A magmatic failed rift beneath the Gongola arm of the upper Benue trough, Nigeria?

A magnetic anomaly map of the Gongola arm of the upper Benue trough was com piled from existing half-degree sheets of the upper Benue trough. The map i s dominated by an elongated NE-SW magnetic low anomaly that stretches over a 100 km distance and has an average width of about 20 km. A combination of Werner deconvolution and forward modeling techniques on selected profiles across the major NE-SW anomaly lead to the conclusion that the anomaly may be caused by predominantly mafic rocks at depths of between 6 and 10 km, we ll below the base of the sediments, which are generally not more than 4.5 k m thick. The presence of large and continuous bodies of mafic rocks indicat ed by these results suggests that the area is an old rift, affected by the activity of a mantle plume that gave rise to the mafic intrusions, which di d not reach the surface but remained within the basement rocks. (C) 2001 El sevier Science Ltd. All rights reserved.