Informatics Publishing Limited

T. K. Biswal ¹, G. Sanjeevan ¹, B. P. Nayak ¹

Affiliations
1 Indian Institute of Technology, Dept. of Earth Sciences, Powai, Mumbai-400 076, IN

Abstract

The calc-gneiss and garnet-sillimanite-gneiss of Eastern Ghat Mobile Belt around Lathore bear the imprint of multiple phases of deformtion. The folds of the first generation, F₁, are isoclinal, intrafolial and vary in style from reclined to upright. This has developed a pervasive axial planar gneissosity. The second generation folds, F₂ , which are coaxial with the F₁ are open to tight with a planar axial surface dipping moderately to SE and varied plunging axis. At places mesoscopic plane non-cylindrical F₂ sheath folds are noticed. Gentle upright folds, F₃ , with NW-SE striking axial plane represent structure of third generation. Superimposition of F₂ on F₁ has resulted in Type 3 interference pattern and dome and basin structures are due to the interference of F₂ and F₃ folds. F₁ and F₂ folds are attributed to WNW-ESE buckling and F₃ is reported to be due to shortening across it. The 'sheath folds' are due to heterogeneous simple shear aiong the axial plane of the F₂ fold. The map shows a large scale southwesterly plunging overturned F₂ fold. Post-exhumation deformation has resulted in brittle shearing parallel to the axial plane of F₂ fold. The structure of the area points to a collisional tectonic setting like other granulite belts of Gondwanaland.

Keywords

Structural Geology, Eastern Ghat Mobile Belt, Orissa.

Full Text

     

Richa Sahu ¹, Anil Kumar ², K. V. Subbarao ¹, J. N. Walsh ³, T. K. Biswal ¹

Affiliations
1 Indian Institute of Technology, Mumbai - 400 076., IN
2 National Geophysical ,Research Laboratory, Hyderabad - 500 007., IN
3 Royal Holloway, University of London, Egham, Surrey TW20 OEX, GB

Abstract

No Abstract.

Full Text

   

T. K. Biswal ¹, Sunayana Sarkar ¹, Aditi Pal ¹, Urmi Chakraborty ¹

Affiliations
1 Indian Institute of Technology, Powai, Mumbai - 400 076, IN

Abstract

Cataclasites-pseudotachylites are developed along the Kui-Chitraseni shear zone of the Aravalli Mountain. The pseudotachylites are microlitic belonging to three varieties referred to here as patchy-, vein- and fracture- pseudotachylites. The patchy pseudotachylites are the most dominating type that occur in association with cataclasites and show an increase in abundance from the margin of the shear zone towards the center. Vein pseudotachylites owe their origin to the injection of the patchy variety through extensional fractures. Fracture pseudotachylites, the youngest of all, occur along the late stage shear fractures. Presence of vesicles, flow texture, embayed margin of the clasts in addition to power law distribution of coarser clasts and high values of roundness (0.4) support the melt origin of the pseudotachylites. Ultracataclasis followed by frictional melting of the Erinpura granites along the shear zone is ascribed for the development of the cataclasites and pseudotachylites.

Keywords

Pseudotachylites, Melt Origin, Kui-Chitraseni Shear Zone, Aravalli Mountain, Erinpura Granite.

Full Text

     

T. K. Biswal ¹, S. K. Jena ¹, S. Datta ¹, R. Das ¹, K. Khan ¹

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology, Powai, Mumbai, 400 076, IN

Abstract

The terrane boundary between Eastern Ghats Mobile Belt and the Bastar Craton in Balangir and Kalahandi Districts of Orissa is distinctly marked by nearly two kilometer wide southeasterly dipping ductile shear zone, designated as the Lakhna shear zone. The shear zone has largely developed in the craton, but for a narrow width within the Fastern Ghats. It is dominated by quartzofcldspathic mylonites characterised by S-C fabric, asymmetric winged porphyroclasts, quartz ribbons and intragranuhr faults. These structures have been effectively utilized in deducing the sense of shear and evaluating the amount of strain. The results show thrusting of the Eastern Ghats over the Bastar Craton. The minimum amount of throw along the thrust has becn estimated to be around 2.5 to 4.7 km assuming a dominant simple shear deformation.

Keywords

Terrane Boundary, Lakhna Shear Zone, Strain Evaluation, Eastern Ghats Mobile Belt, Bastar Craton, Orissa.

Full Text

     

T. K. Biswal ¹, V. Thirukumaran ², Kamleshwar Ratre ¹, Krishanu Bandyapadhaya ¹, K. Sundaralingam ¹, Amit Kumar Mondal ¹

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

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.

Full Text