The Study of Major Element Geochemistry of Migmatites in and Around Melur Region, Madurai District, Tamil Nadu, India
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Bulletin of Pure and Applied Sciences Vol.35F-Geology (No.1-2)2016:P.29-38 Print version ISSN 0970 4639 Online version ISSN 2320 3234 DOI 10.5958/2320-3234.2016.00003.2 THE STUDY OF MAJOR ELEMENT GEOCHEMISTRY OF MIGMATITES IN AND AROUND MELUR REGION, MADURAI DISTRICT, TAMIL NADU, INDIA Maharani.K1, Chidambaram.S2, and Rajendran.S3 1Guest Lecturer, Alagappa Govt Arts College, Karaikudi 2Professor and Head, Department of Earth Sciences, Annamalai University. 3Assistant Professor, Department of Earth Sciences, Sultan Qaboos University, Sultanate of Oman Recieved 20 June 2016 : Accepted 24 November 2016 ABSTRACT The study investigating the exposed Archean lower continental crust of the Southern Granulite Terrain, India, shield important constraints on the nature and evolution of the deep crust, including the formation and exhumation of Granulites. The source for the high temperature granulite metamorphism for the southern granulite terrain may be attributed to high temperature carbonatite and alkaline intrusives in an extensional setting which followed an initial crustal thickening. The Southern Granulite Terrain (SGT) in India is one of the largest exposed Precambrian deep continental crustal sections in the world consisting of multiply deformed Archean and Neoproterozoic high grade metamorphic and magmatic rock. The Archaean and Proterozoic terrains of South India, some of the granitic intrusions contain xenocrysts which resemble the porphyroblasts of nearby migmatites. Migmatites with evidence for low pressure metamorphism and partial melting occur in the melur region. Although migmatitic rocks of the region are located near the granitic intrusions, the degree of partial melting is not related to intrusions and is irregular. It appears that partial melting and migmatization pre-date the intrusion of major granitic bodies in the region. Leucosomes in stromatic migmatites are commonly parallel to bedding planes and are mostly formed by metamorphic segregation and/ or in situ partial melting (showing mafic enclaves, pinch and swell structures). The melt fraction and migmatite type depend on the chemical composition of parent rocks and the distribution of high strain zones. Keywords: Tectonism, SGT, Migmatite, Geochemistry, Melur, Major Elements. INTRODUCTION Granulite terrains are also found in many Proterozoic and Phanerozoic collisional belts such as the Aravalli–Delhi fold belt and the Eastern Ghats Mobile Belt (India), the Grenville Front Tectonic Zone (USA), the Alps of Europe, and the Himalayas of Asia. The SGT is one of the most extensive Archean high-grade granulite terrains of the world, having an area of several thousands of kilometers. The Madurai Granulite Block are sometimes migmatitic gneisses, garnet-biotite gneisses or simply biotite gneisses. Major felsic/alkaline intrusive bodies of Munnar granite, Pariyaram granite (central MGB)The exposed granulites of the SGT act as a window, providing a unique opportunity to understand the nature of lower continental crust (Vijaya Rao, 2006). Maharani,K., Chidambaram,S. and Rajendran,S. The present study is focused on understanding the basics of migmatite rock types structure, major element geochemistry migmatite rocks in and around the melur region, Madurai district and tectonism of the Southern Granulite Terrain of India, located south of the low metamorphic grade Dharwar craton. EARLIER STUDIES The tectonic framework of south Indian shield region (SISR) has been studied by various geological and geophysical methods and reviewed by various workers (e.g., Drury and Holt, 1980;Drury et al., 1984; Radhakrishna, 1989; Chetty, 1996; Ramakrishnan,2003; Santosh et al., 2003, 2005, and the references therein). These tectonic studies have identified major shear zones within the SISR, namely, the Palghat–Cauvery shear zone (PCSZ), Moyar shear zone (MSZ), Bhavani shear zone (BSZ), Moyar–Bhavani shear zone (MBSZ), Mettur shear zone (MTSZ), and Achankovil shear zone (ASZ) Grady (1971) was the first to have pointed out the existence of several deep faults in southern India. The significance of shear zones in the tectonic history of granulite terrain was brought to light by Drury and Holt (1980) and Chetty, 1995 (Fig.1). Fig.1- Distribution of quartzite, calc-silicate gneiss, mafic granulite and meta-ultramafic rocks in the SGT (Joy Gopal Ghosh, 2004). The Transect extended across the southern part of the Archean Dharwar craton, traversing shear zones, alkali complexes, charnockite, and various gneisses of the region. 30 THE STUDY OF MAJOR ELEMENT GEOCHEMISTRY OF MIGMATITES IN AND AROUND MELUR REGION, MADURAI DISTRICT, TAMIL NADU, INDIA Seismic reflection data were reprocessed along two profiles in Tamil Nadu. P–T conditions of the metamorphic rocks provide useful constraints in formulating an appropriate tectonic model for high-grade granulite terrain. STUDY AREA The present study area falls in the Madurai district, melur region of southern granulite terrain and its survey of India Topographic sheet number 58 J/8. It covers the Latitude from 10º00’ to 10º10’ Longitude 78º14’ to 78º23’ (Fig.3). The study area is located in the NW of Madurai district, mostly undulated terrain of Boulders. Some of the reserve forests present in the study area are namely, Perumal malai Reserve forest, Alagar Hills Reserve forest. The major canal and channel is periyar main channel is crossing the study area. Here the major channel flowing accrossing the study area. The Roads are connected with the melur town to Locations of the study area. The present study area covers a part of Madurai block that lies between Palghat–Cauvery shear zone (PCSZ) in the north and Achankovil shear zone (AKSZ) in the south (figure.2). Fig.2 Geological Map of Southern peninsular India, Major Shear zones. The thick line popularly known as Fermor line (Fermor, 1936) delimits the northern boundary for charnockites. (Souce: John Kurian, 2000) Some workers believe that the SGT and the Eastern Ghats may be continuations of the Dharwar Craton in the south and the east, respectively (Ashwal, 2002). Figure. 1 is the tectonism, Structure and rock types and geological Age. 31 Maharani,K., Chidambaram,S. and Rajendran,S. GEOLOGY OF STUDY AREA: The study area having two different granitic formations, migmatite Gneiss and Quartzite formation of the study area is Azhagar hill, Perumal malai. Tectonic trends have been interpreted on the basis of alignment of these layered lithological bodies and field measurement of penetrative structural fabrics in various rocks types. The Gneissic formation is generally weathered very coarse to medium grained rocks. The mica bandings are more in the formations. The phenocrysts of Feldspars are present in the outcrop. The Garnets are also fine to big crystals in older gneissic formation. The dominant rock type exposed in this is charnockite, associated with khondalite. (garnet-biotite-sillimanite gneiss ± graphite), garnet-cordierite gneiss, migmatitic granitic gneiss, garnetiferous quartzo-feldspathic gneiss, calc granulite and quartzite. Thin bands (1 to 30 cm thick) of mafic granulite occur as enclaves in these rock types. Granites and thin veins of pegmatite and quartz intruded these rocks. The migmatised gneiss (Fissile Hornblende Biotite Gneiss) is weathered and very fresh in nature and the coarse grained texture. The migmatised gneiss is very coarse to medium grained and the intruded granite is very fine to medium grained in nature. The pegmatite is having very coarse to coarse grained texture. The grains are very less compactness. The field observation the formations are some of the later mineralisation patches of garnets and micas depending upon the temperature during the crystallization. Fig.3- Sampling Locations and Geology map of the study area 32 THE STUDY OF MAJOR ELEMENT GEOCHEMISTRY OF MIGMATITES IN AND AROUND MELUR REGION, MADURAI DISTRICT, TAMIL NADU, INDIA STRUCTURAL STUDIES OF MIGMATITES IN STUDY AREA The study area having the several structural features are observed in the outcrop number of Folds and Faults and joints are Present in the older gneissic rock (Fig.1). Meißner et al (2002) have suggested that the rocks of Moyar, Bhavani and Palghat Shear Zones have been affected by Neoproterozoic ( 600-490 Ma). INTRUSIONS ON THE MIGMATITES IN STUDY AREA The different intrusions are two types in the study area, such as pegmatite and Granite. The granitic formations are Grey granite and Pink Granite emplacement. Granite body Occurs as intrusion within the older gneiss and the earlier formation the commercial product of the pink granite is formed. In field observation some places the pegmatite body is intruded few feet wit in the older gneiss. The intrusion of gray granite is fine grained in nature. The nature of the formation is very fresh. The older gneissic formation having sheet joint and some minor quartz veins are also present. The observation of my study area having the formation is very fine to coarse grained in nature. These intrusions are having big crystals of Mica and Garnets (Yakymchuk, 2013). Table 1. Geochemical results of Major oxides in samples analyzed in the study area. S.No. SiO2 TiO2 Al2O3 Mno Fe2O3 CaO MgO Na2O K2O P2O5 Total 1 73.375 0.237 13.67 0.046 2.343 1.732 0.232 2.328 5.755 0.055 99.773 2 74.654 0.049 13.736 0.01 0.473 0.829 0.055 3.512 5.368 0.023 98.709 3 67.231 0.014 18.304 0.005 0.534 0.293 0.026 3.134 10.242 0.018 99.801 4 67.811 0.098 17.963 0.016 1.004 0.359 0.277 3.327 8.871 0.028 99.754 5 69.955 0.7 13.538 0.048 5.004 2.593 0.588 2.169 4.942 0.203 99.74