International Journal of Basic and Applied Sciences Prakash et. al., Vo. 1 No. 1 ISSN: 2277-1921 International Journal of Basic and Applied Sciences Vol.1 No.1. 2012 . 61-67 ©Copyright by CRDEEP. All Rights Reserved Full Length Research Paper Tectonic significance of the area west of Kodaikanal (South India): Applying Remote Sensing and GIS techniques D. Prakash*, C. K. Singh, U. K. Shukla, P. Chandra Singh and Deepak Center of Advanced Study in Geology, Banaras Hindu University, Varanasi 221 005 India *Corresponding Author: D. Prakash; E- Mail: [email protected] ABSTRACT Kodaikanal area resting over the Precambrian carton is characterized by a complicated structural pattern signified by a number of major regional scale and minor shear planes of local significance. These lineaments show all the evidences of geologically past and Quaternary tectonics that have greatly affected the geomorphological evolution of the area. Present study based on Digital Terrain Model (DTM), remote sensing, structural fabric supported by ground thruthing has revealed presence of two major lineament trends aligned in ENE-WSW and WNW-ESE directions and seems have developed in response to two major tectonic episodes in the area. Crosscutting relationship of these two trends suggests that ENE-WSW is older than the WNWESE which has been off stetted by the former one. Drainage pattern and the nature of escarps also point to a possible Quaternary reactivation of these two shear trends implying neotectonic activity in the area. Key Words: DTM, Kodaikanal, Remote Sensing, Tectonics, INTRODUCTION southern part of the Indian peninsula (Vaidyanathan The Kodaikanal massif encompasses the Annamalai, 1967; Vemban et al. 1977; Ramasamy et al. 1987; Palani and Cardamom Hills and is the largest upland Ramakrishnan, 1988; Ramasamy, 1989; Narsimhan, block (rising to 2800 meters) of granulites of South 1990; Kumanan 2001 among others). India (Fig.1a, b). In the western part of this massif (Annamalai hills), charnockites are extensively The present study is an attempt to evolve tectonic retrogressed. In Kodaikanal area, massive and implications deduced from the analysis of Digital homogenous charnockites are in sub-vertical contact Terrain Model, satellite remote sensing data with with a thick sequence of metasediments, the contact ground truthing in combination with field work. For zone coinciding with the eastern margin of the upland this purpose an area of 120 sq. km. west of massif (Prakash, 1999). At the contact zone, Kodaikanal (Tamil Nadu) has been selected. The cordierite-garnet-spinel-sillimanite migmatites study area (77°20΄00˝ to 77°29΄15˝ and 10°15΄00˝ to represent metapelites, but further east garnet- 10°21΄15˝) is situated 125 km NW of Madurai in sillimanite-biotite gneisses (Khondalite) predominate Tamil Nadu (Fig. 1c). The area is accessible by bus/ and are interlayered with calc-silicate rocks, train from Chennai via Madurai or Kodaikanal road quartzites, pelitic schists and conformable mafic- railway station. Frequent bus service on Kodaikanal- ultramafic layers (Prakash et al., 2007). Numerous Palani road and good logistics at Kodaikanal make screens of charnockite are interlayered with field works pleasant and easy. metasediments (Harris et al., 1982; Prakash et al., 2006, 2010; Prakash, 2010). TOPOGRAPHY Kodaikanal Plateau corresponds to the “Upper Studies carried out in the Peninsular India during last Palani”. The western or the Upper Palani from at the 3-4 decades have shown indications of possible top a plateau of around 170 sq. km. areas with an recent plate movements. These studies indicate average elevation of 2,500 meters above the mean sea evidences for Quarternary earth movements in the level. These comprises the three valley namely 61 Online version available at: www.crdeep.org International Journal of Basic and Applied Sciences Prakash et. al., Vo. 1 No. 1 ISSN: 2277-1921 Figure 1. a). Reference map of India. b). Structural patterns for Southern Granulite Terrain (after Drury et al., 1984) c). Geological map of the study area (Modified after Prakash, 2010). Parappar-Devaikarai Valley, the Gundar valley and spot height point map (Fig. 2). This DTM is useful the Upper Amaravathi Valley with several tool to interpret the geomorphic and tectonic features intervening peaks as- Perumal Hills (2,190 m), of any area in conjunction with satellite data and Obeservatory Hills (2,305m), Karumarkadu Hills, ground truthing. The digitized drainage map was Vembali Hills and Vandaravu Hills. Kodaikanal lies prepared under GIS software. Ordering of drainages on the southern edge of Vembali hill. The Upper has been done on the basis of Horton (1945) (Fig. 2). Palani consists largely of plateaus of rolling down A precise lineament pattern was prepared from the covered with coarse grasses and isolated sheltered raw and the digitally processed IRS Landsat7-ETM+, woods, hidden from general view. Theses shoals are dated - 2006-11-23, Path Row 141/48 data on the well watered and form the higher ranges. No less basis of tone, texture, relief, vegetation, soil tone and than thirty streams take their course from these hill drainage linearities and curvilinearities (Fig. 3). ranges which unite as they come downhill and form eleven sizable streams. The general fall on the hills is STRUCTURE to the north but they terminate abruptly into Utilizing Landsat Imagery, Drury and Holt (1980); precipitous cliffs in the south. These streams are Drury (1983) and Drury et al., (1984) deciphered the perennial, well supplied with water from the structural elements together with a regional model of innumerable springs arising out of joints in the rocks. tectonic evolution of south India. They recognized tectonics subdivisions in south India bounded by MATERIALS AND METHODS shear system along which crustal blocks have moved In the present study SOI toposheet no.58F/7, has laterally and vertically and along which crustal been used to digitize contour values, drainages and shortening appears to have occurred. spot heights to generate DTM of the area and analysis Transcurrent shear belts which juxtapose dissimilar of drainage configuration. Extensive field work has Archaean blocks deserve special mention. South of been done to provide ground check validity to DTM northernmost granulite massifs, a number of nearly and drainage patterns. E-W trending shear zones cut the terrane (Fig. 1b). The contour map of the area has been prepared by These may be connected to the N-S thrust system of digitizing contours using GIS software. The contour the Eastern Ghats by a multiplicity of small arcuate ranges from 400 to 2250 meter at the interval of 20 shears at the eastern extremity of the E-W shear meter. The spot heights given in toposheet have been system (Drury and Holt, 1980). The most important digitized to create spot height point map. of these are the Moyar-Bhavani and Palghat-Cauvery The DTM of the study area has been prepared by Shear System. Together, they form a dextral oblique- interpolation of rasterised segment contour map and slip shear system. Drury et al., (1984) estimated that Online version available at: www.crdeep.org 62 International Journal of Basic and Applied Sciences Prakash et. al., Vo. 1 No. 1 ISSN: 2277-1921 the shear system involves a dextral lateral shift of trend of NW-SE and have a moderate northeasterly c.70 km. The structural trend swing from N-S in the dip . Prominent mineral lineations in the present area region north of the shear system through NE-SW, to near Tinna Varai are defined by parallel arrangement E-W within the most intensely sheared zone. of biotites and prismatic crystals of sillimanite in garnet-cordierite sillimanite gneiss respectively. Figure 2. Digital Terain Model of the study area Figure 3. Remote sensing satellite data showing showing geomorphic features, trends of lineaments geomorphic features, trends of lineaments and and drainage pattern. drainage patterns of the study area. The strike and attitude of both compositional banding The lineament pattern has been deduced from the and tectonic fabric are extremely variable in the DTM and remote sensing satellite data (Fig. 2, 3). southern block. In the Palani Hills, the regional Some of the lineaments are showing curvilinear attitude of the planer fabrics changes eastwards from pattern and majority of them are striking in NNW- virtually flat-lying to a NNE-SSW strike with steep SSE direction. Another lineament trend i.e. ENE- WNW dip and defines an extremely large wave WSW is also common. In south-eastern part of the length, southward closing, north-ward-plunging study area few arcuate shape of lineament has been synform between the Annamalai Hills in the west and noticed (Fig. 4 a, b). Extensive field work suggests Kodaikanal in the east. that the study area is entirely bedrock terrain having To the east of the Kodaikanal massif a major high elevated structural ridges and adjacent structural lithological and structural change occurs where valleys striking NNW-SSE and ENE-WSW. As the supracrustal rocks become dominant, although they lineaments are weak zones provide significant are interlayered with granulite sheets. The regional information regarding tectonics of the area, field strike of the supracrustals and granulite sheets is NE- observation indicates that these WNW-ESE and SW, roughly conformable to the banding/fabric of the ENE-WSW striking lineaments are in actual Kodaikanal massif and parallel to its eastern margin. representing either the fold axis or fault planes Key structural feature of this supracrustal rock zone present in the form of ridges and valleys. The is an array of isoclinal folds, comprising the Porandalar River, which course is roughly from SW Varushanad and Andipatti Hills west of Madurai to NE, appears to follow a synclinal fold axis as rocks (Drury et al., 1984). The regional fabric and fold of either sides of the river dipping towards each patterns of the Kodaikanal and Madurai areas are other.