Geochemistry of Late Proterozoic Sendra Granitoid Suite, Central Rajasthan, India : Role of Magma Mixing/Hybridization Process in their Genesis

Cluster analysis based on major elements demonstrates existence of granite, granodiorite and tonalites as distinct natural sub-population in the Sendra granitoid suite. The peraluminous granite with limited variation in mineralogy and chemistry is characterised by higher total iron, K₂O, mol. A/CNK, K₂O/Na₂O, Rb, Ba, Li and lower Sr as compared to the granodiorites and tonalites of the suite. Different trends for tonalites. granodiorites and granites in variation diagrams coupled with lower DI values of the granites in comparison to some of the tonalites and granodiorites, disallow interpretation of their relationship in terms of closed system equilibrium crystal fractionation or rcstite unmixing.

Principal component analysis of the data negates the possibility of the geochemical variations being controlled by a single process. The presence of mafic microgranular enclaves (MME) in the granodiorite and tonalite suggest mixing of the felsic and mafic magmas. The homogeneous nature of the granite and the absence of tonalitic and granodioritic components in the Chang pluton are due to emplacement of unadulterated granitic melt generated in the lower crustal region by basaltic underplating. The granodiorite and tonalite with variable chemical composition, represent subsequent mixing of granitic melt with the underplating basaltic magma and different degrees of thermal and chemical disequilibrium in the hybrid magma.