Olivine composition of calcite-carbonatite from Sevvattur carbonatite alkaline complex, Dharmapuri Rift Zone, Southern Granulite Terrain, India

Abstract

Olivine in carbonatites worldwide is mainly of Mg-rich composition (forsterite: Fo₈₅ and Fo₉₉). However, the occurrence of fayalite (Fo_<50) is extremely rare except few localities. The Sevvattur carbonatite alkaline complex (SCAC) is part of large Tirrupattur carbonatite-alkaline complex (TCAC), Southern India, which consists of early to late differentiated/fractionated products from dunite-wehrlite-shonkinite-carbonatite to ferrosyenite. In TCAC olivine composition shows decreasing Fo₉₃ to Fo₀₆ contents from early dunite to more evolved ferrosyenite. We report here an occurrence of low-Ni, olivine with intermediate Fo_60-65 content and low 100*Mn/Fe, Ni/Co, V/Sc ratios from the SCAC. Textural and compositional evidence reveals the xenocrystic (exotic) nature of olivine and possibly linked with multiple stages of crystal melt interaction in the protracted magmatic evolution and associated metasomatic processes during the interaction of peridotite lithosphere with carbonatite magma in the TCAC at low temperature and shallow depth. It is concluded that the olivine in the Sevvattur Carbonatite Olivine provide the missing link or compositional gap during the evolution of the TCAC of early to late differentiated products from dunite (Fo_90-91)-wehrlite (Fo_70-72)-shonkinite (Fo_72-77)-carbonatite (Fo_{∼90 and 63–65} present study) to ferrosyenite (Fo_03-06).