ECO-CHRONICLE 55 ECO-CHRONICLE, Vol. 5., No. 2. ISSN: 0973-4155 June, 2010, pp: 55 - 58 PETROGRAPHY OF ULTRAMAFIC ROCKS ALONG SIRUMUGAI AREA, COIMBATORE (DIST), TAMILNADU. Santhosh Kumar, E., Kumar, R.S., Prabhakaran, R. and Permcharles, A. Department of Earth sciences, Annamalai University, Annamalai Nagar, Tamil Nadu. Corresponding Author: [email protected] ABSTRACT The sirumugai Area is characterized by occurrence of ultramafic rocks aligned parallel to the Bhavani shear zone, intruding the Gabbroic -Anorthosite –Gabbroic-Pyroxenite suite. The ultramafic rocks occur as small lenses, pockets, veins, and thindykes and are intimately associated with mafic (Gabbros) rock. A few samples from the country rock were selected for the modal analysis. The characters represent that they might have been product of Archaean-Granodiorite-Tonalitic Gneisses and basic, ultra basic rocks are of which are predominant components of continental crust at the time of its formation. Key words: Petrology, Ultramafic, Sirumugai, Anorthosite. INTRODUCTION Analytical Techniques Ultramafic roués have received Chemical – mineralogical classification was considerable affection within the geological carried out using a CIPW norms thin community in recent years because they sections of gabbroic – anorthosite gabbroic provide excellent opportunities to gain – pyroxenite were studied using laborious insight into the in accessible realm of poles microscope and photo graphed on mantle rocks. Mostly they are formed by the leica micro system camera. partial melting of upper mantle and facilitate in the understating of the details of Geology of the Area fractionation origin, tectonic history and other petrological process (Raymond 2002) The study area lies between the east ultramafic roués act as hosts for Cr, Ni, Cu longitude 77 00 to 77 70 and the north and PGE mineralization. latitude of 11 24’ and 11 19’ of the SOI topo sheets (Fig 1). The area fails in the trichy The ultramafic rocks of sirumugai area Madurai plate. The suture zone are the gabbroic – anorthortes, gabbroic – mettupalayam-perambalur suture zone pyroxenites suite form the focus of (Gopalakrishana ,1990) the gabbroic interest. anorthosite – gabbroic – pyroxinite suite 56 ECO-CHRONICLE covers about 1/10 of the mapped area. The gabbroic, gabbroic – anorthosite Important out crops of this rock are found in are indicated to be tectonic slices with places near about thenkal malai and odhi in gneisses as their contacts are malai (Fig 2). invariably sheared (Jayananda et al, 1995). Fig.1. Location map of the study Area. The sathyamangalam supracrustal of the area include hornblende – biotite gneisses magnetite quartzite. The foliation trends which are variable from WNE–ESE. Ramakrishna (1991) proposes that the pandyan mobile belt, by analogy with the lim popo belt of South Africa. RESULTS AND DISCUSSION Petrography: Fig.2.Geology map of the study area. The ultramafic rocks of the study area are gabbro- anorthorite, gabbroic – pyroxinite studied under crossed nicols.The detailed petro graphic studies were carried our followed by model analysis for the selected this section of the representative samples. In thin section these rocks often show and equigranalar inter locking granolithic texture with medium grained. They are of labordorite composition. Wavy extinction, Fig-3. Shows AFM Diagram wedging and distortion of twin lamellae are common which indicate stress effects. It’s also common as islands with in garnet pyroxenes show higher degree of alteration. In some sections the rocks shows a highly cataclastic fabric. The petrochemical characters of these rocks reveal ECO-CHRONICLE 57 Fig. 4. Petrographic thin sections. 58 ECO-CHRONICLE that they are disintegration (or) early almandine-pyrope type which according to Archean grano-dioritic-tonalitic gneisses ramberg indicates formation under (Winkler, 1976). pressure environment. Geochemistry: REFERENCES The Chemical data Presented here and the Allegre Cj, Poirier Jp, Hhumier E, Hofmann discussions are follow (hollocher one if the Aw (1995). The chemical composition of the sampler form the country rock was selected earth planet. sci. lett. 134: 515-528. for modal ananlysis. The hornblende biotite gneisses shows higher silica in the range Ballhaus, C.G. & Glikson, A.Y., 1995, of 44.14, AL2O3-10.51, Fe2O3-11.28, Feo- Petrology of layered mafic-ultramafic 16.79, Mgo-12.89, Cao-16.34 and K2O-1.79 intrusions of the Giles Complex, western by the modal analysis.the character Musgrave Block, central Australia. AGSO represent that they might have been product Journal, 16/1&2: 69-90. of Archean grano-dioriteic-tonalitic gneisses. Which are predominant Blatt, Harvey; Tracy, Robert J.; Owens, Brent component of continental crust at the time (2005), Petrology: igneous, sedimentary, of the formation On AFM Diagram the and metamorphic (New York: W. H. samples plot in the field of metamorphic Freeman). ISBN 978-0716737438 peridotites and ultramafic rocks (Coleman, 1977). Radhakrishna, T.; Divakara Rao, V. and . Krishna Rao, J.S.R.(1982). Occurrence and CONCLUSION significance of awaruite in the Dras ultramafics, Kashmir Himalaya, India. In the sirumugai area small outcrops of Mineralogical Magazine, 46: 405-484. ultramafic rocks in association with gabbro- anorthosite-gabbro-pyroxinite. The suite of Sinharoy, S. & Radhakrishna, T. (1982). rocks include a dominant gabbroic facies Geochemistry of the ultramafic and mafic and relatively subordinate anorthositic rocks complex of Agali, Kerala and its and pyroxinites. It shows a distinct implications for Archaean greenstones of stratiform layering. The garnet form South India. Neues. Jah. Miner Abh., 143 : anorthosite rock is almandine grosular and 309-330. ECO-CHRONICLE 59 ECO-CHRONICLE, Vol. 5., No. 2. ISSN: 0973-4155 June, 2010, pp: 59 - 66 A MULTIVARIATE STATISTICALANALYSIS OF GROUNDWATER CHEMISTRY DATAIN CUMBUM VALLEY WATERSHED MADURAI DISTRICT TAMIL NADU, INDIA. Venkateswaran, S. and M. Vijay Prabhu Hydrogeological Laboratory, Dept. of Geology, Periyar University, Salem, Tamil Nadu. Corresponding author: [email protected] ABSTRACT The Cumbam valley watershed, located in Uttamapalyam and a small part of Periyakulam taluk, the western corner of Madurai District covers an area of about 890.97 Km 2, Tamilnadu, has been selected for this study. A multivariate statistical assessment has been adapted to the classification of a large, irregular dataset of 55 subsurface water samples in pre-monsoon 2009 and analyzed +2 +2 + + - - -2 for various water quality parameters such as pH, EC, TDS, Ca , Mg , Na , K , HCO3 , CO­3 , SO4 and Cl-. Hydrogeochemical data for 55 groundwater samples were subjected to Q- and R- mode factor and cluster analysis. R-mode analysis reveals the inter-relations among the variables studied and the Q-mode analysis reveals the inter-relations among the samples studied. The R-mode factor analysis shows that Mg and CI with CO3 account for most of the electrical conductivity, total dissolved solids and total hardness of the groundwater. Both Q-mode factor and Q-mode cluster analyses shows that there is an exchange between the river water and adjacent groundwater. Cluster classification map reveals that 97.79% of the study area comes under cluster I classification. Key words: Groundwater – Multivariate statistical analysis – Factor analysis, Cluster analysis INTRODUCTION types, topography of the area, human activities on the ground, etc. Apart from these The earth without water is difficult to factors, Charnockite, Calc-Gnieses, imagine. There is evidence that the life on granulites and contact between them play the earth originated in water. Today, water is an important role in determining the quality continuously polluted from different of the groundwater. sources. In the current world economic paradigms, sustainable socioeconomic In this study, such a situation has been development of every community depends deduced by using multivariate statistical much on the sustainability of the available techniques such as factor and cluster water resources. Water of adequate quantity analyses. Here, a qualitative study has been and quality is required to meet growing attempted to major cations and anions household, industrial and agricultural interaction in the groundwater. Multivariate needs. Sub-surface water quality is a very statistical analysis has been successfully sensitive issue, which transcends national applied in a number of hydrogeochemical boundaries. The quality of groundwater is studies. Steinhorst and Williams (1985) controlled by several factors, including used multivariate statistical analysis of climate, soil characteristics, manner of water chemistry data in two different field circulation of groundwater through the rock studies to identify groundwater sources. In 60 ECO-CHRONICLE their application of multivariate analysis to The area around Cumbum is diversified by chemical data, Usunoff and Guzma´n- several ranges of hills, falls and rapids which Guzma´n (1989) demonstrated the impart to the region a picturesque usefulness of the approach in appearance. The prominent mountain of the hydrogeochemical investigations when study area is the High Wavy Mountain and it considering the geological and is flanked on either side by hills. In the hydrogeological knowledge of the aquifer. eastern portion, there is an intermountane Multivariate statistical analyses, such as valley called the Varshanad valley. cluster and factor, aim to interpret the governing processes through data MATERIALS