Structural framework and deformation episodes in the igarra schist belt, southwestern nigeria

Abstract

The structural framework of the Igarra schist belt consists of brittle (mainly fractures) and ductile (foliation, cleavage, folds, lineations, strain markers) structures. The geometry of these structures reveals two major occurrences of transpressional deformation affected the schist belt. These are an older dominantly ductile deformation with NW–SE λ₁ which developed foliations, cleavage, folds, and mineral/stretching lineations deforming only the metasediments and a younger brittle–ductile, E-W tectonic shortening deformation which closed deformations in the Igarra schist belt, deforming both the metasediments and granitoids, producing almost all the brittle structures in the belt. Minor fracture trends which are not associated with any of the major episodes of deformation and E-W transposition foliation in marble and gneisses constitute a relic of an unconfirmed possibly older episode of deformation. Ductile and semi-brittle shear zones in the Igarra schist belt are few and usually occur on small scale (outcrop scale), hence, they do not constitute a major episode of deformation. Mineralizations in the Igarra schist belt are pegmatite and quartz which are emplaced mainly in fractures with industrial minerals like marbles.