Unveiling the petrogenesis of alkaline silicate rocks at the Sevattur Carbonatite Complex, India

Abstract This study investigates the evolution of alkaline silicate rocks in the Southeast of the Sevattur Carbonatite Complex, intruding granite gneiss country rock. These rocks include monzodiorite, monzonite, syenite, albitite, and granite, alongside ultramafic enclaves known as pyroxene hornblendite. The present work unveils the intricate fractional crystallization processes within an alkali-rich basaltic magma system supported by mineralogical and geochemical studies. Mafic minerals such as diopside, pargasite, interstitial magnetite, and ilmenite indicate early cumulate textures forming at high temperatures. Amphibole and diopside alongside apatite inclusions suggest the presence of alkalis, fluorine, phosphorus and H2O in the primary magma. A coherent mineralogical and geochemical continuum from pyroxene hornblendite to monzodiorite, monzonite, and syenite with decreasing temperatures indicates fractional crystallization from a common primary magma. Furthermore, the absence of chilled margins and distinct boundaries dismisses a xenolithic origin for pyroxene hornblendite. The formation of granite, likely occurring during late-magmatic to hydrothermal stages, is characterized by K-feldspar, albite, and quartz, with clinozoisite and chlorite. Albitite occurrences as pegmatitic veins in syenite monzonite with shared geochemical traits with syenite and monzonite, suggesting a late-stage derivation from a common magma. Notably, these rocks lack the characteristic alkali-rich mineral assemblages, dispelling the notion of fenitization.