Introduction
The Neoarchaean to Paleoproterozoic period is characterized by major crustal formation in the geological history of the Earth (Puchtel et al., 1999). The juvenile crusts formed during this period are preserved within many greenstone belts. Geochemical studies of these greenstone belts have revealed contrasting and diverse rock types (Puchtel et al., 1999; Sandeman et al., 2006; Van Boening and Nabelek, 2008; Polat, 2009 and reference therein) indicating diversity and complexity in the crust formation and evolutionary processes. In the last two decades, the island arc model has been the most popular mechanism describing the formation of the continental crust. But during the 1990s, based on strong geochemical database, the plume model was proposed for the origin and growth of many continental nuclei (Stein and Goldstein, 1996; Galer and Mezger, 1998). Mantle plumes generated large amount of basaltic melts rather rapidly in the oceans, and also on the continents, creating plateaus. The oceanic plateaus may accrete laterally to the continents producing new continental fragments (Abbott et al., 1997; Desrochers et al., 1993). Recent geochemical studies of many greenstone belts point to yet another model, the plume-arc accretion model, for the formation and evolution of the crust (Dostal and Muller, 2004; Polat et al., 2005; Polat and Hofmann, 2003, Dostal et al., 2004; Manikyamba et al., 2004; Polat, 2009). This model envisages that many Precambrian greenstone belts which were formed in an intra-oceanic environment show spatial and temporal co-existence of hotspot related and subduction related rocks. Although, apparently contradictory, this mechanism seems to have played an important role in the generation and evolution of Neoarchaean to Paleoproterozoic crust. Large amounts of geochemical data have been growing, especially over the last decade, in favour of this model.
In this contribution, we present major and trace element data, including rare earth elements of the Sonakhan greenstone belt of Bastar craton, central Indian shield, with a view to placing constraints on magma type(s) and source composition of the mafic and felsic volcanic rocks in the light of modern tectonomagmatic concepts. The geochemical data, in combination with field evidence, will be used to develop a comprehensive model for the Neoarchaean to Paleoproterozoic continental growth of the Indian shield.