A main outcome of our study is that this passive margin is not continuously of the volcanic type and that the change from a non-volcanic to a volcanic margin occurs abruptly.
We define four distinct First-order Segments along the 2400聽km section of the southwestern African margin covered by our seismic data. From south to north these First-order Segments are: Magma-poor Segment I; Segment II with enormous SDRs volumes; decreasing SDRs volumes in Segment III; Segment IV again with enormous volcanic output, likely influenced by Walvis Ridge volcanism.
Most important is that there is no systematic increase in the volumes of the effusives towards the Tristan da Cunha hot-spot. Rather there is an alternating pattern in the SDRs' volumes and widths.
The boundary between the volcanic and magma-poor margin segments in the southernmost study area is sharp (10s of km), which we propose is reflected in magnetic anomaly data as well. We suggest that this variability along the margin is mainly due to a change in stretching/rifting character from oblique during the early stages of breakup to conventional seafloor spreading from Chron M4 (鈭?30聽Ma) onwards.