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The seismicity of eastern an southern Africa
Geoexploration,
20 (1982)
207-208
207
Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands Abstructs* GRAVITY
FIELD OF THE BENUE TROUGH,
NIGERIA
C.I. ADIGHIJE and 0. OFREY Department
of Geology, University of Ibadan, Ibadan {Nigeriu)
The Benue Trough is of considerable interest as a possible Cretaceous intracontinental “failed” rift. In order to further investigate its subsurface structure and sediment thickness 600 gravity stations were established in the Lower and Middle Benue Trough. These were compiled with existing data to form a new Bouguer gravity map of the trough. Bouguer anomalies range from -60 to +30 mgal, the positive anomalies being confined only to a narrow belt om the floor of the Lower Benue Trough. The predominant gravity high across the whole trough is attributed to crustal thinning. Four section models show slight crustal thickening from 31.4 km to 30.6 km, increased thickness of the elevated crust-mantle interface from 1.5 km to 3.0 km, and narrowing of the elevated interface from 170 km to 70 km width, all from south to north. The axial negative anomaly observed in the Upper Benue is attributed to sedimentary fill 6000 m thick. The flanking negative residual anomalies in the Middle and Lower Benue are considered to represent accumulations of up to 5000 m of post-deformational sediments in the marginal basins. The axial positive anomaly is associated with a dense anomalous body that increases in width and thickness from north to south in the trough. The gravity models explain some salient features associated with the evolution of the rift. These are discussed in the paper, as are parallels and contrasts with the present-day Ethiopian rift and the Red Sea.
THE SEISM~CITY
OF EASTER
AN SOUTHERN
AFRICA
J.D. FAKRHEAD Department
of Earth Sciences,
University of Leeds, Leeds (Great Britain)
This paper is a review, relating the seismicity of eastern and southern Africa to the basement geology and tectonics. The state of stress within this part of the African plate is investigated using new focal mechanism data.
*From the Proceedings of the 26th International Geological Congress, Paris.
0016-71~2/82/0000-0~00/$02.7~
o 1982 Else&r Scientific Publishing Company
20 (1982)
207-208
207
Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands Abstructs* GRAVITY
FIELD OF THE BENUE TROUGH,
NIGERIA
C.I. ADIGHIJE and 0. OFREY Department
of Geology, University of Ibadan, Ibadan {Nigeriu)
The Benue Trough is of considerable interest as a possible Cretaceous intracontinental “failed” rift. In order to further investigate its subsurface structure and sediment thickness 600 gravity stations were established in the Lower and Middle Benue Trough. These were compiled with existing data to form a new Bouguer gravity map of the trough. Bouguer anomalies range from -60 to +30 mgal, the positive anomalies being confined only to a narrow belt om the floor of the Lower Benue Trough. The predominant gravity high across the whole trough is attributed to crustal thinning. Four section models show slight crustal thickening from 31.4 km to 30.6 km, increased thickness of the elevated crust-mantle interface from 1.5 km to 3.0 km, and narrowing of the elevated interface from 170 km to 70 km width, all from south to north. The axial negative anomaly observed in the Upper Benue is attributed to sedimentary fill 6000 m thick. The flanking negative residual anomalies in the Middle and Lower Benue are considered to represent accumulations of up to 5000 m of post-deformational sediments in the marginal basins. The axial positive anomaly is associated with a dense anomalous body that increases in width and thickness from north to south in the trough. The gravity models explain some salient features associated with the evolution of the rift. These are discussed in the paper, as are parallels and contrasts with the present-day Ethiopian rift and the Red Sea.
THE SEISM~CITY
OF EASTER
AN SOUTHERN
AFRICA
J.D. FAKRHEAD Department
of Earth Sciences,
University of Leeds, Leeds (Great Britain)
This paper is a review, relating the seismicity of eastern and southern Africa to the basement geology and tectonics. The state of stress within this part of the African plate is investigated using new focal mechanism data.
*From the Proceedings of the 26th International Geological Congress, Paris.
0016-71~2/82/0000-0~00/$02.7~
o 1982 Else&r Scientific Publishing Company