A lithospheric mantle source for the Proterozoic kimberlites and lamproites from the eastern Dharwar craton, India: evidence from rare earth element inversion modelling

Abstract

Inversion of rare earth element (REE) concentrations of a Proterozoic kimberlite (Maddur) and lamproite (Ramannapeta) from the eastern Dharwar craton, India is carried out to discover the partial melt distribution with depth that could have been responsible for producing their REE distribution patterns. In order to reproduce the observed REE patterns, the source regions of these rocks need to undergo an extensive initial depletion event (similar to 20%) in the garnet stability field before being subjected to metasomatic enrichment and subsequent partial melting. The extensive initial depletion, probably represented by 'komatiitic type' melt extraction during the Archaean, necessitates the partial melting of the eastern Dharwar craton kimberlite and lamproite source regions to have taken place in lithospheric, but not convecting, mantle. This study rules out a 'transition zone' source recently invoked for such rock types from eastern Dharwar craton and elsewhere and therefore imposes important constraints as to the source regions of kimberlites and lamproites.