P-T conditions of Pan-African orogeny in southeastern Nigeria

Abstract Different rock types from the area northeast of Obudu, southeastern Nigeria were investigated in order to place constraints on their metamorphic conditions. Detailed petrographic studies indicate four main rock groups in the studied area, namely migmatitic gneiss, migmatitic schist, granite gneiss and a minor amount of amphibolite, metagabbro and dolerite. The chemistry of minerals in these rocks is used to estimate metamorphic pressure and temperature (P-T) using appropriate geothermometers and geobarometers. The estimated temperature for migmatitic gneiss of the area is ∼600–625 °C and 600–650 °C for migmatitic schist; the pressure is ∼ 8 kbar. For amphibolite the temperature is ∼600–700 °C and pressure is 8–12 kbar. The estimated pressures and temperatures for the northeast Obudu rocks correspond to upper amphibolite to lower granulite facies metamorphism. The metamorphism occurred due to continent-continent collision during the Pan-African orogeny, most likely during the D1 deformational phase of the area. The recorded high pressures possibly resulted from crustal thickening in the area. P-T conditions for Pan-African orogeny in northeast Obudu area are in good agreement with P-T estimations for the Pan-African event in adjacent areas