Plates, plumes and planetary processes / Плиты, плюмы и планетарные процессы

The turn of the twenty-first century ushered in an upsurge of questioning of then-current views of the links between mantle convection and surface kinematics and volcanism. Since the early 1970s the mantle plume hypothesis had been the most popular explanation for volcanism apparently not explained by plate tectonics, including both large-volume magmatism and volcanism in regions distant from plate boundaries.
In 1963 J. Tuzo Wilson attributed the Hawaiian and some parallel Pacific island chains to volcanism above rising currents of convection cells in the upper mantle. This hypothesis was developed and expanded by W. Jason Morgan in 1971, who proposed a mechanism for the formation and sustaining of “hotspots” as sources of anomalous surface volcanism. Morgan’s plume hypothesis envisaged a cylindrical column of hot material rising from the deep mantle to continually feed the surface volcanism. Furthermore, he proposed approximately twenty likely locations for such plumes, namely, Hawaii, Iceland, Yellowstone, the Azores, Easter Island, the Galápagos, Réunion, and about twelve others. Plume theory provided an elegant explanation for timeprogressive volcanic chains and relative fixity among melting anomalies on diverse plates. It also offered a reference frame for kinematics, appealing because in plate tectonics, no continent or boundary type can be assumed to be fixed. Morgan’s original plume hypothesis makes definite, testable predictions; starting with an observed hotspot track on one plate, and the known relative motion between two plates, predicted tracks on other plates are uniquely calculable.
Major later expansions of the hypothesis included the proposals that plume development involves a plume-head/plumetail sequence, represented by the emplacement of large igneous provinces followed by time-progressive volcanic chains, and that lower-mantle and core-mantle–boundary geochemical tracers may be identified in hotspot basalts. Many more plumes than the original twenty or so were proposed, popular lists typically containing fifty to one hundred candidates. Planetary scientists extended the hypothesis to other terrestrial planets, and applied it to explain features interpreted as volcanic on Venus and Mars. Nevertheless, many scientists are disappointed at what they consider to be the limited ability of the hypothesis to predict observations. Skeptics point out, for example, that the association of large igneous provinces with time-progressive volcanic chains is the exception rather than the rule, that many chains are not time progressive, that hotspots apparently are not relatively fixed, and that the interpretation of some geochemical species as being of deep-lower-mantle origin is not safe. They decry what they see as too little criticism of the plume explanation for volcanism and note instances of discrepancies being “explained” by samples not yet observed, or proposed local variations in the nature of the presumed plume. <....>