Juan de Fuca follows a convection rolls division line.
This arrangement is comparable to the Reykjanes Ridge and the volcanic zones in Iceland.
The ridge does originally not follow the main division line, because it is down-welling and therefor convergent.
The position of the two ridges can be compared:
Note that the main ridges are mainly found 1.5° west of the division line between large convection rolls of lower mantle.
Same kind of shift from western side to eastern side, a jump of 3°, is found in both cases. From the Reykjanes Ridge, a jump occurs to the East Volcanic Zone of Iceland, but at Juan de Fuca, a jump of 3° is found for the Gorda Ridge.
The fact that Juan de Fuca and Reykjanes Ridge show two aspects of consistency, that is they both follow the same formula of alignment, and are found 1.5° west of main division lined of lower mantle, is an argument for siting that the model is in harmony with real circumstances within the Earth’s mantle.
The concection rolls system within the Earth is regularly shaped, carrying heat to the surface. Two layers within the depth of 120-410 km are responsible for many tectonic and topographic features. The volcanic zones of Iceland can be traced accordingly. The first step is to see how the upper most rolls shape two of the main volcanic zones in Iceland, the West Volcanic Zone and the East Volcanic Zone.
Here, the upper most rolls are drawn with thicker lines for clarity.
Blue lines show down-welling, and there the volcanic zones terminate sharply at the eastern side. The East Volcanic Zone is the best example, because the rifting takes place exactly within the area marked by up-welling and down-welling lines.
The Reykjanes Ridge itself also provides a very easily understood example of how this system works. Therefore, the two rolls are drawn there.
As this is nature, not man made system, it is represented in countless ways throughout the country. The earthquake epicenters also show some functional aspects of the grid of division lines of different layers.
It also has to be kept in mind that under Iceland between 120-410 km depth, there are actually four layers, due to the intersection between the two layers north of the country, and the other two layers south of it.
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:
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:
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.
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:
The same applies for main volcanic and geothermal sites:
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:
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.