Superplumes or plume clusters?

It is proposed that the broad, seismically slow, mantle structures under Africa and the Pacific, often identified as superplumes, are instead spatial clusters of smaller plumes. Seismic data, including ScS-S differential travel time residuals and tomographic inversions using ScS-S and deep turning S data, show the breakup of so-called superplume regions into smaller structures. For example, the superplume under Africa is clearly formed by at least two and possibly three distinct plumes while the superplume under the Pacific consists of at least six smaller plumes. Enhanced seismic resolution may reveal even smaller-scale structures in the superplume regions. Dynamical considerations argue for the plausibility of superplume regions being clusters of smaller plumes whose heads might have merged into a large region of hot and buoyant material. Alternatively, the superplumes may simply be large, passively upwelling regions that are seismically distinct.