Tectonophysics_Regional Gravity Study Across WCARS
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Tectonophysics Volume 143, Issues 1 – 3, 15 November 1987, Pages 141 – 159 Continental Rifts-Principal and Regional Ch aracteristics A regional gravity study of the WestAfricanriftsystem in Nigeria and Cameroon and its tectonic interpretation J.D. Fairhead, C.S. Okereke ∗ Department of Earth Sciences, The University of Leeds, Leeds LS2 9JT Great Britain Received 1 February 1985. Accepted 14 October 1986. Available online 9 April 2003. Abstract This study brings together existing and new gravity data to investigate the nature and cause of the Bouguer gravity field associated with the Cretaceous WestAfricanriftsystem in Nigeria and Cameroon. The new gravity measurements include data collected over the basement area between the Benue Trough and the Cameroon border and fill an important gap in the gravity coverage. After removal of the long wavelength negative anomaly from the observed gravity field the remaining positive gravity anomaly, associated with theriftsystem, is interpreted in terms of two and three dimensional crustal models. These models are constrained by crustal thicknesses derived from a seismic refraction study carried out across and to the south of the Yola rift. The results of simple three dimensional gravity modelling indicate the crust beneath the lower and middle Benue is approximately 20 km thick while beneath the Gongola rift the crust is approximately 25 km thick relative to a normal crustal thickness of 34 km away from the rift. Assuming the thinned crust associated with the riftsystem is the result of simple lithospheric stretching, then the maximum possible crustal extensions of 95, 65 and 55 km have taken place perpendicular to the Benu e, Gongola and Yola rifts respectively. These crustal extensions do not necessarily reflect the total crustal movement affecting these rifts since the Benue and Yola rifts have been subjected to varying amounts of shear displacement during the Cretaceous and early Tertiary times. Crustal extension estimates across the WestAfricanriftsystem could be as much as four times greater than the published extension estimates across the East Africanriftsystem. These riftsystems have the same plate tectonic setting being the failed third arms of successful
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Transcript of Tectonophysics_Regional Gravity Study Across WCARS
7/28/2019 Tectonophysics_Regional Gravity Study Across WCARS
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Tectonophysics
Volume 143, Issues 1 – 3, 15 November 1987, Pages 141 – 159
Continental Rifts-Principal and Regional Characteristics
A regional gravity study of the WestAfricanriftsystem in Nigeria and Cameroon and its
tectonic interpretation
J.D. Fairhead,
C.S. Okereke∗ Department of Earth Sciences, The University of Leeds, Leeds LS2 9JT Great Britain
Received 1 February 1985. Accepted 14 October 1986. Available online 9 April 2003.
Abstract
This study brings together existing and new gravity data to investigate the nature and cause of
the Bouguer gravity field associated with the Cretaceous WestAfricanriftsystem in Nigeria and
Cameroon. The new gravity measurements include data collected over the basement area between the Benue Trough and the Cameroon border and fill an important gap in the gravity
coverage. After removal of the long wavelength negative anomaly from the observed gravity
field the remaining positive gravity anomaly, associated with theriftsystem, is interpreted in
terms of two and three dimensional crustal models. These models are constrained by crustal
thicknesses derived from a seismic refraction study carried out across and to the south of the
Yola rift. The results of simple three dimensional gravity modelling indicate the crust beneath
the lower and middle Benue is approximately 20 km thick while beneath the Gongola rift the
crust is approximately 25 km thick relative to a normal crustal thickness of 34 km away from
the rift. Assuming the thinned crust associated with the riftsystem is the result of simple
lithospheric stretching, then the maximum possible crustal extensions of 95, 65 and 55 km havetaken place perpendicular to the Benue, Gongola and Yola rifts respectively. These crustal
extensions do not necessarily reflect the total crustal movement affecting these rifts since the
Benue and Yola rifts have been subjected to varying amounts of shear displacement during the
Cretaceous and early Tertiary times.
Crustal extension estimates across the WestAfricanriftsystem could be as much as four times
greater than the published extension estimates across the East Africanriftsystem.
These riftsystems have the same plate tectonic setting being the failed third arms of successful
7/28/2019 Tectonophysics_Regional Gravity Study Across WCARS
http://slidepdf.com/reader/full/tectonophysicsregional-gravity-study-across-wcars 2/2
triple junctions and are the result of extensional and shear tectonics. The differences in crustal
extension and the resulting isostatic response of the lithosphere beneath these rifts can explain
why the WestAfricanriftsystem has been associated with subsidence processes throughout its
development whereas the East Africanriftsystem in Northeast Africa has been strongly affected
by uplift.
∗ Present adress: Department of Geology, University of Calabar, Calabar (Nigeria).
Copyright © 1987 Published by Elsevier B.V.
