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      https://www.ias.ac.in/article/fulltext/jess/121/01/0001-0017

    • Keywords

       

      Poly-phase metamorphism; superposed folding; Chilka Lake granulites; Eastern Ghats Belt; oblique collision.

    • Abstract

       

      Granulite-facies rocks occurring north-east of the Chilka Lake anothosite (Balugan Massif) show a complex metamorphic and deformation history. The M1$–$D1 stage is identified only through microscopic study by the presence of S1 internal foliation shown by the M1 assemblage sillimanite–quartz–plagioclase–biotite within garnet porphyroblasts of the aluminous granulites and this fabric is obliterated in outcrop to map-scale by subsequent deformations. S2 fabric was developed at peak metamorphic condition (M2$–$D2­) and is shown by gneissic banding present in all lithological units. S3 fabric was developed due to D3 deformation and it is tectonically transposed parallel to S2 regionally except at the hinge zone of the F3 folds. The transposed S2/S3 fabric is the regional characteristic structure of the area. The D4 event produced open upright F4 folds, but was weak enough to develop any penetrative foliation in the rocks except few spaced cleavages that developed in the quartzite/garnet–sillimanite gneiss. Petrological data suggest that the $M_{4}–D_{4}$ stage actually witnessed reactivation of the lower crust by late distinct tectonothermal event. Presence of transposed $S_{2}/S_{3}$ fabric within the anorthosite arguably suggests that the pluton was emplaced before or during the $M_{3}–D_{3}$ event. Field-based large-scale structural analyses and microfabric analyses of the granulites reveal that this terrain has been evolved through superposed folding events with two broadly perpendicular compression directions without any conclusive evidence for transpressional tectonics as argued by earlier workers. Tectonothermal history of these granulites spanning in Neoproterozoic time period is dominated by compressional tectonics with associated metamorphism at deep crust.

    • Author Affiliations

       

      Kaushik Das1 Sankar Bose2 Subrata Karmakar3 Supriya Chakraborty2

      1. Department of Earth Sciences, Bengal Engineering and Science University, Shibpur, Howrah, India.
      2. Department of Geology, Presidency University, Kolkata, India.
      3. Department of Geological Sciences, Jadavpur University, Kolkata, India.
    • Dates

       
  • Journal of Earth System Science | News

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