GRAVITY INVESTIGATIONS IN THE MIDDLE NIGER BASIN AREA, NIGERIA
GRAVITY INVESTIGATIONS IN THE MIDDLE NIGER BASIN AREA, NIGERIA
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OJO, Samuel Bakare
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Abstract
Gravity measurements carried out in the Middle Niger Basin area show
that the area is characterised by negative Bouguer anomalies ranging in
value from -67 mgal to +15 mgal. The free-air anomalies are distributed
about a mean value of approximately +5 mgal. which suggests that the area
is approximately compensated. A regional anomaly ranging in value from
about -20 mgal in the sourthern parts of the area to about -20 mgal in the
northern parts of the area is correlated with a gradual thickening of the
crust from the South to the North. Major negative residual anomalies centred
on the basin are explained by the presence of thick Cretaceous sedimentary
rocks in the area. Positive residual anomalies also occur over parts of the
basin and these are attributed to a high-density metamorphic basement, and
to masses which are probably of scirest composition.
From two dimensional modelling based on gravity profiles it is estimated
that the maximum possible thickness of the 6retaceous sediments is generally
of the order of 2km, and is nowhere considered to exceed 2.7 km.
The gravity pattern at the boundaries of the basin indicates that the
contacts at the edges of the basin are probably not faulted. The basin
is therefore thought to be an area of local subsidence.
Description
Thesis submitted to the Ahnadu Bello University
for the degree of Master of Science
Department of Physics
Ahmadu Bello University
Zaria - Nigeria
Keywords
GRAVITY, INVESTIGATIONS, MIDDLE, NIGER, BASIN, AREA,, NIGERIA