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The 'Dharwar System' and its Position in the Indian Precambrian


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1 Department of Geology, Andhra University, Waltair, India
     

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Bruce Foote gave the name 'Dharwar System' to the 'Lower Transition' rocks occurring near Dharwar in Mysore State, when he first separated these schistose rocks from the 'great granitoid gneiss system'.

It was Fermor, however, who generalized the term and commended its use for designating all the sedimentary schists lying below the Eparchaean unconformity. Lithological resemblances constituted an important factor in the correlation of these ancient schistose formations, and for the identification of 'Dharwar' rocks in many parts of India. The occurrences in widely separated areas, of crystalline limestones, manganese-bearing rocks, banded ferruginous quartzites and iron ores, and even calc-granulites and pyroxene gneisses, have been used as criteria not only for assigning certain formations to the Dharwars, but also as indicating the homotaxial relationship of these formations scattered in different parts of India. By doing so, the stratigraphical importance of certain types of rocks have been exaggerated, in the unfounded belief that some types of sediments were formed only at certain specific periods in the geological history of the earth.

Recent work has shown that Peninsular India like other shield areas of the world, exhibits an ingrained pattern of successive orogenic belts. Age determinations and the dispositions of the tectonic units of the Precambrian formations, indicate that the oldest rocks are found In Mysore State in southern India, which is the type area for the Dharwars (c. 2300 m.y.). This region possesses several important characteristics of a continental nucleus, and is bounded on the east by the Eastern Ghats province (c. 1600 m.y.), and on the north by the Satpura province (c. 1000 m.y.). These provinces must be considered as later Precambrian accretions composed of younger sediments with their own orogenic cycles, and so the real Dharwars are older than both the Eastern Ghats and Satpura belts.

It is necessary, therefore, to discontinue the use of the term 'Dharwar' to designate the schistose rocks outside the type area, because all these un fossiliferous deposits cannot be considered as synchronous or even homotaxial, since some of the lithologically similar rocks are known now to be associated with younger orogenic cycles.

The term 'Dharwar System' should be strictly confined to the schistose rocks of the type area in the continental nucleus situated in South India.


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  • The 'Dharwar System' and its Position in the Indian Precambrian

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Authors

C. S. Pichamuthu
Department of Geology, Andhra University, Waltair, India

Abstract


Bruce Foote gave the name 'Dharwar System' to the 'Lower Transition' rocks occurring near Dharwar in Mysore State, when he first separated these schistose rocks from the 'great granitoid gneiss system'.

It was Fermor, however, who generalized the term and commended its use for designating all the sedimentary schists lying below the Eparchaean unconformity. Lithological resemblances constituted an important factor in the correlation of these ancient schistose formations, and for the identification of 'Dharwar' rocks in many parts of India. The occurrences in widely separated areas, of crystalline limestones, manganese-bearing rocks, banded ferruginous quartzites and iron ores, and even calc-granulites and pyroxene gneisses, have been used as criteria not only for assigning certain formations to the Dharwars, but also as indicating the homotaxial relationship of these formations scattered in different parts of India. By doing so, the stratigraphical importance of certain types of rocks have been exaggerated, in the unfounded belief that some types of sediments were formed only at certain specific periods in the geological history of the earth.

Recent work has shown that Peninsular India like other shield areas of the world, exhibits an ingrained pattern of successive orogenic belts. Age determinations and the dispositions of the tectonic units of the Precambrian formations, indicate that the oldest rocks are found In Mysore State in southern India, which is the type area for the Dharwars (c. 2300 m.y.). This region possesses several important characteristics of a continental nucleus, and is bounded on the east by the Eastern Ghats province (c. 1600 m.y.), and on the north by the Satpura province (c. 1000 m.y.). These provinces must be considered as later Precambrian accretions composed of younger sediments with their own orogenic cycles, and so the real Dharwars are older than both the Eastern Ghats and Satpura belts.

It is necessary, therefore, to discontinue the use of the term 'Dharwar' to designate the schistose rocks outside the type area, because all these un fossiliferous deposits cannot be considered as synchronous or even homotaxial, since some of the lithologically similar rocks are known now to be associated with younger orogenic cycles.

The term 'Dharwar System' should be strictly confined to the schistose rocks of the type area in the continental nucleus situated in South India.