Beyond hotspots – the importance of rift history for volcanic margin formation.

Largely on the basis of detailed observations from the North Atlantic Ocean, mantle temperature has been identified as the primary factor controlling magmatic production during rifting, with observed variations in volcanic activity at rifted margins explained in terms of the mantle temperature at the time of break-up. However, as more detailed observations have been made at other rifted margins worldwide, the validity of this interpretation and the importance of other factors in controlling the style of break-up have been much debated. One such observation is from the northwest Indian Ocean, where, despite an unequivocal link between an onshore flood basalt province, continental break-up and a hot-spot track leading to an active ocean island volcano, the associated continental margins show little magmatism. Not all rift succeeds in break-up and sea-floor spreading and it is this rift history that is key. I will show that the volume of rift-related magmatism generated, both in the northwest Indian Ocean and at the better-known North Atlantic margins, depends not only on the mantle temperature but, to a similar degree, on rift history. The inherited extensional history causes break-up to go with a bang or a whimper.