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Summary of the Structural History of the Pre-Delhi Rocks around Sangat, Udaipur District, Central Rajastfian


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1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, India
     

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The metamorphic and migmatitic rocks comprising the Banded Gneissic Complex, the Aravallis and the Raialos around Sangat (25° O5': 73° 45'), central Rajasthan, maintain a structural unity with no decipherable unconformity within them. The rocks have been involved in two generations of folding with the earlier set dominant in the eastern part. The early folds are isoclinal and reclined, with their axial planes dipping and fold axes plunging W to WNW. On these is superimposed a set of open, upright, NNE-trending folds resulting in a dispersal of the earlier axial orientation near Sangat. Further west, with increase in the intensity of the second deformation, the later folds become isoclinal, the earlier axial planes are rotated to vertical attitude, and the traces of the earlier folds are lost except for occasional sharply bent reclined fold hinges. Because of the diverse orientation of the foliation surfaces already folded by the first movement, the later fold axes also show a great variation in plunge.

Disharmonic folding, curving foliation around the fold hinges, absence of planar surfaces oblique to the folded foliation, and folds following the competency rule prove that both the sets of folds were formed essentially by flexural slip. Early mullions unrollable on later axes also point to a flexural slip origin for the later folds.


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  • Summary of the Structural History of the Pre-Delhi Rocks around Sangat, Udaipur District, Central Rajastfian

Abstract Views: 226  |  PDF Views: 4

Authors

K. Naha
Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, India
A. K. Chaudhuri
Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, India
A. C. Bhattacharya
Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, India

Abstract


The metamorphic and migmatitic rocks comprising the Banded Gneissic Complex, the Aravallis and the Raialos around Sangat (25° O5': 73° 45'), central Rajasthan, maintain a structural unity with no decipherable unconformity within them. The rocks have been involved in two generations of folding with the earlier set dominant in the eastern part. The early folds are isoclinal and reclined, with their axial planes dipping and fold axes plunging W to WNW. On these is superimposed a set of open, upright, NNE-trending folds resulting in a dispersal of the earlier axial orientation near Sangat. Further west, with increase in the intensity of the second deformation, the later folds become isoclinal, the earlier axial planes are rotated to vertical attitude, and the traces of the earlier folds are lost except for occasional sharply bent reclined fold hinges. Because of the diverse orientation of the foliation surfaces already folded by the first movement, the later fold axes also show a great variation in plunge.

Disharmonic folding, curving foliation around the fold hinges, absence of planar surfaces oblique to the folded foliation, and folds following the competency rule prove that both the sets of folds were formed essentially by flexural slip. Early mullions unrollable on later axes also point to a flexural slip origin for the later folds.