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.