Some previous jobs done had confirmed the dominance of the Basement complex underlying the entire area of Northern Nigeria and some parts of Southeastern and southwestern Nigeria. The Basement geology of Nigeria covers most areas of the Northcentral zone, south western zone, south eastern zone, North eastern zone, south southeastern zone (the oban massif) where they are seen to be well pounced.
The Basement complexes are composed of mainly igneous and metamorphic rocks, including the older rocks of Precambrian age and the late proterozoic meta-sediments most of which are of high metamorphic grade like paragenesis, basic and calcareous schist, marble and quarzites, orthognesis and the early Eburnean granites. In the west, the rock types and sequence of events recognized can be correlated with the Buenu and Togo formation in Ghana, Togo and Dahomey.
The Phanisian chain in the Ahagar having been acted upon by two tectono-metamorphic cycles and series of consequent metamorphism, migmatization and granitization, the original rock materials of the Basement have been deeply modified yielding the complex nature, relict relicts are believed to be of an older supracrustal cover probably of Birriamian age, and are returned as older meta-sediments for dear differentiation from the late proterozoic supracrustal sediments referred to younger meta-sediments.
FURTHER STUDY ON REGIONAL GEOLOGY
These younger meta-sediments. These younger meta-referred to younger meta-sediments. These younger meta-sediments which form well defined approximately North-South trending belts extensively developed in the North west are remnants of once an extensive supracrustal cover.
The interpretation on the evolution of the Nigerian Basement and the variable nature of the pan-African events (McCurry 1971 and Grant 1970), prove a considerable variation on the younger meta-sediments. These range from psammitic to politic sediments of low facies and interbedded lavas.
They have been steeply folded along with the Basement complex during pan-African Orogeny, so that they now occur in synclinorial trough in a sea granitic material resembling the gemstone-mignatite association of cratonic regions (Wright and McCurry 1970).
During the Pan-African Orogenic cycle events, an intrusion of older granitic series have been recorded. And with more complicated folding of the older meta-sediments in constrast to the structures of the younger belt, yielding a complex deformational history. The earliest of these intrusions appeared to be basic and intermediate intrusive represented by a small irregular body of quartz and pyrozene, diorite and gabbro.
In the Northwest such basic rocks later witness acid rock intrusion forming acid-basic complex. Granitization on its own later culminated in the intrusion of a diverse and wide spread suite of syn to late tectonic, granites, granodiorite and syenites. And these granitisation on an extensive scale greatly modified earlier rocks and resulted in a wide spread migmatitic and granitic rock materials.
Table Summarized succession table showing the locations visited and its various rock types.
|10||Pure migmatitic terrain|
|13||Porphyroblastic granite gneiss|