The structure and sequence of geological events in the Basement Complex of the Ibadan area,Western Nigeria |
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| Authors: | Kevin Burke SJ Freeth Norman K Grant |
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| Institution: | 1. Department of Geological Sciences, State University of New York, Albany, N.Y. U.S.A.;2. Department of Geology and Oceanography, University College of Swansea Wales UK;3. Department of Geology, Oberlin College, Oberlin, Ohio U.S.A. |
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| Abstract: | The Basement Complex in Western Nigeria in general, and in the Ibadan area in particular, is composed primarily of a banded gneiss in which hornblende-biotite rich bands alternate with quartz-oligoclase rich bands. The banded gneiss, which originated as part of a sedimentary sequence, contains large lenses of granite gneiss and thin intercolated layers of quartzite and amphibolite.Two distinct major structural events can be clearly identified in the early geological history of the Ibadan area. Detailed field studies suggest that the formation of the Ibadan Granite Gneiss, which had yielded an Eburnean Rb-Sr isochron age, was associated with the later of these events. Five phases of dyke or vein formation, two of which pre-date the formation of the Granite Gneiss, have also been identified giving an overall sequence of geological events the first of which may correspond to the beginning of the Liberian orogeny, around 3000 m.y. ago, and the last of which reflects the waning of the Pan-African thermo-tectonic event about 500 m.y. ago. |
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