Conclusions
The field and the geochemical data suggest the presence of two volcanic rock associations in the Sonakhan greenstone belt: (1) an oceanic plateau association composed dominantly of tholeiite basalts and (2) a compositionally diverse intra-oceanic island arc association. The latter association is composed of tholeiite to andesite, dacite and rhyolite (BADR series). The REE patterns of the Sonakhan greenstone oceanic plateau basalts vary from depleted N-MORB like, to flat oceanic plateau like. Similar REE patterns have been reported from the Phanerozoic plume-derived oceanic plateaus and ocean islands (Kerr and Mahoney, 2007; Kerr, 2004; Hofmann, 2004). The presence of both the oceanic plateau and the island arc association in the Sonakhan greenstone belt can be explained by the initiation of a subduction zone at the edge of an oceanic plateau. Compositionally diverse lavas including basalts, andesite, dacite, rhyolite erupted from an island arc developed at the edge of the oceanic plateau. Extension of the overriding plate led to the rifting of the arc, resulting in the formation of an intra-arc basin for the deposition of the clastic rocks now represented by the Arjuni Formation. Thus, it is apparent that the plume-arc interaction model is a viable mechanism for the evolution of the continental crust during the Neoarchaean to Paleoproterozoic.