Deformational and crystallization history of the Precambrian rocks in north-central Aravalli Mountain, Rajasthan, India

Abstract

Abstract Large-scale structures, textures and mineral assemblages in the Precambrian rocks of the Banded Gneissic Complex and the overlying Delhi Group in north-central Aravalli Mountain reveal a complex deformational-crystallization history. In the basement Gneissic Complex at least three deformational events, D 0 , D 1 and D 2 , and two separate episodes of metamorphism, M 1 and M 2 , are recognized. The supracrustal Delhi Rocks display only two phases of deformation, D 1 and D 2 , associated with a single protracted period of metamorphism, M 2 . The first phase of deformation (D 1 ) of the Delhi orogeny (1650-900 m.y.) produced large isoclinal folds that are overturned towards the southeast and have gentle plunges in NE and SW directions. The second phase of deformation (D 2 ) gave rise to tight open folds on the limbs and axial-plane surfaces of the D 1 folds. These folds generally plunge towards the N and NNW at 30°–80°. In the Basement Complex one more deformation (D 0 ) of the Pre-Delhi orogeny (> 2000 m.y.) is recorded by the presence of reclined and recumbent folds with W to WNW trending fold axes. The D 0 folds were superimposed by D 1 and D 2 folds during the Delhi orogeny. The three deformational events have been correlated with the crystallization periods of minerals in the rocks and a setting in time is established for this part of the Aravalli range.