The Deformation and Strain Analysis of the Gandemara Conglomerate from the Archaean Iron-Ore Group Rocks, District Singhbhum, Bihar

The Archaean I.O.G. metasediments exposed near Gandemara have undergone three successive deformational phases, D₁, D₂ and D₃ of varying intensities. The quartzite pebbles from oligomictic conglomerate arc considered as the markers for finite strain analysis. Strong correlation between major and minor axes of the ellipses (sections of the pebbles along XY, YZ and XZ planes) and good linear fitting to the axial-ratio plots imply that these markers came from the same population. High values of fluctuation 'φ' and nearly symmetric Rf/φ patterns (IYSM values) indicate large initial axial-ratios (Ri >Rs) and random predeformational fabric respectively. The axial-ratios of strain ellipses (Rs) in XY, YZ and XZ sections are 1.5, 1.83 and 2.5 respectively and these correspond closely with the β values. The three dimensional strain analysis reveals that most of the pebbles have undergone flattening (γ=0.2 to 0.4) corresponding to the low amounts of strain (ε_s =0.6 to 1.0). Available structural relations and evidences from strain analysis strongly suggest that the conglomerate has been dominantly deformed during D₁ phase and subsequently modified during D₂ phase.