Evolution of microstructures in Precambrian shear zones: An example from eastern India |
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| Institution: | 1. Geoscience/Seismology Division, Ministry of Earth Sciences, New Delhi, India;2. National Center for Seismology, Ministry of Earth Sciences, New Delhi, India;3. Dept. of Geophysics, Andhra University, Visakhapatnam, India;1. Faculdade de Engenharia, Universidade do Estado de Minas Gerais, João Monlevade, MG, Brazil;2. Instituto de Geociências, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil;3. Universidade do Estado do Amazonas, Manaus, AM, Brazil;4. Centre for Exploration Targeting, University of Western Australia, Perth, WA, Australia;5. Centre for Excellence in Ore Deposits, University of Tasmania, Hobart, Tasmania, Australia;6. Centro Federal de Educação Tecnológica de Minas Gerais, Belo Horizonte, MG, Brazil;1. Department of Geology, University of Dschang, P.O. Box 67, Dschang, Cameroon;2. Geowissenschaftliches Zentrum Göttingen, Georg-August-Universität Göttingen, Goldschmidt-Straße 1, 37077, Göttingen, Germany;3. Department of Life and Earth Sciences, Higher Teachers'' Training College, University of Maroua, P.O. Box 55, Maroua, Cameroon;4. Ministry of Mines, Industry and Technological Development, P.O. Box 70, Yaoundé, Cameroon;5. Ministry of Scientific Research and Innovation, DPSP / CCAR, P.O. Box 1457, Yaoundé, Cameroon;6. Laboratory of Geology, ENS, University of Yaoundé I, P.O. Box 47, Yaoundé, Cameroon |
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| Abstract: | Shear zones are areas of intense deformation in localized zones which can be used as natural laboratories for studying deformation characteristics. Metre to-micro scale structures that develop in response to a progressive simple shear in a shear zone are characterized by a protracted history of deformation and are immensely useful in delineating the history of progressive deformation. To decipher these localized zones of deformation and to establish the continuous non-coaxial character of deformation, detail microstructural studies are very useful. Singhbhum shear zone (SSZ), a regional Precambrian tectonic dislocation zone in eastern India, depicting a top-to-south thrust movement of the hanging wall provides a scope for studying microstructural characteristics developed in response to a progressive shear at mid-crustal level. SSZ is characterized by intense stretching lineation, isoclinal folds, shear planes, superposed schistosity and deformed quartz veins. Quasi-plastic (QP) deformation mechanisms were predominantly active in the SSZ. The overprinting relationship between the earlier and later schistosity with a consistent sense of shear indicates that earlier schistosity is transposed to later schistosity through the intermediate stages of crenulation cleavage during a progressive non-coaxial deformation. The recrystallization of quartz in mylonitic quartzite suggests protracted history of deformation. The analysis of the character of quartz grains of both the porphyroclasts and recrystallized grains suggests that strain was partitioned between the most intensely deformed central part of the shear zone and the shear-related deformation zone outside the central part of the shear zone. |
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