Tectonic Settings and Petrogenesis of Pan-African S-Type Granitoids in Anka Schist Belt, NW, Nigeria

Y S Agunleti ,Najime T

doi:10.7176/jnsr/10-2-08

Abstract

Research into geotectonic settings of the Anka schist belt was regionally carried out by (Holt, 1982) stating that there is no evidence of significant partial melting or metasomatism. This research uses chemical data of some Pan-African granitoids within the Anka schist belt to explain the tectonic setting and petrogenesis of the S-type granitoids intruding the metasediments within the Anka schist belt. Twenty-five (25) representative samples of granitoids was analyzed for major oxides and trace elements composition. Results obtained from the chemical data was used to plot various classification diagrams. The granitoids in the study area plots within the orogenic class and the use of trace element discrimination diagrams as a means of fingerprinting the tectonic environments revealed that the granitoids ranges from syn-collision to late orogenic field. The granitoids which plotted in the syn-collision field is a characteristic of chemical affinity of syn-collision peraluminous granites with highly fractionated volcanic-arc magmas. The petrogenesis of the S-type granitoids in the study area are greywacke sourced which is largely metagreywacke and metapelitic sourced during partial melting. Keywords: Granitoids, Pan-African, S-type, Metasediments, Partial melting DOI : 10.7176/JNSR/10-2-08 Publication date: January 31 st 2020

Highlights

A summary of work on the Birnin Gwari, Maru and Anka belts was carried out by Ajibade (1980), Egbuniwe (1982) and Holt (1982) respectively and presented in (Fitches et al, 1987)
The formation of the granitoids with the use of trace element discrimination diagrams as a means of fingerprinting the tectonic environments were considered and the granitoids plotted in the syn-collision volcanic arc granite field after (Pearce et al, 1984) which is consistent with the tectonomagmatic setting
The petrogenesis of the S-type granitoids in the study area are greywacke sourced from www.iiste.org the plot of Rb/Sr vs. Rb/Ba after (Dahlquist et al, 2007) and Molar CaO/FeOt + MgO vs. Al2O3/ FeOt + MgO after (Altherr et al, 2000) further confirmed that the greywacke is largely metagreywacke and metapelitic sourced during partial melting

Summary

Introduction

A summary of work on the Birnin Gwari, Maru and Anka belts was carried out by Ajibade (1980), Egbuniwe (1982) and Holt (1982) respectively and presented in (Fitches et al, 1987) This summary provides data on sedimentation and tectonics; chemical aspects of volcanic rocks and minor intrusions intimately associated with the metasedimentary rocks; chemical characteristics of the Pan-African plutons cutting the schist belts. From the work of (Holt, 1982), the only pluton known definitely to precede the main deformation is the Gusau granite gneiss www.iiste.org that separates the Maru Belt from the Gusau Migmatites of the basement He stated that the plutons individually and collectively follow a calc-alkaline trend on an AFM diagram and excepting the quartz syenites, are calc-alkaline to alkaline on an alkalinity index diagram and that all the plutons fall within the I-type characteristics. This study concentrated on the use of major oxide, trace elements and rare earth elements geochemistry to determine the magmatic evolution and petrogenetic characteristics the granitoids in the part of Anka schist belt

Methods

Results

Discussion

Conclusion