The Geology and Petrography of Precambrian Basement Rocks of Gbunchu and Environs in Akwanga Local Government Area, Nassarawa State, North-Central Nigeria.

ABSTRACT

The study area is located within the north-central Nigeria in Akwanga town, Nassarawa state. It lies between Latitudes 8°55'N to 9°00'N and Longitudes 8°25'E to 8°30'E. It is underlain by crystalline rocks of the Basement Complex “sensu stricto”, which comprises of migmatitic banded gneiss, biotite gneiss and gneissic granite. Based on the field characteristics and petrographic studies the area is believed to have attained a very high regional metamorphism and likewise has undergone polyphase tectono-metamorphic events (more than one deformational episode). The variation in the foliation trends from NNE-SSW to NNW-SSE orientation accounts for polyphase metamorphism in the area. The dominant NNE/SSW foliation trends are imprints of the Pan-African thermotectonic event while the NNW/SSE foliation trends represent imprints of older events than the Pan-African orogeny (Liberian, 3000-2400Ma, Eburnean, 2400-1600Ma and Kiberan, 1600-900Ma). This localized foliation trend are relict structures suggesting that the study area may not have been affected by the widespread Pan-African orogeny which impacted the characteristic NNE/SSW foliation trends. The gneissic granite is believed to have been emplaced later than the migmatitic banded gneiss and biotite gneiss in the area. The ages of the crystalline rocks within the study area are all Pan-African. Vegetation and hydrogeology of the area is influenced by the weathered crystalline rocks. The crystalline rocks of the study area also serve as good source of building and construction materials and other important raw materials in industries.