The Nigerian Basemen complex is characterized by both geologic and tectonic structures. Analyses of the structures observed in all the locations visited were carried out.
These occurred mostly as intrusion of concordant and discordant nature; as foliations, xenoliths, vein and dykes.
These are repeated or penetrative planar features in rocks which may be defined by fabric, compositional layering or pervasive fracture. They are the alignment of sheet like minerals such as mica, biotite, muscovite, etc. They were observed at locations 1,4,6,7,11 12 and 13.
From location 13, the following are the 1st readings for the trend of the foliations.
N60, N59, N61, N52, N65, N70, N54, N53, N65, N75
Table 5: Frequency table of trend of foliations at location 13.
Figure: Rose diagram of the trends of foliations at location 13
From the figure above, the unimodal pattern depicts a deltaic environment. The materials must have come from the NE direction and deposited in SW direction. This indicates that the dip direction of the common structures of the northcentral Nigeria Basement complex have N-S trend and a major Norheast-dipping.
These are fragments of rock distinct from rocks in which it is enclosed. They are also foreign rock inclusions a rock. They were observed at locations 10 and 11.
From location 11, the following are the 1st reading of the trends of xenoliths.
N6, N11, N152, N25, N21, N16, N29, N9, N170, N175, N17, N12, N8, N134, N175, N34, N149, N165, N175, N180.
Table 6: The frequency table of trends of xenoliths at location 11.
Figure: Rose diagram of the trends of xenoliths at location 13.
From the figure above, the rose diagram shows the graphic method of the paleocument analysis of the studied area. The Bimodal-Bipolar pattern depicts a tidal environment. The materials must have come from NE, SE directions depositing them in NW SW directions.
These are tabular discordant intrusive structures that cut across the basement discordantly. They occur as ring dyke of rhyolite composition as encountered at location 2. others as diorite dyke as encountered at locations 3,4 and 8.
These are structures in rocks as a result of series of tectonic or orogenic events. The tectonic structures encountered in the studied area are described below.
These are factures in geologic units along which movement has taken place. They were encountered at location 1,3 and 11. These faults are more of strike-slip faults observed here have a major trend of N-S direction.
These are fractures on rocks along which essentially no displacement has occurred. They were observed at almost or more than half of the locations visited. They were encountered at location 2,3,4,7,11,12 and 13. The joints at locations 2 and 3 are cooling joints of different directions, formed during the cooling of the magma. The joints at location 4 are vertical joints.
From location 2, the following are the 1st reading of the trends of the cooling joints.
N122, N146, N49, N160, N164, N143, N149, N112, N110, N141, N143, N104, N113, N164, N142, N119, N155, N135 N110, N105.
Table 7: The frequency table of trends of cooling joints at location 3.
Figure: Rose diagram of the trends of the cooling joints at location 3.
These are evidence of compressive tectonism. They are bends in rocks produced when rocks are in a plastic condition. They were observed at locations 6,7 and 12. the folds encountered are mainly phygmatic folds.