A naive Bayesian method to chase mantle plumes in global tomography models

Abstract

SUMMARY This study provides a quantitative approach to search for mantle plumes in global seismic tomography models without any preconceived notions about the associated mantle velocity anomalies, other than the assumption that the plumes are not significantly deflected horizontally by more than 6°, anywhere in the mantle. We design identification tests with a reasonable detection threshold while keeping false alarms at a level lower than 5 per cent. This is based on a naive Bayesian clustering analysis, which is possible thanks to the varimax principal component analysis that provides components of the tomography models that are much more independent than the original number of depth slices in the models. We find that using such independent components greatly reduces detection errors compared to using an arbitrary number of depth slices due to correlations between the different slices. We detect a wide range of behaviour of the seismic velocity profiles underneath the hotspots investigated in this study. Moreover, we retrieve locations away from hotspots that have similar seismic velocity profile signatures to those underneath some hotspots. Hence, it is not possible to obtain a unique definition of seismic velocity anomalies that are associated with hotspots and thus care needs to be taken when searching for mantle plumes beneath hotspots using prior assumptions about the velocity anomalies that might be associated with them. On the other hand, we establish a probability distribution of the seismic velocity profiles that is specific to a sublist of hotspots. Overall, the mantle plume zones identified in our analysis do not appear to surround the Africa and Pacific large low shear velocity provinces (LLSVPs), but are rather within them. This rules out the idea that LLSVPs correspond to compact, dense piles with mantle plumes rising from their edges. Instead, our analysis suggests two possible options that either the LLSVPs: (1) correspond to bundles of thermochemical mantle plumes or (2) are made up of compact piles topped by a bundle of plumes.