• Geology, geochemistry and geochronology of the Archaean Peninsular Gneiss around Gorur, Hassan District, Karnataka, India

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    • Keywords

       

      Archaean; trondhjemites; geochemistry; Rb-Sr geochronology; Peninsular gneiss; syntectonic emplacement; evolution of continental crust

    • Abstract

       

      The Peninsular Gneiss around Gorur in the Dharwar craton, reported to be one of the oldest gneisses, shows nealy E-W striking gneissosity parallel to the axial planes of a set of isoclinal folds (DhF1). These have been over printed by near-coaxial open folding (DhF12) and non-coaxial upright folding on almost N-S trend (DhF2). This structural sequence is remarkably similar to that in the Holenarasipur schist belt bordering the gneisses as well as in the surpracrustal enclaves within the gneisses, suggesting that the Peninsular Gneiss has evolved by migmatization synkinematically with DhF1 deformation.

      The Gorur gneisses are high silica, low alumina trondhjemites enriched in REE (up to 100 times chondrite), with less fractionated REE patterns (CeN/YbN < 7) and consistently negative Eu anomalies (Eu/Eu* = 0.5 to 0.7).

      A whole rock Rb-Sr isochron of eight trondhjemitic gneisses sampled from two adjacent quarries yields an age of 3204 ± 30 Ma with Sri of 0.7011 ± 6 (2σ). These are marginally different from the results of Beckinsale and coworkers (3315 ± 54 Ma, Sri = 0.7006 ± 3) based on a much wider sampling. Our results indicate that the precursors of Gorur gneisses had a short crustal residence history of less than a 100 Ma.

    • Author Affiliations

       

      Y J Bhaskar Rao1 K Naha1 2 R Srinivasan1 K Gopalan1

      1. National Geophysical Research Institute, Hyderabad - 500 007, India
      2. Indian Institute of Technology, Kharagpur - 721 302, India
    • Dates

       
  • Journal of Earth System Science | News

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