For those that do not know, Iceland is actually an exposed section of oceanic crust on the Atlantic Ridge. The volcanism is from the sea floor being torn apart along the ridge.
additionally, iirc it is on top of a mantle plume. Iirc this plume is believed to have formed at the then-location of the siberian traps - if correct, this plume was directed caused (antipodally) by the P-T impact.