Comparison of the Tarikere Valley Gneiss and the Gneiss Pebbles in the Kaldurga Conglomerate -A Study in the Dharwar Basement Problem

Kaldurga conglomerate of the Precambrian Dharwar Group contains 3250±150 m.y. old gneiss pebbles. Controversy exists as to whether the 'Peninsular gneiss' adjoining the conglomerate in the Tarikere valley contributed the pebbles or whether the gneiss is a remobilised product of the precursor gneiss that contributed to the pebbles.

A comparative petrographic study of the Kaldurga pebble gneiss (KPG) and the Tarikere valtey gneiss (TVG) shows that, although both have a tonalitic composition, the TVG are enriched in Ca and Ti, reflected in the abundance of sphene and apatite. Texturally, the Kaldurga pebbles are catac1astically deformed. TVG are comparatively free from such structures, and are characterised by syntectonic recrystallization textures.

TVG have greater Ti abundance than the KPG, and the latter are comparable to the Ti abundance levels of Archaean gneisses. The higher Ti abundance levels in the TVG suggests their evolution through remobilisation and supracrustal contamination.