When we say that Iceland belongs to two tectonic plates which drift away from each other, we also say that two different mantle currents exist under the country. Well… we usually skip the latter part 🙂 Still it is what we mean by drifting – a current takes the huge plates and moves them! As I have analyzed these currents, we can compare that analysis with the division line between the continents according to drift vectors measured with GPS technology.
The black line is the division line of the main convection lines of lower mantle. The red line shows the main division line in between the two tectonic plates of N-America and Eurasia. The thin lines show the network of smaller convection roll layers.
To fully comprehend this, one has to read the book first 🙂 But the base is simple – regular convection current rolls with the same height and width – just physics.