Tectonomagmatic History of the Precambrians in Bellary District, Mysore State

A chronostratigraphic classification of the Precambrians in Bellary district, Mysore State, based on tectonomagmatic cycles in the evolution of geosynclinal facies is presented for the first time by the author. The older metamorphics are grouped under 'Archaeans' (2500 m.y. and above) and the Dharwars, under Proterozoic (2500-900 m.y.), Structurally four kinds of folds are described. The first cycle of folding, F1, consists of the earlier formed anticlines and synclines plunging northerly or NNW. The second cycle, F2, comprises asymmetric cross-folding of the earlier structures, plunge being parallel to the direction of plunge of the earlier folds. The third, F3, and the fourth, F4, cycles of folding consist of antiforms and Synforms on bedding and en echelon drag folds. the structural pattern in the district reveals that all the different tension and stress expressions are together consistent with orle general stress field, a horizontal compression.