Study of Origin, Geology and Geochemical Classification of the Granitoids of Imori Area, North Central Nigeria

Abstract

Two distinct generationsof granitiods in terms of space and time were identified in the Imori fields of north central Nigeria. The first generation is the Older Pan-Africa calc-alkaline granite suites(OPACG)which comprises the migmatite-gneiss and the porphyritic hornblende-biotite granite.The second group is the Younger Mesozoic alkali granite suites (YMAG).This comprises the rhyolite, biotite granite and arfvedsonite granite. The OPACGsuites are characterized by depletion in SiO2ranging from 63.30 wt % -68.38 wt % as compared to the YMAGsuites which range from 70.41 wt % -79.14 wt %. In addition, the OPACGsuites are characterized by higher concentrations of MgO, fe2O3, Al2O3, TiO2, CaO and Sr as compared to the YMAGsuites. The YMAGsuites are characterized by an excess of total alkaloids (Na2O +K2O), Cr, Nb, W, Ta, and lower concentrations of ferromagnesian minerals. These characteristic indicates that the OPACGsuites are generated from deep seated crustal levels rocks with the possibility of mantle materials. The YMAGsuites were originated from partial melting of crustal sialic materials. Both thetrace element patterns of the OPACG suites and the YMAGsuites indicate that each suiteis co-magmatic.