The Emperor’s HeadOur modern thinking behind hotspots is that they are generated by mantle plumes. A

The Emperor’s HeadOur modern thinking behind hotspots is that they are generated by mantle plumes. A huge plume of extra warm mantle rises up to the surface, triggering formation of a large igneous province – a huge pile of igneous rocks somewhere on the surface. That is followed by a long chain of volcanoes, produced by warm mantle continuing to rise up the pipe formed by the plume.The best established example of this sequence on Earth is the Hawaiian-Emperor seamount chain, a chain of volcanoes starting at Hawaii and extending all the way to the Kamchatka Peninsula, where the chain ends at a subduction zone. Thus, although Hawaii is an extremely well-developed chain of hotspot volcanoes, it is missing one thing – the plume head!Hawaii’s large igneous province isn’t there – either it was subducted, or something is very different about the Hawaiian chain and we don’t understand plume formation at all.A new paper purports to answer this question. Using seismic waves that head through the Earth and powerful supercomputers, scientists are able to detect pieces of material that went down subduction zones, and as data and computers improve they can find these pieces even if they’re now deep inside the planet.800 kilometers deep beneath the Kamchatka Peninsula, there is a 1000-kilometer wide piece of crust that appears extra thick – a group of authors from several US universities and led by a scientist from Michigan State just proposed that this section of thickened crust represents the Hawaiian plume head. It would have been subducted between 20-30 million years ago, to reach the current depth.While this hypothesis is interesting, it is difficult to test. We’ll never drill down that deep to actually sample this stuff, and the thickened crust could also be related to interaction between the subducted plate and boundaries in the mantle. To confirm this hypothesis, scientists will somehow need to either find pieces of this plateau that stuck to Kamchatka and can be firmly tied to its formation, or come up with a full model for plate motion that includes this plateau.Interestingly, the bend in the Hawaiian-Emperor chain would have happened before this proposed plateau was subducted, so somehow the hypothesis requires that it hit Kamchatka and went down fairly easily, which is the opposite behavior of many other subducted oceanic plateaus. For example, the massive Ontong-Java plateau hit a subduction zone in the Southwestern Pacific and was so large that it shut down the subduction zone entirely, causing a new set of faults to form on the opposite side of Papua New Guinea, so somehow this plateau went down far easier.-JBBOriginal paper:https://science.sciencemag.org/content/370/6519/983 -- source link

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