Relief and Structure of Karnataka

Karnataka has representatives of all types of variations in topography – high mountains, plateaus, residual hills and coastal plains. The State is enclosed by chains of mountains to its west, east and south.

It consists mainly of plateau which has higher elevation of 600 to 900 metres above mean sea level. The entire landscape is undulating, broken up by mountains and deep ravines.

Plain land of elevation less than 300 metres above mean sea level is to be found only in the narrow coastal belt, facing the Arabian Sea. There are quite a few high peaks both in Western and Eastern Ghat systems with altitudes more than 1,500 metres mark the Relief and Structure of Karnataka.

A series of cross-sections drawn from west to east across the Western Ghat generally exhibit, a narrow coastal plain followed to the east by small and short plateaus at different altitudes, then suddenly rising upto great heights.Then follows the gentle east and east-north-west sloping plateau. Among the tallest peaks of Karnataka are the Mullayyana Giri (1,925 m), Bababudangiri (Chandradrona Parvata 1,894 m) and the Kudremukh (1,895 m) all in Chikmagalur district and the Pushpagiri (1,908 m) in Kodagu district. There are a dozen peaks which rise above the height of 1,500 metres. Physiograpically, Karnataka State forms part of two well defined macro regions of Indian Union; the Deccan Plateau and the Coastal plains and Islands. The State has four physiographic regions

· Northern Karnataka Plateau

· Central Karnataka Plateau

· Southern Karnataka Plateau

· Karnataka Coastal Region

Geology of Karnataka

Karnataka forming a part of the Indian Shield is constituted of rock formations ranging in age from 3300 m.y. to 5 m.y. Barring a narrow coastal strip of about 5000 sq.km of Tertiary and Quaternary sediments and another 31,250 sq.km of Deccan basalts, the remaining area is dominated by Archaean-Proterozoic rocks. Mysore Plateau, geologically constituted of Dharwar Craton comprises of greenstone-granite belts, gneisses and granulites. Greenstone belts essentially consist of meta-volcanosedimentary sequences, surrounded and dissected by Peninsular Gneiss.

At the southern end of the craton these give way to granulite suite of rocks. The craton preserves a billion year orogenic history from 3400 m.a. to 2400 m.a. Epicratonic or intracratonic sedimentary basins called Purana Basins occupy the northern segment of the craton whose northern part in turn is concealed by Deccan basalts. Thus younging of lithosequence from south to north is evident.

Sargur Group

Large scale, mega enclaves of high grade schistose rocks, south of Mysore around Sargur and in its adjacent areas were considered to be a distinct stratigraphic entity and older. These litho-assemblages are considered to be equivalent to the Dharwarian event by another school of workers. The important belts of western greenstone include Sargur (type area), Holenarsipur, Nuggihalli, Aladahalli, Kalyadi, Krishnarajpet, Ghattihosahalli .

Peninsular Gneissic Complex (PGC):

Peninsular Gneiss has a protracted evolutionary history extending over a period of time and therefore has no stratigraphic significance. The mineralogical characters of the gneiss vary greatly and dependent on the adjacent greenstones it has migmatised. Therefore this rock suite is said to be composite gneiss, formed by migmatisation of supracrustals in different phases at different stratigraphic levels. Most common variety of Peninsular Gneiss-I consist of quartz, microcline and oligoclase with traces of muscovite, apatite and zircon in the leucocratic part; biotite, hornblende and epidote by and large form the melanocratic component..

Charnockite:

These are essentially blue quartz-hypersthene bearing granular suite of rocks now broadly referred to as pyroxene granulite. These are confined to a 30 km wide transition zone between the low grade gneissic terrain in the north and high grade granulite terrain to its south. They occupy Biligiri Rangan hills, Male Mahadeswara hills in Mysore District, southern segment of Coorg District, set in a regional trend of northwest to southeast. These isolated massifs of charnockite are said to be the product of later regional thermal metamorphism with fluids driven from deeper part of the crust playing a vital role in its transformation. Charnockite with protoliths of younger age of 2600 Ma is recorded from the greenstone-granulite transitional zone of Kabbal-Kushalnagar areas.

Greenstone Belts

Greenstone belts of Karnataka attracted the attention of geological community, both for its complex geological history and rich mineral resources. The era of 2900 million years to 2600 million years witnessed this great event of the evolution of Greenstone belts in Karnataka. Stratigraphic level vis-à-vis geochronological positioning of different schist belts had always been a point of endless yet useful debate. Large scale, mega enclaves of high grade schistose rocks, south of Mysore around Sargur and in its adjacent areas were considered to be a distinct stratigraphic entity and older in age.

These litho-assemblages are also considered to be equivalent to that of Dharwarian event by another school of workers. The entire schistose rocks of Karnataka are broadly grouped into Eastern block true greenstone belts, Western block schistose belts. These two blocks are separated by the Chitradurga boundary fault near the western margin of Closepet Granite.

The later is further divisible into belts of green schist facies and of higher grade amphibolite facies as shown under: While describing the greenstone belts of Karnataka (1) Western block (Dharwar), (2) Western block (Sargur), (3) Eastern block (Dharwar), (4) Transitional belts are dealt as per the recent classification given by Ramakrishnan (1994). Litho-assemblage of western greenstone block of Dharwar Supergroup is divided into lower Bababudan Group, largely consisting of volcanic suites with shelf/platformal metasediments rich in iron and manganese precipitates; and the upper Chitradurga Group, that is largely made up of sedimentary sequence of

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