Schematic model for the evolution of the Sheba ridge between Alula-Fartak and Socotra transform faults from OCT formation, onset of spreading to anomaly A5. The location of the inherited Mesozoic basins is indicated. At the OCT emplacement time (average 20 Ma), the OCT area is made of three segments separated by two accommodation zones. The formation of the OCT appears to be non linear and at 17.6 Ma (A5d) the onset of spreading occurs on the centre of the three segments, whose the western one propagates eastwards. At anomaly A5c (16 Ma), the ridge is made of an eastward-propagating segment and two others. At the anomaly A5 (10 Ma), the ridge consists of two segments between Alula-Fartak and Socotra transform faults with the eastern one splitting into two segments. See text for explanations.