on primitive mantleand chondrite-normalized spider diagrams, respectively, are clear signals that the slab-derived component played an important role in the formation of melts for these rocks in a supra-subduction zone setting.