Abstract
Syn-collisional granite in the northern part of the Birnin Gwari schist belt consists dominantly of granite and lesser granodiorite and quartzolite. Petrographic and ge¬ochemical data revealed three granite groups: the biotite-hornblende granite (quartzolite - BHG); the biotite granite (BG) and the biotite-muscovite granite (BMG). The rocks generally have calc-alkaline and high-K calc-alkaline affinities, and calc-alkalic to alkali-calcic, peraluminous and ferroan and magnesian geochemistry. They are characterized by LILE enrichment, high LREE fractionation factor [(La/Yb) (6.74 to 45.14] with weak to moderate negative Eu (Eu/Eu* = 0.38 to 0.62) and strong negative Nb, P and Ti anomalies. Variation in the behavior of lithophile elements (Ba, Sr and Rb) revealed diverse granite trend such as “high and low Ba-Srâ€; “normalâ€, “anomalous†“strongly differentiated†and “granodiorite and quartz diorite†granite. Their display of similar trace elements and REE patterns suggest they are cogenetic. Major and trace element data indicate differentiation of a mafic magma and partial melting of crustal components inherited from shale-greywacke and quartzose sedimentary protoliths in volcanic arc and post collisional settings. The field and geochemical characteristics of this granite suggest that they are similar to other granites in schist belts in other parts of Nigeria, forming the lateral continuation of the same Pan-African magmatic belt.  Â
Highlights
Syn-collision granites in and around Birnin Gwari area constitute one of the three major rock units of the Precambrian Basement Complex rocks north of Birnin Gwari schist belt
Little or no work has been done on the granitoids in this part of the Birnin Gwari schist belt
Petrographic and geochemical data have revealed three granitoids groups in the Biirnin Gwari granitoids: the biotite-hornblende granite and quartzolite (BHG), the biotite granite (BG) and the biotite ± muscovite granite (BMG), with plagioclase, hornblende and biotite fractionation playing an important role during continuous fractional crystallization process
Summary
Syn-collision granites in and around Birnin Gwari area constitute one of the three major rock units of the Precambrian Basement Complex rocks north of Birnin Gwari schist belt. Radiometric age measurement of Rb – Sr data from Kusheriki granite emplaced across the gneissic envelope gives an age of 500 + 4 Ma. which suggests Pan-African deformation and emplacement of the region (Ajibade et al, 1979; 2008) They described a complex structural sequence from parts of the neighbouring Birnin-Gwari Schist and Ushama Schist Formations and identified four deformation episodes that have affected the rocks in these areas and later define the Zungeru Mylonites. They confirmed the presence of two types of migmatites and gneisses which are believed to belong to two different ages. Major, trace and rare earth elements (REE) data on eight relatively unknown granitic plutons and four host rock (granite gneiss) have been used to assess their petrogenetic evolution and tectonic setting
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