GRAVITY CHARACTERISTICS OF THE PAN-AFRICAN OROGEN IN GHANA, TOGO AND BENIN (WEST-AFRICA)

In the area of study, 4718 gravity data have been processed. Distribut ion of the resulting anomalies confirms the continuity towards the sou th of the three characteristic gravity domains already identified nort h of the parallel 9 degrees N. Positive anomaly belts underline the pr esence of magmatic rocks in the foreland of the chain. The tectonic ov erload characterizing its external zone is mirrored by a very strong o vercompensation. A main gradient zone (the regional gradient) is super imposed on a suture zone of allochtonous basic massifs. The internal z one is characterized by a very important undercompensation connected w ith heavy deep structures. Numerous gravity discontinuities line the t hree previous sets (foreland, external and internal zones), revealing the great structural complexity of the region. Nevertheless this compl exity is frequently concealed or attenuated by smoothing and offset ph enomena which are expressed through more regular anomalies and profile s. The present study strengthens the hypothesis of a continental colli sion chain for the Dahomeyides and emphasizes the hypotheses of micro- continent aggregation together with a progressive rise of the southern part of the studied sector during the Pan-African tectogenesis. (C) 1 997 Elsevier Science Limited.