Transformation of Peninsular Gneiss into Charnockite in Mysore State, India

A preliminary account is given in this paper of an example of rock transformation from near the village of Kabbal in southern Mysore State. In an area which is predominantly composed of Peninsular Gneiss, there is a development of charnockite in patches of varying shapes and dimensions. The gneiss is grey. banded and often contorted. It is generally biotitic but contains inclusions of hornblende schist. The charnockite is coarse-grained, greasy looking, and brownish-green in colour. Hypersthene occurs in big crystals. The gneissic foliations can often be traced right through the charnockitc patches,-evidence of the transformation of the banded gneisses into coarse grained charnockites.

Photographs taken in the field and photomicrographs of thin sections of some of the rock types illustrate stages in this interesting mode of formation of charnockites in Peninsular India.

The geological sketch map shows the position of Kabbal in relation to the occurrence of charnockites further south, in and towards the east of the Biligirirangan Hills, an area which forms part of the huge Nilgiri massif in Madras State. The locality described in this paper appears to be situated on the border of a zone of charnockitization where stages in the transformation of foliated gneiss into coarse charnockitc can be seen.