Structural and textural development in Singhbhum shear zone,eastern India |
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| Authors: | Dhruba Mukhopadhyay Gautam Kumar Deb |
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| Institution: | (1) Department of Geology, University of Calcutta, 35, Ballygunge Circular Road, 700019 Calcutta, India;(2) Geological Studies Unit, Indian Statistical Institute, 700035 Calcutta, India |
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| Abstract: | The rocks within the Singhbhum shear zone in the North Singhbhum fold belt, eastern India, form a tectonic melange comprising
granitic mylonite, quartz-mica phyllonite, quartz-tourmaline rock and deformed volcanic and volcaniclastic rocks. The granitic
rocks show a textural gradation from the least-deformed variety having coarse-to medium-grained granitoid texture through
augen-bearing protomylonite and mylonite to ultramylonite. Both type I and type II S-C mylonites are present. The most intensely
deformed varieties include ultramylonite. The phyllosilicate-bearing supracrustal rocks are converted to phyllonites. The
different minerals exhibit a variety of crystal plastic deformation features. Generation of successive sets of mylonitic foliation,
folding of the earlier sets and their truncation by the later ones results from the progressive shearing movement. The shear
sense indicators suggest a thrust-type deformation. The microstructural and textural evolution of the rocks took place in
an environment of relatively low temperature, dislocation creep accompanied by dynamic recovery and dynamic recrystallization
being the principal deformation mechanisms. Palaeostress estimation suggests a flow stress within the range of 50–190 MPa
during mylonitization. |
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| Keywords: | Singhbhum shear zone mylonites texture shear sense indicators |
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