Geochemistry and Petrology of Guguruji Amphibolites from Egbe-Isanlu Schist Belt, Southwestern Nigeria

Geochemistry and petrology of Guguruji amphibolites from Egbe-Isanlu Schist belt, Southwestern Nigeria has been carried out to determine its nature and geochemical characteristics. The petrographic study of some of the samples reveals that mineral composition is uniform in some exposures and varied more in others. The thin sections reveal essentially biotite, hornblende, plagioclase, quartz, actinolite, tremolite, and opaque minerals. The minerals have random orientation of long axes of abundant hornblende and subordinate plagioclase crystals. The amphibolites are characterized by average contents of SiO2 (≤54%), Al2O3 (<15%), MgO (<10%), CaO (13.7%) and generally low total alkali (<2%), P2O5 (0.3%), MnO (<0.3%) and TiO2 (<2%) values. Other chemical parameters such as CaO / Al2O3 (<0.9) and Rb/Sr (<0.13) confirms its ortho-genetic origin. Binary plot of Na2O + K2O versus SiO2 and ternary diagram of Fe2O3– Na2O –MgO suggests that the amphibolites are of a precursor magma of subalkaline/basaltic and tholeiitic petrogenetic affinity. The trace element characterization of the amphibolites implicates within-plate tectonic setting.