GLOBAL JOURNAL OF GEOLOGICAL SCIENCES VOL, 9, NO.2, 2011 253-263 253 COPYRIGHT© BACHUDO SCIENCE CO. LTD PRINTED IN NIGERIA. ISSN 1596-6798 www.globaljournalseries.com , Email:
[email protected] SOME GEOCHEMICAL CONSIDERATIONS IN THE PETROGENESIS OF MADAGALI GRANITOIDS, NORTHEASTERN NIGERIA SAIDU BABA (Received 30 November 2010; Revision Accepted 10 February 2011) ABSTRACT Major and trace element geochemical data on granitoids of Madagali area of northeastern Nigeria show a series that ranges from K-calcalkaline, through granodiorite-monzogranite to granite. They are characterized as mildly peraluminous to metaluminous and I-type based on alumina saturation index (ASI). Trace element contents preclude the possibility of entire mantle origin and indicate significant crustal involvement in the evolution of the granitoids. The enrichment in LREE ( La, Ce and, Nd), depletion in HREE (Ho, Er, Yb and Lu) and a pronounced negative Eu anomaly with (La/Yb) N suggest that the granitoids must have evolved by partial fractionation or partial melting of the pre-existing crust in which plagioclase feldspar was retained. Furthermore, the enrichments in some large-ion- lithophile elements (LILE) such as Rb, Ba, Th and K and depletion in some high field strength (HFS) elements such as Nb, P, and Ti as well as some transitional elements Cr and Ni are supportive of crustal involvement in their genesis. KEY WORDS : Madagali, Nigeria, Granitoids, Geochemical considerations, Petrogenesis. INTRODUCTION (1986) concluded that the Pan-African granitoids in The study area is the northeastern tip of the central Nigeria were derived by partial melting of the Nigerian Basement complex, separated from the country rocks (schists and gneisses), while Ezepue and southern part (Oban-Obudu Massif) by the Upper Benue Odigi (1993) showed that the various components of Trough.