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      https://www.ias.ac.in/article/fulltext/jess/099/02/0249-0268

    • Keywords

       

      North Singhbhum; Singhbhum shear zone; structural geometry; polyphase deformation; volcaniclastic rocks; lithological characteristics; deformation history

    • Abstract

       

      In the western part of the North Singhbhum fold belt near Lotapahar and Sonua the remobilized basement block of Chakradharpur Gneiss is overlain by a metasedimentary assemblage consisting of quartz arenite, conglomerate, slate-phyllite, greywacke with volcanogenic material, volcaniclastic rocks and chert. The rock assemblage suggests an association of volcanism, turbidite deposition and debris flow in the basin. The grade of metamorphism is very low, the common metamorphic minerals being muscovite, chlorite, biotite and stilpnomelane. Three phases of deformation have affected the rocks. The principal D1 structure is a penetrative planar fabric, parallel to or at low angle to bedding. No D1 major fold is observed and the regional importance of this deformation is uncertain. The D2 deformation has given rise to a number of northerly plunging major folds on E-W axial planes. These have nearly reclined geometry and theL2lineation is mostly downdip on theS2surface, though some variation in pitch is observed. The morphology of D2 planar fabric varies from slaty cleavage/schistosity to crenulation cleavage and solution cleavage. D3 deformation is weak and has given rise to puckers and broad warps on schistosity and bedding. The D2 major folds south of Lotapahar are second order folds in the core of the Ongarbira syncline whose easterly closure is exposed east of the mapped area. Photogeological study suggests that the easterly and westerly closing folds together form a large synclinal sheath fold. There is a continuity of structures from north to south and no mylonite belt is present, though there is attenuation and disruption along the fold limbs. Therefore, the Singhbhum shear zone cannot be extended westwards in the present area. There is no evidence that in this area a discontinuity surface separates two orogenic belts of Archaean and Proterozoic age.

    • Author Affiliations

       

      Dhruba Mukhopadhyay1 Tapas Bhattacharya2 Tapan Chakraborty3 Arun Kanti Dey4

      1. Department of Applied Geology, Indian School of Mines, Dhanbad - 826004, India
      2. Department of Earth and Planetary Sciences, Allahabad University, Allahabad - 211002, India
      3. Geological Studies Unit, Indian Statistical Institute, Calcutta - 700035, India
      4. Department of Geology, Presidency College, Calcutta - 700073, India
    • Dates

       
  • Journal of Earth System Science | News

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