Structural and Petrographic Study of Crystalline Rocks in Part Of Oban Massif, SouthEastern Nigeria

Abstract

The study aims at differentiating lithologic units, general structural trends and orogenic implications of crystalline rocks within part of Oban Massif, Southeastern Nigeria. Field study involve geological mapping, rock description and structural measurement, while laboratory analysis covered photomicrograph. Field observation and microscopic analysis reveal five petrological units; gneisses, schists, granodiorite, pegmatite and quartz veins. The rocks are generally siliceous and quartzo-feldspathic. The schist show foliation planes trending majorly in the NE-SW direction. The gneisses were highly fractured, indicative of a polyphase deformation. Structural elements such as joints, fractures, foliations and veins show series of deformational episodes that affected the area. Rose diagram plot for these structures show the NE-SW direction indicative of the Pan-African orogeny (600±150 Ma) and interpreted as the most recent event affecting the area. NW and NE trending joints are consideredto be tectonic in origin based on their alignments with major structures of the area. Furthermore, the structures also showed weak NW-SE and E-W trends, an imprint of older (Kibaran orogeny) deformational episodes.