The Reykjanes Ridge is like a long mountain on the sea bottom. It is obviously being pulled to east and west, so convection rolls must be at its sides. The shape can be traced in a mathematical way, and drawn like that:
Everyone can trace this and compare with a map, for instance on Google Map, that the red line exactly shows the location of the top of the Reykjanes Ridge. The convection roll between the black line and the red pulls to the east, the other roll pulls to the west.
To make the drawing less confusing, let us omit lower rolls, showing clearly the small rolls shaping the Reykjanes Ridge:
Actually, the main division line of large mantle cells (black line) is not below the Reykjanes Ridge, because the small convection rolls under the tectonic plate at that location are convergent. The divergent convection rolls at the two sides create the Reykjanes Ridge, and then north of 64°N the EVZ appears.
In this way, the tectonics can be understood quickly by comparing to the convection rolls.
Still, in this way you do not have the whole story. Of course, there are more chapters that have to be learned to further analyzing the various complications of relationship between tectonics and mantle currents. This is a section of one chapter out of many 🙂
Magic Magma 