Structural Geometry of Pan-African Gneiss in Osara, North Central Nigeria

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Author(s) Udinmwen, Efosa | Ayuba, Rufai | Oden, Michael I
Pages 822-831
Volume 2
Issue 11
Date November, 2013, 2013
Keywords pan-African, Gneiss, Osara, Orogeny, Joints

The rocks of Osara area are non-migmatitic, semi-flat-lying gneisses and older porphyritic granites though surrounded by older migmatites and granite gneiss, the distinct structural pattern displayed by this non-mgmatitic gneisses strongly suggest this rock which occupies a small part of the area to be of Pan-African origin. The structures of gneisses in Osara area were analyzed to ascertain the structural geometry of the rock as well as the Pan-African tectonics/stress system which operated in the area. Results show that foliations, lineations, joints, folds, mineral veins and faulting all occurred in the area. The most dominant structural trend/orientation in this area is the NW-SE and N-S directions, while the NE-SW and E-W directions were available but minimal. The mineral veins grew in the least available extension (ac) fractures showing that they took advantage of the existing (E-W trending) fractures parallel to σ1 direction (maximum compressive stress direction), faults were initiated and propagated along tensile (bc) fractures (N-S trending) while folds has axis parallel to the N-S direction, these show that N-S direction experienced the least compression (σ3 direction) during the orogeny. Lineations were mostly parallel to foliations and these together with joints have a similar geometry where NW-SE and N-S orientations prevailed. The prevalence of NW-SE trending structures in this area is as a result of the high temperature/pressure distribution. In structural analysis/interpretation of any Pan-African region, the distribution (temperature and pressure) and rock type/structure should be considered because the dominant structural trends produced by the Pan-African orogeny tends to vary with respect to temperature, pressure and the rock type/structure being studied.

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