A tectonic analysis of the quartz reefs in the metamorphites of Tilatanr, Tetulmari (Dhanbad)

Abstract

Numerous quartz-filled faults occur in the metamorphites comprising mica-schists, granulites, injection gneisses, migmatites, amphibolites and hornblende gneisses of Dharwar age in the Tilatanr area. The metamorphites have been folded into a pitching anticline with drag folds on its limbs due to strong folding movements and deformation during Dharwar period. Quartz-filled faults occur not only as individual ones but also as zones. Various structures have been noticed in the quartz of the quartz-filled faults, namely, box-works, honeycomb-texture, platy quartz, shear fractures, tension joints and joint drags. Faults are later than folds and hence they are incongruous with the folds. On tectonic analysis it has been found that there are two types of faults, namely, high angle shear thrusts (reverse faults) and normal faults. Normal faults are later than the shear thrusts and they represent the latest adjustment of rocks to deformation. Shear thrusts are parallel to the strike of the beds and the regional structure and they are reverse faults. Associated with the shear thrusts occur shear fractures, tension joints and joint drags. These minor structures associated with the shear thrusts have been analysed and their relation to the structural axes have been described on the lines of Sander, and others.