The Shillong Basin is the only Proterozoic (Purana) basin of NE India and is an intracratonic sag basin in nature. The basin is dominantly exposed in Meghalaya and partly in Karbi Anglong district of Assam and confined in the central and eastern parts of the Shillong plateau. This Proterozoic basin was developed during early Mesoproterozoic time. The metasedimentary rock associations of this basin are classified under Lower Metapelitic and Upper Quartzitic Formations closely associated with mafic magmatism in the form of mafic sills and dykes (metadolerite, locally named as Khasi greenstone). They are metamorphosed under greenschist – amphibolite transitional facies. The present study aims at generating geochemical characteristics of the metadolerites of the basin. Mafic dykes and sills of the basement of the Shillong plateau is of Cretaceous age and excluded from the present study. Geochemically, metadolerites are subalkaline and tholeiitic in nature and emplaced in continental setting. Geochemical data, mantle normalized spidergram and chondrite normalized REE patterns suggest that they are genetically related and probably derived from the same parental source magma undergoing shallow level fractionation.Keywords: Shillong Plateau, Shillong basin, Dolerite dykes and sills, Geochemistry
