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(>52%),low-TiO_2(0.58)]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_2O_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 and0.33,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_2O_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 by25-30%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 mantle—and 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.
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