Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Dhruba Mukhopadhyay ¹, Sabyasachi Dasgupta ¹, Kunal Dhar ¹

Affiliations
1 Department of Geology, Presidency College, Calcutta 700073, IN

Abstract

A sequence of metasediments with conglomerate at the base, unconformably overlies the Singhbhurn Granite. The direction of younging in the arkose-conglomerate is towards north, away from the granite border. Wedges of basement granite were emplaced as thrust slices within the metasediments at the earliest stage of deformation. The soda granite also occurs as a sheet like concordant body and is highly deformed and in places rnylonitized. The soda granite may also represent a tectonically emplaced slice of the basement.

Full Text

     

C. P. Vohra ¹, Sabyasachi Dasgupta ¹, D. K. Paul ¹, P. K. Bishui ¹, S. N. Gupta ¹, S. Guha ¹

Affiliations
1 Geological Survey of India, Calcutta - 700 016, IN

Abstract

The tonalitic suite of Kaptipada is high-Al₂O₃ type with a highly fractionated REE pattern suggesting its derivation by partial melting of amphibolite with hornblende as a residual phase. The homblende/biotite-bearing granites of Nilgiri and Ramapahari areas also occurring along the southeastern fringe,are comparatively K-rich than the lonalite-granodiorite suite of Kaptipada. Based on whole rock Rb-Sr isotopic analyses, lhe Kaptipada tonalite-granodiorite suite yields an age of 3275 ± 81 Ma with initial Sr ratio of O.70130± 0.00045; ... the Nilgiri granite, an age of 2366 ± 126Ma with initial Sr ratio of 0.72526 ± 0.00832 and Ramapahari granite, an age of 1895 ± 46 Ma wilh initial Sr ratio of 0.76521 ± 0.00427.

The temporal evolution of the tonalitic rocks of Kaptipada is indistinguishable from the earlier phases of Singhbhum and Bonai granitoids of the Singhbhum Craton. It is concluded that an extensive growth of tonalitic crust took place around 3.3 Ga in the region.

Keywords

Isotopic Study, Rb-Sr Chronology, Geochemistry, Tonalitic Granite, Crustal Evolution, Singhbhum Craton, Orissa.

Full Text