DUCTILE SHEARING AND REMOBILIZATION OF PORPHYRITIC GRANITE IN KORO-EGBE AREA, SOUTHWESTERN NIGERIA.
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Date
2013
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Journal ISSN
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Publisher
Faculty of Pure and Applied Sciences, LAUTECH, Printed in Nigeria
Abstract
Penetrative metamorphic tectonite fabrics, folds, and shear zones constitute the main structural elements in Koro-
Egbe area. Results of field mapping, which was used to constrain the shear zone, revealed the nature of the fabrics
in the grey gneiss, schist, meta-basites and the Pan African granites in the area. The development of penetrative
fabrics in the large-scale sheeted rocks defines the first deformation episode, D1. The second deformation episode
D2, is revealed in the horizontal asymmetric folds (Koro-Egbe folds), while a major shear-zone developeded
during a post-folding phase defines the D3 event.
Within the shear-zone, bodies of porphyritic biotite granite of Pan African age (600±150Ma) were strongly
tectonised with a north-easterly steeply-dipping foliation. Outside the shear zone, the porphyritic granite is
relatively undeformed, preserving strong igneous textures. Smaller bodies of fine-medium grained biotite granite
occur within the deformed porphyritic bodies in the shearzone. It is consideredthat the petrogenesis of these
smaller bodies is strongly linked with the shearing under a high geothermal condition.
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Keywords
DUCTILE SHEARING, REMOBILIZATION, PORPHYRITIC GRANITE, KORO-EGBE AREA, SOUTHWESTERN NIGERIA