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A Study of Mylonites from Parts of the Salem-Attur Shear Zone (Tamil Nadu) and its Tectonic Implications


Affiliations
1 Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, India
2 Department of Geology, Govt. Arts College, Salem-636 007, India
     

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The E-W running Salem-Attur shear zone demarcates the tectonic boundary between Archaean Dharwar Craton in the north and Proterozoic Southern granulite terrane in the south. This study reveals that the shear zone is a low angle thrust. The thrust zone is around 10 m thick and it merges with the main shear zone along the strike. The thrust is developed on charnockite near Odyarpatti, which is retrograded into schists. Further, it is marked by gently dipping mylonitic foliation and subhorizontal lineation. The S-C fabric, mantled porphyroclasts and intragranular faults indicate northeasterly slip along the thrust. Recumbent shear folds SF1 are developed within the thrust zone. The thrust has been folded by late stage F2 fold which has brought variation in the orientation of the mylonitic foliation from subhorizontal to vertical attitude; the mylonitic lineations have been rotated to subvertical orientation also. Additionally, the F2 crenulations and shear cleavages and intersection lineations are superimposed on the mylonitic fabric. Thrusting along the Salem-Attur shear zone is probably the cause for upliftment of the charnockites to the upper crust. Post-upliftment stage has witnessed brittle deformation in the form of development of shear fractures in NNE-SSW and E-W directions. Pseudotachylites are emplaced along these fractures.

Keywords

Mylonites, Pseudotachylites, Low Angle Thrust, Salem-Attur Shear Zone.
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  • A Study of Mylonites from Parts of the Salem-Attur Shear Zone (Tamil Nadu) and its Tectonic Implications

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Authors

T. K. Biswal
Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, India
V. Thirukumaran
Department of Geology, Govt. Arts College, Salem-636 007, India
Kamleshwar Ratre
Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, India
Krishanu Bandyapadhaya
Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, India
K. Sundaralingam
Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, India
Amit Kumar Mondal
Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, India

Abstract


The E-W running Salem-Attur shear zone demarcates the tectonic boundary between Archaean Dharwar Craton in the north and Proterozoic Southern granulite terrane in the south. This study reveals that the shear zone is a low angle thrust. The thrust zone is around 10 m thick and it merges with the main shear zone along the strike. The thrust is developed on charnockite near Odyarpatti, which is retrograded into schists. Further, it is marked by gently dipping mylonitic foliation and subhorizontal lineation. The S-C fabric, mantled porphyroclasts and intragranular faults indicate northeasterly slip along the thrust. Recumbent shear folds SF1 are developed within the thrust zone. The thrust has been folded by late stage F2 fold which has brought variation in the orientation of the mylonitic foliation from subhorizontal to vertical attitude; the mylonitic lineations have been rotated to subvertical orientation also. Additionally, the F2 crenulations and shear cleavages and intersection lineations are superimposed on the mylonitic fabric. Thrusting along the Salem-Attur shear zone is probably the cause for upliftment of the charnockites to the upper crust. Post-upliftment stage has witnessed brittle deformation in the form of development of shear fractures in NNE-SSW and E-W directions. Pseudotachylites are emplaced along these fractures.

Keywords


Mylonites, Pseudotachylites, Low Angle Thrust, Salem-Attur Shear Zone.

References