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Abstract. - Our aim is to define : -a) Individualization of peripheral bulges with their style (faults or flexures) ; - b) Rythm of uplift punctuated by the development of stepped planation surfaces which indicate periods of tectonic quiescence or at least of a relative stability ; a great number of surveys carried out on the continental shelf brought complementary information on sedimentation (fades, thickness, deposits ages). It is then possible to precise the principal stages ; - c) Working mechanisms with their geophysical implications. The problem stands not only at the Moho layer but also at the level of discontinuity of the base of the lithosphere in contact with the asthenosphere.

Abstract. - From Namibie to Congo, the western african bulge was first uplifted before the Aptian. But major flexuration was emplaced between upper Cretaceous and Pliocene. Angola is well known for his wonderful stepped planation surface : the highest is attribued to late Cretaceous, the intermediary one to Miocene, and the lowest to Pliocene. In Congo and Namibie, the succession of events is significantly different. In Transvaal and Namibie, a giant flexure affects a volcanic serie ending with basalts of lower Jurassic age. Tentatively the Highveld planation surface cutting across kimberlite pipes is attribued to late Cretaceous or Paleocene. The lowest step (Lowveld) appears related to the neogene accumulation. An intermediary surface cuts across the crystalline northern scarp and the top of the Lebombo Ridge. The best studied area of the Western Ghats consists of subhorizontal traps of paleocene age. Neither upper post-trappean planation surface, neither important lower steps were identified. The dissymetric bulge is supported by a thickened crust. Proved post-trappean faults are restricted to the shelf. But the thickest neogene sediments are chiefly tilted oceanwards.

Conclusion : the mechanisms of uplift. In the most cases (excepting northern Ghats and perhaps south african bulge), the mechanisms of uplift will be sought into light infracrustal roots, proceeding either directly from heating, either from transformation of ec/ogites into gabbros. The models must take into account the rythm of uplift, as registered by geomorphological-geological research. Some mechanisms of uplift of the bulges have been discussed. M.F. André suggests that asthenosphere is pushed beneath the continental bulge by subsidence of the dead cooling Labrador dorsal. Y. Battiau-Queney invokes the excess of lithostatic preasure in the new oceanic lithosphere respect to the continental one. P. Birot tests a model where the light roots of the bulges result from the thermal thinning of continental lithosphère «eaten» by warmer asthenosphere. But the process probably exceeds the imparted geological time. Better achievement is obtained by the model of Mlle Fleitout where the heating of the cold continental lower lithosphere proceeds from its replacing by advection of infra-oceanic matter.