GRAVITY SURVEY OF SHIRA YOUNGER GRANITE- RING COMPLEX OF NORTHERN NIGERIA
GRAVITY SURVEY OF SHIRA YOUNGER GRANITE- RING COMPLEX OF NORTHERN NIGERIA
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Date
1981-09
Authors
OGBUOJI, ONYIBA NNACHI
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Abstract
The gravity survey over the Shira Younger Granite Ring
Complex is aimed at investigating the subsurface structure
of the ring complex whose three main rock types are
arfvedsonite granite, biotite granite and syenite.
Density determinations of the rock samples in the area
gave values of 2.62 x 103 kg m3 for arfvedsonite granite,
2.58 x 10 kg m-3 for biotite granite- and 2.66 x 103 kg m-3
for syenite.
A pear-shaped positive Bouguer anomaly striking S W
was observed over the arfvedsonite granite and biotite
granite which forms the northern part of the complex.
While at the southern section, over the syenite, the Bouguer
anomaly is predominantly negative with an E - W trend. The
residual gravity anomalies of the northern and the southern
sections are of amplitudes + 70 g.u. and - 80 g.u.
respectively. These suggest that the northern section of
the complex had been intruded at depth by a high density
material possibly basalt, possibly after the formation of
the complex.
The subsurface structure of the Shira Younger
Granite Ring Complex consists of three layers at depth.
The rock type that is least exposed arfvedsonite
granite is the most deeply seated, while the highly
exposed, most dense-, syenitic massifs is the least in
subsurface thickness and is else the uppermost layer.
One of the profiles interpreted indicate that the
syenitic massif extends from the ground surface to a
depth of 1.0 km. This is underlain by the biotite
granite mass whose thickness is 2.0 km. which is in
turn underlain by the arfvedsonite granite body located
at a depth of 2.5 km. to 4.0 km.
Description
Thesis submitted to the Ahmadu Bello University
Zaria in partial fulfilment of the requirements
for the award of the degree of
MASTER OF SCIENCE IN
APPLIED GEOPHYSICS.
Department Physics
Ahmadu Bello University,
Zaria - Nigeria.
Keywords
GRAVITY SURVEY,, SHIRA YOUNGER GRANITE- RING COMPLEX,, NORTHERN NIGERIA,