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Abstract
The Archean granite-greenstone terrane exposed around Atkur-Guntipally and Madanapally area in Mahabubnagar District of Telangana is comprised of granitoids of Peninsular Gneissic Complex (PGC) and 2.7 Ga metavolcanics belonging to Gadwal schist belt, in Eastern Dharwar Craton (EDC). The granite-greenstone sequence of the study area is located around the northern part of Neoarchean Gadwal schist belt. The present study pertains to the coarse grained, mesocratic granitic rocks that occur on either side of narrow N-S trending metabasalt (0.8 to 1.6 km width) in the area. Petrographically the granitoids exhibit hypidiomorphic texture and are essentially composed of K-feldspar, quartz, plagioclase, biotite + hornblende and zircon, epidote, apatite and opaques are noticed as accessory minerals. Mafic rich microgranitoid enclaves (MME's) are widely noticed indicating magma mingiling phenomenon. These granitic rocks are peraluminous in nature and exhibit a cal-alkaline trend. Major oxide geochemistry indicates high SiO2 (71.22 to 72-84%) and high Na2O +K2O (8.19 to 9.0%) content. Positive correlation between SiO2 vs alkalis (Na2o, K2O) and alumina (Al2O3) indicate normal differentiation trend characteristic of calc-alkaline plutonic felsic magmatism. Chondrite normalised REE plot of these granitoids exhibits conspicuous LREE enrichment, negative Eu anomaly and depleted HREE patterns indicating a crustal source.
Keywords: Peninsulr Gneissic Complex, Granites, Gadwal, Mylonite, Eastern Dharwar Craton.
1.Introduction
Granite magamtism has played a significant role in the growth and stabilization of the continental crust during Precambrian time, while the major phase of continental crust evolution in the Indian shield appears to have started around the middle-Archean and got completed by early-Proterozoic (Jayananda et. al. 2000, 2009, Divakara Rao et.al. 1999), wherein a number ofpulses of granite magmatism has been recorded and well documented partially in the Dharwar Craton of Peninsular India. The Late Archean- Proterozoic transition particularly associated with the schist belts of Eastern Dharwar craton (Prabhakar et.al 2009, Naqvi and Rogers, 1987; Radhakrishna, 1989) was witness to extensive granite magmatism and growth of continental crust. Granites exposed around Gadwal schist belt are generally referred to as 'unclassified' peninsular gneissic complex ( Perraju and Natarajan,1977). Subsequent mapping by Gopal Reddy and Rao, (1998) has lead to identification of various suites of granitoids within the Peniesular gneissic complex in the...