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Iceland has been cited as the location of a hot-spot overlying a mantle plume (similar to that of the Hawaii chain in the Pacific), though for some time this model has been challenged (see Gillian Foulger's mantle plumes site, especially Lundin & Doré's article).

How does the recent announcement by Torsvik et al. (2015) — that south east Iceland is underlain by continental crust — affect this debate?

Reference

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    $\begingroup$ I haven't read the entire paper, but there's a red flag in the first sentence of the abstract: "The magmatic activity (0–16 Ma) in Iceland is linked to a deep mantle plume...". So no bias there :) $\endgroup$ – kwinkunks Apr 14 '15 at 14:58
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Yes, Iceland is an example of a hotspot overlying a plume. The plume has been imaged seismically, e.g., see the Science paper (Figure 3) by Montelli et al. (2004). It is available at http://www.sciencemag.org/content/303/5656/338

The 2015 paper you referred doesn't dispute that claim. All is says is that "The plume split off a sliver of continent from Greenland in the Early Eocene. This sliver is now located beneath southeast Iceland where it locally contaminates some of the plume-derived magmas".

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    $\begingroup$ Whether mantle plumes exist is still hotly debated. Proponents of the concept see results such as Montelli et al. as definitive proof. Opponents of the concept argue that Montelli et al. and others were seeing what they wanted to see. Tomographic mapping requires a background model. Assume a background model that involves mantle plumes, and voila! you see mantle plumes. Assume a background model that rejects mantle plumes, and voila! you don't see mantle plumes. $\endgroup$ – David Hammen Apr 14 '15 at 12:26
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    $\begingroup$ @DavidHammen There is also evidence from geochemistry. You should read the relatively recent paper by Kerr which is available at sciencemag.org/content/340/6128/22.full $\endgroup$ – stali Apr 14 '15 at 14:18
  • $\begingroup$ Montelli's research (e.g. as described in this PDF; look at figure 3) suggests that Iceland's hotspot is not caused by a plume, assuming 'plume' has its usual meaning: a deep-seated upwelling connected to the core-mantle boundary. $\endgroup$ – kwinkunks Apr 14 '15 at 14:52
  • $\begingroup$ A plume starts deep but doesn't have to be deep seated forever. When it ceases the deep part will be the first to disappear and therefore you might only see its remnants at the very top. Also, the deeper parts of the plume are much narrower and harder to image to begin with. Look at the images in the link mentioned in my answer (both P and S wave results). $\endgroup$ – stali Apr 14 '15 at 18:03
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    $\begingroup$ @stali: Montelli's words: "The results of our inversion [...] clearly contradict [...] a plume extending all the way to the core-mantle boundary" (i.e. what most people call a plume). So your evidence doesn't really support the bold first sentence of your answer, which is just one side of a contested claim, perhaps even the minority side. I think you should at least recognize the debate in your answer. PS, if poss, please avoid referencing pay-walled material. $\endgroup$ – kwinkunks Apr 14 '15 at 22:16

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