How the Tectonic Plates are Divided

In Iceland, rift zones mark the division between N-American and Eurasian tectonic plates.

The green arrows show how the local convecion rolls oppose the drift of the large tectonic plates:

The Reykjanes Ridge, Reykjanes Peninsula and the West Volcanic Zone are found above the same convection roll. The flow underneath is opposite to the large scale tectonic drift of the North American Plate, and therefore rifts appear due to the pulling effect. The same happens 3° farther to the east within the East Volcanic Zone. The East Volcanic Zone is partly a rift zone, that is north of 64°N, but south of the parallel the tectonic drift direction follows the Eurasian Tectonic Plate. Still, the East Volcanic Zone continues southwards, creating the special circumstances of Katla and Eyjafjallajökull. and then the Vestmannaeyjar Polygon, Apparantly, Vestmannaeyjar have something in common with Snæfellsnes, being alcalic. The North Volcanic Zone is based on the same principle, as The main upwelling division line bends northwards, opposing downwelling lines. North of Iceland, the Grímsey volcanic system is based on a convection roll opposing the drift of the Eurasian Plate. It is not the only example, because the Öræfajökull Volcanic Belt is also based on such vectors, having upwelling lines at its eastern side, and downwelling ones at the western side.