A DETAILED GRAVITY SURVEY OF THE MIDDLE BENUE, NIGERIA
A DETAILED GRAVITY SURVEY OF THE MIDDLE BENUE, NIGERIA
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Date
1979-05
Authors
Ajayi, Clement Olatunde
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Abstract
The result of a gravity survey carried out in the
Middle Benue and discussed in this work, in dictate the
existence of aright of normal width (about 40 km),
buried under Cretaceous cover . Thirsts is axially
located between the axial-ridge of the trough end t he
northern boundary of through . The gravity low (about
- 37 to - 15 meals) which occur between the Aldridge and
the southern boundary of t h e trough has a ls so been ascribed
to another rift . The interpretations further suggest t he
existence of buried , deeply - rooted (about 7 intermediate
and local is intrusiveness, whose tops accelerated at
about 200 to 500 m below the ground surface, just beyond t he
present margins of the trough and along the earwax trough retrospectively . The above f acts suggest t h at
the Benue trough did not only originate through refitting
but that it may presently consist
which a re-separated by an Aldridge
Further more , the gravity data suggests that the
Middle Benue can be divided of destructive region
which includes precariously geologically unknown ( and/or
geophysical y ) region . Within t h e four regoins which
contain known structures, the trends and locations of the
structures were confirmed by the gravity data. However,
features such as the trend of the Giza sync-line between
Radarko and Obi and the location of the axis of the Keana
anticline in the project area, as deduced from the residual
gravity map, did not agree with those on the geological
map. The new structures revealed by the gravity data
include a broad anticline about 30 km south' of the River Benue,
which is axially placed within the trough as the Keana anticline
about 30 to 40 km north of the river, and a normal fault which
separates the two axial a n t i c l i n e s . The new structural region
deduced from the gravity data is characterized by low gravity
(values - 20 to 36 meals)and it is a southeast trending zone which
might be a zone in which subsidence is accompanied with block
faulting. Finally, the r e s u l t s of the work also suggest possible
reasons for the geological p e c u l i a r i t i e s of the trough such as the
abnormal width of the trough, the folding of the sediments in the
trough and the apparent lack of surface, indications of rifiting
at the margins of the trough.
The results of a gravity survey carried out in the
Middle Benue and discussed in this work, in abdicate the
existence of Arafat of normal width (about 40 km),
buried under Cretaceous cover. This refit is axial y
located between the axial-ridge of the trough end t he
Northern boundary of the trough. The gravity low (about
- 37 to - 15 mgals) which occur between t h Aldridge and
the southern boundary of the trough has also been ascribed
to another rift . The interpretations further suggest the
assistance of buried , deeply - rooted (about 7 km) intermediate
and local is deconstructionism , whose tops eallocated at
about 200 to 500 m below the ground surface, just beyond the
present margins of the trough and along the axial-ridge
of the trough retrospectively. The above facts suggest that
the Benue trough did not only originate through refitting
but that it may presently consist of two parallelisms
which a respected by an axial ridge.
Further more , the gravity data suggest shat the
Middle benue can be divide-int of divest cultural regions
which includes a previously unknown ( geologically and/or
geophysical y ) region . Within t h e four region which
contain known structures, the trends and locations of the
structures were confirmed by the gravity data. However,
features such as the trend of the Giza syncline between
Radarko and Obi and the location of the axis of the Keana
anticline in the project area, as deduced from the residual
gravity map, did not agree with those on the geological
map. The new structures revealed by the gravity data
include a broad anticline about 30 km south' of the River Benue,
which is axially placed within the trough as the Keana anticline
about 30 to 40 km north of the river, and a normal fault which
separates the two axial anticilline . The new structural region
deduced from the gravity data is characterised by low gravity
(values - 20 to 36 mgals)and it is a southeast trending zone which
might be a zone in which subsidence is accompanied with block
faulting. Finally, the results of the work also suggest possible
reasons for the geological peculiertist of the trough such as the
abnormal width of the trough, the folding of the sediments in the
trough and the apparent lack of surface, indications of rifting
at the margins of the trough.
The results of a gravity survey carried out in the
Middle Benue and discussed in this work, in dedicate the
existence of a rift of normal width (about 40 km),
buried under Cretaceous cover . This rift is axially
located between the axial ridge of the trough end t he
northern boundary of the trough. The gravity low (about
- 37 to - 15 mgals) which occur between t h axial ridge and
the southern boundary of the trough has also been a scribed
to another refit . The interpretation Hesther suggest the
existence of buried , deeply - rooted (about 7 km) intermediate
and local is volcanically rusions , whose tops are located at
about 200 to 500 m below the ground surface, just beyond t he
p r e s e n t margins of t h e trough and along the a x i a l r i d ge
of t h e trough r e s p e c t i v e l y . The above f a c t s suggest t h at
t h e Benue trough did not only o r i g i n a t e through r i f t i ng
but t h a t it may p r e s e n t l y c o n s i s t of two p a r a l l e l r i f ts
which a r e s e p a r a t e d by an a x i a l r i d g e.
F u r t h e r m o r e , the g r a v i t y d a t a s u g g e s t s t h a t t he
Middle benue can be d i v i d e d i n t o f i v e s t r u c t u r a l r e g i o ns
which i n c l u d e s a p r e v i o u s l y unknown ( g e o l o g i c a l l y and/or
g e o p h y s i c a l l y ) r e g i o n . Within t h e four r e g i o n s which
( i)
contain known structures, the trends and locations of the
structures were confirmed by the gravity data. However,
features such as the trend of the Giza syncline between
Radarko and Obi and the location of the axis of the Keana
anticline in the project area, as deduced from the residual
gravity map, did not agree with those on the geological
map. The new structures revealed by the gravity data
include a broad anticline about 30 km south' of the River Benue,
which is axially placed within the trough as the Keana anticline
about 30 to 40 km north of the river, and a normal fault which
separates the two axial a n t i c l i n e s . The new structural region
deduced from the gravity data is characterised by low gravity
(values - 20 to 36 mgals)and it is a southeast trending zone which
might be a zone in which subsidence is accompanied with block
faulting. Finally, the r e s u l t s of the work also suggest possible
reasons for the geological p e c u l i a r i t i e s of the trough such as the
abnormal width of the trough, the folding of the sediments in the
trough and the apparent lack of surface, indications of r i f t i ng
at the margins of the trough.
Description
A Dissertation submitted to theAhmadu Bello U n i v e r s i t y , for t he
degree of Doctor of Philosophy in Applied Geophysics
Zaria, Nigeria
May, 1979
Keywords
DETAILED,, GRAVITY,, SURVEY,