Note
    In the original thesis version, multiplication of finite plate rotations for the purpose of computing hotspot tracks had been carried out in the wrong order. This affects some of the figures and tables, however, to my best knowledge, all results and conclusions remain qualitatively valid. This error had been corrected prior to any subsequent publications. In the version made available here, Figures 1, 20 and 23 are replaced by corrected ones, but some more figures and tables are also affected and have not yet been corrected.