The two plates of N-America and Eurasia are divided in four ways at the NE-corner of Iceland. The Tjörnes Fracture Zone is by no means simple, but it has been studied quite thoroughly.
The triple fault system follows closely convection rolls found at around 400 km depth:
Basic map from the article Plate boundaries, rifts and transforms in Iceland by Páll Einarsson in Jökull 2008.
The resemblance is striking, but here we tend to forget the volcanic component. The general idea can be derived from this map from Wikipedia, where the most relevant convection roll has been pointed out by thickening the outlines of upwelling and downwelling:
A detailed analysis according to tectonic studies, where the effect of different convection rolls layer is taken into account, would make us understand more clearly how the faults are aligned according to the polygons and division lines.
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:
Map base from Icelandic Institute of Natural History
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.
The outposts of Icelandic volcanoes are arranged regularly.
The outposts of Icelandic volcanoes
Snæfellsjökull and Snæfell have the same distance from a central point. The peaks of the mountains are also on exactly the same latitude. On the NS-axis of the central point, the craters on the top of both Hekla and Eyjafjallajökull are found. North of there, Drangey island is also a volcanic formation of the old Skagafjörður Rift Zone. On the same NS-axis, there is a point of the center of the Icelandic platform. Another NS-axis can be traced through Öræfajökull. Öræfajökull is the highest volcano, marking the southern end of a volcanic belt, very similar to the Snæfellsnes Volcanic Belt, and the ends of the two volcanic belts are Snæfellsjökull and Snæfell. Thereby, the outposts of Icelandic volcanoes can be said to be knitted to each other.
The grid of convection rolls explains the tectonic framework of Iceland:
Outlines of the Tectonic Framework of Iceland
The same applies for main volcanic and geothermal sites:
Some Volcanic and Geothermal Sites in Iceland
The tectonic framework shows direct resemblance with the model of convection rolls found under the country. Likewise, many volcanic and geothermal sites are found in context with the crossings of division lines of different layers of mantle convection rolls.
Besides this, we can look into the polygons of the network of division lines between convection rolls of different layers:
Polygons compared to distinct areas
The calderas along the central parts of Iceland have the function of providing magma for dikes to fill up the void created by tectonic drift.
It is obvious that the drift vectors only approach the alignment of the convection rolls in Iceland. The uppermost rolls are aligned from NE to SW, and in the NW part of Iceland these rolls should be driving the drift. Rolls opposing the drift should be decoupled, and rolls following the drift should be coupled.
Different layers can get coupled and decoupled, so the combined effect of lower layer can be felt at the surface with movements of the tectonic plate. An intersection layer is found between convection rolls layers, and between the upper most convection layer and the ductile lower most part of the tectonic plate as well.
With these factors in mind, it will be possible to analyse and trace the geological history.
To further show the double nature of the two rift zones of the southern half of Iceland, this map should be added:
The effect of the West Volcanic Zone added
The eastern margins of West Iceland Volcanic Zone and East Iceland Volcanic Zone are 3° apart from east to west along each parallel. The pulling effect of the North Americal Plate to the NW causes rifting, as the local small convection rolls underneath flow into opposite direction. This creates and area with rather northerly oriented drift vectors.
At Vatnajökull, the Eurasian plate slides along the side of the East Volcanic Zone, contributing to the fact that the geology of East Iceland has much more holistic appearence than that of West Iceland.
Magic Magma 