Structural characteristics of the rocks of the Delhi Supergroup with special reference to interference patterns: An appraisal with some examples from Central Rajasthan

The rocks of the Delhi Supergroup, which occur around Barr-Sendra and Phulad-Deogarh regions in Central Rajasthan, show three phases of deformational episodes: (i) phase D₁—tight-to-long limbed isoclinal fold (F₁); phase D₂—open, asymmetric fold (F ₂) controlling the map pattern of the formational boundaries; and (iii) phase D₃—major warps (F₃). Interference between nearly coaxial F₁ and F₂ on northerly axes produced hook-shaped and crescent patterns whereas superimposition of easterly trending F₃ on F₂ produced dome-and-basin patterns. The thermal peak was achieved during the second phase of deformation when the rocks were constructively metamorphozed and granites (850−750 m.y.), late synkinematic with respect to second phase of deformation, were emplaced. The sequence of deformation and the structural pattern of the rocks of the Delhi Supergroup in Central Rajasthan strikingly resemble those in northeastern Rajasthan. Structurally the characteristics of the Delhi Supergroup as verified in the entire region from NE to Central Rajasthan are: (a) the same sequence of development of folds, F₁, F₂ and F₃, interspersed with nearly identical phases of recrystallization, (b) hook-shaped interference pattern due to near-coaxial refolding of F₁ by F₂, and (c) variation in axial plunge of F₂ resulting in culminations and depressions. Lastly, phases of the recrystallization history indicates little time gap between F₁ and F₂, and a considerable gap between F₂ and F₃.