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Abstract
This paper presents the petrology and geochemistry of syenogranites that occur around Sitarampally area, NW of Narsapur in Medak district of Telangana within Eastern Dharwar Craton. Geologically, Sitarampally region is dominated by granitic rocks of Precambrian age.The lithological variants in the study area include granodiorite and monzogranite grading through syenogranite, granite to alkali feldspar granite-quartz syenites. The syenogranite is medium to coarse grained, inequigranular, porphyritic in texture and composed of K-feldspar (microcline perthite; 42-53% by volume), quartz (21-25%) and plagioclase (14-20%) in the order of decreasing abundance. Mafic minerals include amphibole (4-9%) and biotite (2-8 %) while the accessories are magnetite, titanite, calcite and apatite. Presence of discrete plagioclase grains in substantial proportions suggests sub-solvus conditions of crystallisation of the parental magma. The syenogranite has high SiO2 (70.77-73.86 wt. %), high K2O (6.11-7.11wt. %) and low Na2O (2.78- 3.40 wt.%). The rock is hypersthene-normative and calc-alkaline with low iron enrichment. The chondrite normalised REE patterns of syenogranite display LREE-enriched and HREE-depleted patterns with negative Eu anomaly. The syenogranites show high LREE/HREE ratio that hints at either fractional crystallisation or an LILE-enriched source. The negative Eu anomaly indicates the role of feldspar in the genesis of the syenogranites. The syenogranites of Sitarampally conspicuously display an Atype character and warrant detailed investigations.
Keywords: Geochemistry, Petrology, Syenogranite, A-type, Sitarampally, Eastern Dharwar Craton.
1. Introduction
Granitic rocks occupy a substantial portion of the continental areas particularly the Precambrian shields and also the Phanerozoic orogenic belts. These rocks also occur in other continents. Their abundance in oceanic setting is limited. Hence, the study of granitic rocks assumes greater significance in understanding continental growth through the geological past (Condie et al., 1985).Understandably, granites and related rocks have provided motivation to a large number of investigators since the beginning of this century, and systematic studies have been carried out on varied aspects of these rocks. Our perceptions and the present state of knowledge on multifaceted aspects of granitic rocks have their roots in the foundations, laid by pioneering work (Artherton, 1993) during the last couple of centuries.
Historical developments on the study of granitic rocks presented here are mainly based on publications of [Pitcher, 1997]. The later part of the 18th Century has provided a platform...