Plumes and the splitting of continents

It has been noted for many years that the emplacement of continental flood basalts is closely associated in time with continental break-up. Consequently, there is general agreement that the two events are linked, but there is a lack of consensus as to which event came first in space and time. Was it the rifting of a supercontinent? Or did the emplacement of the flood basalt give rise to the break-up of a super-continent?

It will have been seen that there are three main types of model. These are:

(1) A plume arrives at the asthenosphere/lithosphere boundary beneath an already existing zone of lithospheric thinning, which, until the arrival of the plume, had not reached the critical degree of extension necessary to cause continental rifting.

(2) A plume-head which is sufficiently energetic to give rise to significant thinning of the lithosphere arrives at the base of continental plate, prior to the eruption of the magma produced by the plume.

(3) The emplacement of the LIP is sufficient to induce continental break-up with the subsequent development of an ocean.

It was first suggested that a major plume alone could give rise to lithospheric rifting, leading to a passive margin and the development of an ocean. However, this concept did not gain general support because of the theoretical difficulty in providing the amount of melt necessary to form a CFB. To overcome this shortcoming, it was argued that the required amount of melt could be produced if the plume entered lithosphere which was already experiencing extension. The proposed erosion mechanism is merely a way of producing lithospheric thinning without relying on previous lithospheric extension. Let us consider the relative merits of these models.

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