Strain analysis and tectonite classification using polymictic metaconglomerates in the Igarra schist belt,southwestern Nigeria

Deformed conglomerates in the Igarra schist belt display contrasting strains between different lithological clast populations. We analysed three different clast populations (pegmatite, metasediment, quartz) across three sites in the Igarra metaconglomerates of Edo state, Nigeria. We calculated finite strain using the R_f/ø method and Flinn graph. Quartz clasts exhibited the least amount of strain, while the pegmatite and metasedimentary clasts had greater strains (pegmatite > metasediment > quartz). The variability in the finite strains gotten from the three sites is controlled by clast composition and probably grain size. The differences in finite strain and maximum elongation direction (λ ₁) in the three sites indicates that the Igarra metaconglomerates was subjected to a heterogenous simple shear deformation which is probably associated with the general transpressional deformation that affected the Pan-African mobile belt considering its (Igarra schist belt) spatial proximity with regional dextral shear zones. Three-dimensional strain analysis in site one indicates a constrictive deformation with the dominance of L tectonites. Spatial analysis of two-dimensional strain suggests a strain gradient where finite strain decreases from north to south.