I may be wrong, but there is only one plume system to my immediate knowledge, and that’s Hawaii. Thus I’d find it odd for one to be so far in from the western continental margins, which have definitely demonstrated active tectonic activity over the past several hundred million years.
Rather, it’s plausible that some or most of Yellowstone’s heat sources are remnants of these earlier - and ongoing - subduction systems...but I’d have to review the geology and geophysics of the region to be more sure.
Iceland is a combo plume + sits atop a spreading center.
Iceland is above a plume + sits atop a spreading center. The spreading center supposedly drifted over the plume.
Another geophysical anomaly is the earthquake zone around Missouri/Illinois/Kentucky where the monstrous series of earthquakes happened in 1811-12 known as New Madrid. This area is nowhere near a coast either. Of course the Tethys Sea once covered that area, but how many million years ago was that?