Geochronology of the Granitoids of the Kunjar Area, Sundergarh District, Orissa: Implications to the Regional Stratigraphy

Rb-Sr isotopic data for the Tamparkola granite, northwest of Bonaigarh, and Bamra granite, southeast of Barnra, Sundergarh district, Orissa have yielded similar ages of 2746&#177144 Ma and 2738±28 Ma, respectively. Small granite exposures intruding the Iron Ore Group in the southern part of Tamparkola granite, have also indicated similar Whole Rock Rb-Sr age of 2867&#17786 Ma. These may be correlated with the Bonai granite. Significant crustal component was involved in the generation of these granites, as indicated by high initial Sr ratio, and their emplacement probably marks a major terminal cratonisation event in northwestern part of the Singhbhum-North Orissa Craton.

Ths study does not support the view that the Tamparkola Granite is equivalent to the Itrna/Ekma granites that are intrusive into the Gangpur Group. These age results call for a revision of the stratigraphy of the Bonai-Gangpur tract, in that the Darjing Group unconformably overlies both the Bonai granite and Tamparkola granite, with the Mesoproterozoic Kunjar sedimentary sequence representing the youngest of the regional succession.