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.

Geochemistry of Schists of Northwest Obudu Plateau, Southeastern Nigeria

“…% (Table 2), except the HBS which is relatively depleted in K 2 O with value of 1.52 wt % (Table 2). Analyses using both the CIPW and Niggli norms of the schists of Northwest Obudu Plateau show that they are all quartz normative and have positive quarzzahl values with Niggli al > alk, which is consistent with their metapelitic character (Ekwueme 2003;Ephraim et al, 2008).…”

“…The pioneer work on the petrography and major element geochemistry of northern Obudu was done by Ejimofor et al, (1996). Other detailed study on the adjacent blocks of the Obudu Plateau are those of Orajaka (1971), Beltaro (1962), Ekwueme (1998), Ukaegbu (2003), Ukaegbu and Beka (2007), Ephraim (2005Ephraim ( , 2009, Ephraim et al, (2008), Ukwang (2007), Ekwueme (2010) and Obioha and Ekwueme (2011). However, these works were more generalized and not concentrated on the schists occurrences in the area.…”