Читать книгу Earth Materials онлайн

49 страница из 155

Source: Courtesy of USGS.

Hotspotslinear seamount chains,

ssss1 (a) Linear seamount chain formed by plate movement over the Hawaiian hotspot and/or hot spot motion.

Source: Tarduno et al. (2009). © The American Association for the Advancement of Science;

(b) Mantle plume feeding surface volcanoes of Hawaiian Chain.

Source: From USGS.

Mantle plumessuperplumessupercontinent cycle

The picture has become considerably muddled in the twenty‐first century. Many Earth scientists have offered significant evidence that mantle plumes do not exist (Foulger et al. 2005). Others have suggested that mantle plumes exist, but are not fixed (Nataf 2000; Koppers et al. 2001; Tarduno et al. 2009). Still others (Nolet et al. 2006) suggest on the basis of fine‐scale thermal tomography that some of these plumes originate near the core–mantle boundary, others at the base of the transition zone (660 km) and others at around 1400 km in the mesosphere. They suggest that the rise of some plumes from the deep mantle is interrupted by the 660 km discontinuity, whereas other plumes seem to cross this discontinuity. This is reminiscent of the behavior of subducted slabs, some of which spread out above the 660 km discontinuity, whereas others penetrate it and apparently sink to the core–mantle boundary. Recent advances in new imaging methods that use powerful supercomputers have suggested that plumes originating near the base of the mantle do exist beneath many hotspots (French and Romanowicz 2015; Nelson and Grand 2018; Sanni et al. 2019) including Yellowstone, Hawaii, and Iceland, even though they are not always vertical. Wang et al. (2017) demonstrated that most groups of hotspots migrate very slowly, if at all, over time. It is very likely that hot spots are generated by a variety of processes related to mantle convection patterns, but these are still not well understood. Deep Earth tomography will continue to be an exciting area of Earth research over the coming decade.