Plume hypothesis challenged

Abstract

The hundreds of Earth scientists who challenge the existence of plumes of hot rock rising from Earth’s core–mantle boundary are not “a small but vocal subset” (Nature 504, 206–207; 2013). Rather than simply promoting the conventional wisdom, you should be encouraging the development of multiple working hypotheses. Many scientists have valid concerns that the originally postulated behavioural, geometric, chemical and thermal characteristics of mantle plumes have been widely discredited (W. J. Morgan and J. P. Morgan in Plates, Plumes, and Planetary Processes 65–78; Geological Society of America, 2007). The plume model has survived only by diversifying its supposed characteristics, which include a variety of compositions and feats such as tunnelling thousands of kilometres horizontally to emerge anywhere at any time, splitting, merging and pulsing (E. R. Lundin in 52 Things You Should Know About Geology 66–67; Agile Libre, 2013). There are no chemical or isotopic data that require deep- plume origins or anomalously high temperatures, and no reliable seismic-tomography results have ever revealed a plume. Plumes cannot account for the eruption rates of the largest flood basalts, which can best be explained by rapidly draining reservoirs of molten rock that have accumulated over long periods. There has been significant progress in developing an alternative model for anomalous volcanism (see, for example, G. R. Foulger Plates vs Plumes: A Geological Controversy, Wiley-Blackwell; 2010). This is better explained as a passive response to the stretching of lithospheric plates — for example, at rift valleys — which permits melt to rise from shallow depths in the mantle.