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.

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.

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

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 6 75.347 0.103 13.588 0.012 1.294 1.138 0.21 3.761 4.389 0.029 99.871 7 74.718 0.222 13.47 0.042 2.287 2.051 0.669 4.724 1.29 0.029 99.502 8 48.876 3.098 16.502 0.608 10.57 0.534 9.241 0.494 9.605 0.025 99.553 9 75.361 0.101 13.63 0.012 1.276 1.112 0.194 3.792 4.345 0.03 99.853 10 75.489 0.049 13.987 0.01 0.47 0.847 0.06 3.573 5.349 0.021 99.855 11 76.118 0.105 13.341 0.019 0.953 1.028 0.197 3.255 4.759 0.026 99.801 12 73.241 0.068 15.548 0.04 0.86 0.748 0.133 3.924 5.208 0.029 99.799 13 77.198 0.081 13.547 0.016 0.826 3.089 0.165 4.492 0.424 0.025 99.863 14 73.4 0.251 13.686 0.024 2.282 1.536 0.287 2.679 5.566 0.057 99.768 15 73.752 0.266 12.961 0.033 2.466 0.557 0.573 2.15 6.985 0.03 99.773 16 76.901 0.119 13.322 0.075 1.431 1.472 0.217 3.965 2.326 0.028 99.856 17 69.821 0.74 9.343 0.084 6.137 4.961 4.813 0.86 2.058 0.106 98.923 18 73.894 0.058 14.208 0.186 1.219 0.501 0.087 3.25 6.341 0.025 99.769 19 70.089 0.737 9.319 0.084 6.121 4.944 4.808 0.863 2.046 0.107 99.118 20 76.806 0.113 13.47 0.074 1.373 1.461 0.206 3.993 2.356 0.026 99.878 Average 72.20 0.36 13.86 0.07 2.45 1.59 1.15 3.01 4.91 0.05 99.65

GEOCHRONOLOGY OF THE MIGMATITES IN STUDY AREA:

The southern granulite terrain rocks Archean to Proterozoic formations. The metamorphism on the basis of Sm–Nd and Rb–Sr isotope studies. On the rocks of Madurai Block, Jayananda and Peucat (1995) have reported Pb evaporation ages.

Maharani,K., Chidambaram,S. and Rajendran,S.

A B

C D

E F

G34 H

THE STUDY OF MAJOR ELEMENT GEOCHEMISTRY OF MIGMATITES IN AND AROUND MELUR REGION, MADURAI DISTRICT, TAMIL NADU, INDIA

I J

Alkaline

Sub Alkaline

K L

Fig.6- Variation Plots for SiO2 vs all oxides, Sr/TiO2, P2O5/feo+mno+mgo, TiO2/feo+mno+mgo, Al2O3/Na2O+K2O.

GEOCHEMISTRY OF THE STUDY AREA:

The different rock samples collected from the study area and 20 samples selected for major elements analyses by Centre for Earth Science Studies, Thiruvananthapuum. Major element distribution reflects the mineralogy of the studied samples. The observation of overall analysed Data the samples higher SiO2, rather similar Na2O, slightly lower K2 O and CaO and clearly lower FeO,Mno,MgO and TiO2 contents than the associated Leucosome and melanosomes (Figs.6 A-F). Plots of the FeO+MgO+MnO/P2O5 Low concentration in P2o5 and increase in feo, Mgo & Mno (Figs.6). The plot Tio2 vs FeO+MgO+MnO denotes the very low concentration in tio2 and Feo, Mgo, Mno only one sample is very high Fig.6(h). It may be indicates the igneous origin that only one sample is metamorphic origin.The lower silica magmas are also lower in viscosity, so they may have experienced more crystal-liquid fractionation than higher silica magmas. This could very well be contributing to some of the scatter at low SiO2 (Rollinson (1993).

Maharani,K., Chidambaram,S. and Rajendran,S.

Fig.7. Variation Plots for Na2o vs K2o and K2o vs Mgo.

Fig-8

The Plotting of K2O/Na2O (Fig.7) shows slightly lower K2O content of the all sample and only one sample high concentration. It is due to leucosomes than the mesosomes

THE STUDY OF MAJOR ELEMENT GEOCHEMISTRY OF MIGMATITES IN AND AROUND MELUR REGION, MADURAI DISTRICT, TAMIL NADU, INDIA

(Omosanya,, mainly due to the absence of biotite and the low amounts of K-feldspars in the former. The leucosomes and mesosomes bands exhibit a rather similar range of Na2O suggesting either a similar proportion of plagioclase or a rather limited variation in plagioclase composition of the two bands.

Fig.7 Plot of MgO vs K2O for the Melur migmatite diatexites, showing the compositional field (rounded area) of the nearby mica gneisses and mica schists (Hannu Mäkitie, 2001).The biotite, garnet, orthopyroxene, plagioclase and quartz are also shown. The approximate location of melt compositions from melting experiments of pelitic rocks is shown as MELT (after Patiño Douse & Harris 1998, and references there in). (a) The SiO2–K2O diagram, all the samples falls in the field of Subalkaline and only one sample fall in the alkaline Region Fig.6 (L). (b) The rock are continental and passive margin igneous and metamorphic rocks on the plot of K2O+MgO vs SiO2 (Bhatia, 1983) (b) (c) All the sample falls in the field of S-type granites, even the metamorphosed gneisses on the SiO2–A/CNK diagram, where A/CNK = molar Al2O3/ (CaO + Na2O+K2O), aluminium saturation index (ASI). (c) (d) The rock are peraluminous on the A/CNK–A/NK diagram where A/NK = molar Al2O3/(Na2O+K2O), corroborating the low corundum content of (table.2,).

The aluminum saturation index (ASI: molar Al2O3/ (CaO + Na2O+K2O)) (Zen, 1986) was used to distinguish between S- and I-type granites (Chappell, 1999). On the A/NK– A/CNK diagram (Fig.6 I), all the samples plotted in the peraluminous field (A/CNK >1). The SiO2–A/CNK diagram (Clarke, 1992) shows that the samples are S-type granite with A/CNK >1.1 (Fig.6 , Omosanya, K).

Fig.9- (A & B) AFM Diagram and Field diagram for migmatites in study area.The AFM Diagram indicates all the samples are fall into the calc-alkaline series. One or two samples are the very low concentration in the sodium and Potassium (Fig.8 A&B ).

DISCUSSION:

Temperature range of granulite metamorphism suggests the necessity of a thermal anomaly for their formation rather than ambient conditions of the Precambrian lower crust (Fountain, M.H. Salisbury, 1981). Neoproterozoic magmatism also occurred throughout the

Maharani,K., Chidambaram,S. and Rajendran,S. southern parts of both the Western and Eastern Dharwar blocks, and is represented by granites, alkaline dykes and other thermal imprints.

CONCLUSION:

Generally the Migmatites are the mostly in igneous origin, and most of the samples fall into the igneous field, one or two samples are fall into the metamorphic because of the only one sample having the high concentration of Mg. The overall view the samples higher SiO2, rather similar Na2O, slightly lower K2 O and CaO and clearly lower FeO,Mno,MgO and TiO2 contents than the associated Leucosome and melanosomes. Plots of the FeO+MgO+MnO/P2O5 Low concentration in P2o5 and increase in feo, Mgo & Mno. The plot Tio2 vs FeO+MgO+MnO denotes the very low concentration in tio2 and Feo, Mgo, Mno only one sample is very high. Plot of MgO vs K2O for the Melur migmatite diatexites, showing the compositional field (rounded area) of the nearby mica gneisses and micaschists (Hannu Mäkitie, 2001).The plot Sio2 vs Na2O+K2O Indicates the most of the samples in study area fall in the Intermediate to Acid Igneous Rocks Only One Sample is fall in Ultrabasic rock. These inferences from the oxide-oxide plot. The biotite, garnet, orthopyroxene, plagioclase and quartz are also shown. The approximate location of melt compositions from melting experiments of pelitic rocks is shown as MELT.

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