The up-welling large concection rollls of lower mantle flow towards east and west under Iceland. The division line can be pinpointed. It is not directly under the Reykjanes Ridge, because the upper-most convection cells directly above the line have convergent flow. Therefore, the next division line is up-welling, criating the Reykjanes Ridge. Still, the main convection rolls of lower mantle have a ruling effect on tectonic drift, and many interesting places are found along it, or very close to it, including my hometown, Thorlakshofn.
From Thorlakshöfn, the montain slope called Hlíð marks the line. Then Hveragerði forms a major hub from the effects of different layers of the mantle, manifested by geothermal area. Then the slope of the western margin of the West Volcanic Zone includes Laugarvatn, anogher geothermal area. Geysir is found slightly east of the line, but still on the line of Hekla and Reykholtsdalur. Then we go farther along the edge of Langjökull Glacier, where the mountain range of Jarlhettur forms the division line on the surface. Then we encounter Hveravellir, an area that is dirctly in between the outposts of Icelandic volcanoes, Snæfellsjökull and Snæfell. Finally, in the northern part of Icealnd the line passes slightly east of Akureyri, the capital of the North. Not far from there, Húsavík, with hot spring areas and faults, marks the last landmark for the division line through Iceland.