Hornblende bearing quartz syenite from the Proterozoic Podili alkali granite pluton, Eastern Dharwar Craton, India

摘要

The hornblende bearing quartz syenite from Podili alkali granite pluton located in the northern part of the Archaean Nellore schist belt (NSB) in the Eastern Dharwar Craton, SE India is presented in this paper. The hornblende bearing quartz syenite occurs as NNE-SSW trending elliptical body along the foothills of the host alkali granite in the northern part of the Podili pluton. Riebeckite bearing alkali granite, arfvedsonite-astrophyllite alkali granite and form part of the Podili alkaline granite pluton. Enclaves of metavolcanics of NSB are noticed in the Podili pluton. The hornblende bearing quartz syenite is coarse-grained, mesocratic, undeformed and exhibits sharp contact with the host Podili alkali granite. Petrographically the syenite exhibits hypidiomorphic texture and essentially composed of K-feldspar and hornblende with sub-ordinate biotite and plagioclase. Zircon, allanite, titanite, apatite, fluorite and ilmenite are the accessory phases. Plagioclase is also seen as euhedral inclusions and exsolved lamellae with the microcline microperthite. EPMA analyses revealed that the amphibole is hastingsite hornblende. The Podili syenite is characterised by lower SiO_2 content ranging from 53.64 to 58.68% and relatively higher Fe_2O_3 content ranging from 7.99 to 9.19%. The Fe* ranging in the hornblende from 0.96 to 0.98 indicating ferroan nature. Geochemical studies indicate that the syenite is metaluminous and exhibit calc-alkaline trend. The paper presents the succinct details on petrography, mineral chemistry and geochemical aspects of the hornblende bearing quartz syenite in Podili alkali granite pluton that falls within the zone of Proterozoic ferroan feldspathic magmatism demarcated to the east of Nallamalai Fold Belt, Eastern Dharwar Craton, SE India.