DO MANTLE PLUMES EXIST?

The “Plates vs. Plumes” controversy regarding whether deep mantle plumes exist or not is one of the foremost debates in current Earth Science. The Plume Hypothesis envisages a large, thermal diapir that rises from the core-mantle boundary and actively penetrates the lithosphere causing volcanism. It is powered by thermal energy from Earth’s core, works through convection in the mantle, and is independent of the lithosphere. Magmatism is actively driven and its quantity and chemistry reflect the temperature and composition of material in Earth’s deep mantle.

The Plate Hypothesis, its rival, is the conceptual inverse. It envisages simple leakage of magma to the surface from shallow depth as a passive reaction to lithospheric extension that opens pathways [http://www.mantleplumes.org/]. In this model, magmatism is powered by the forces that drive plate tectonics (likely primarily slab-pull), it is not driven by mantle convection, and it is unrelated to the deep mantle. Magmatism is passive and its quantity and chemistry reflect the fusibility and composition of local shallow source materials.

Many scientists feel that the greatest barrier to resolving the debate is not lack of scientific data but a philosophical problem. In that context it is instructive to consider the philosopher Imre Lakatos’ “methodology of scientific research programmes” in which the Plate and Plume hypotheses constitute competing research programmes. In Lakatos’s methodology, a research programme consists of a “hard core” – the central hypothesis – and a “protective belt” – a body of auxiliary hypotheses added to explain failed predictions. A research programme is “progressive” if the auxiliary hypotheses generate successful predictions and “degenerative” if they merely accommodate the data used in their formulation. The central questions in the “Plates vs. Plumes” debate are: (a) whether the Plume Hypothesis is “degenerative” and thus no longer worth pursuing; and (b) whether the Plate Hypothesis is likely to be a progressive research programme.

The history of competing research programmes in Earth Science can inform, and possibly help to resolve, the “Plates vs. Plumes” debate. We will describe the debate and compare it with past Earth Science debates to explore this new investigative avenue.