The petrology of the North western region of Boki, Bamenda massif, South Eastern Nigeria – E O. Ibegbulam and E. E. Ukwang
The crystalline basement rocks mapped within northwest Boki area (Latitudes 60 151N and 60 301N and Longitudes 80.451E and 90.001E) include migmatitic gneisses, augen gneiss, garnet-mica schist, biotite gneiss, garnetiferous granite, granodiorite, dolerite, basalt and gabbro. The dominant foliation trend in the area is N – S to NNE – SSW with dips in the northwest. This is an indication that the area was affected by the Pan-African thermotectonic events (550 ± 100ma). The average dip value of the foliated rocks is 500. However few foliations trend in the NNW-SSE with dips in the northeast. The garnet–mica schist have well developed schistosity and partly preserved beddings (a synsedimentary deformational structure). The migmatitc gneiss have their gneissose banding modified by shearing and injection of felsic materials consisting of the various cross-cutting quartzo-feldspathic veins, and by contortions resulting from folding. There are fractures in the rocks several of which cut across the foliation trend. The minerals present in the metamorphic rocks which include feldspars + chlorite + garnet + biotite + quartz suggest a sedimentary progenitor. Field observations and other evidence suggest that the gneisses form the basement for the emplacements of basic and granitic rock intrusions. The gneisses and the schist are extensively dissected by a network of crosscutting quartzo-feldspathic vein/vein-lets of various orientations and average widths of about 7cm. The dolerites occur as dismembered lenticular enclaves within the metamorphic rocks. The paragenetic assemblages and structures present in the rocks in the map area suggest that the rocks in the northwest Boki area of Bamenda massif have, at least, experienced high grade amphibolite facies metamorphism with the exception of the largely unmetamorphosed igneous bodies.