REE- bearing Quartz Syenite from Purimetla Alkaline Complex, Cuddapah Intrusive Province, Peninsular India

The Purimetla alkaline pluton is one of the prominent nepheline syenite pluton among the several alkaline plutons emplaced along the contact of Eastern Dharwar and Eastern Ghat belt located at the eastern margin of the cuddapah intrusive province (CIP). The rift/suture between the Vinjamuru and Ongole domains of Krishna province, Eastern Ghats Belt (EGB) hosts this alkaline complex. In this pluton both alkaline (feldspathoidal) and sub alkaline (Non-feldspathoidal) rocks are co-spatially arranged. Detailed geochemical studies on the quartz syenite of Purimetla, indicate that these rocks are characterized by high alkali (9.35-12.05 wt%) especially K2O (7.12-8.8 Wt %) contents with metaluminous nature. Enriched in LILEs (Rb, Ba, and Sr) and depleted in HFSEs (Ta, Nb, Ti) along with pronounced Eu and TNT (Ta, Nb, Ti) negative anomalies are the distinguishing characteristics of these rocks. They also have high LREE contents and strong fractionation between LREEs (1826 ppm) and HREEs (92.7 ppm). Enriched LILE, LREE along with TNT negative anomalies reflect the partial melting, fractional crystallization followed by crustal contamination processes in the genesis of these syenites.