Origin and evolution of the Kolbeinsey Ridge and Iceland Plateau, N-Atlantic

Variations in crustal structure along the 700 km long KRISE7 refraction/reflection and gravity profile, straddling 66.5 degrees N across the Iceland Shelf, Iceland Plateau and western Norway Basin confirm that extinct spreading centers coexisted with the now extinct aegir Ridge prior to the initiation of the Kolbeinsey Ridge at 26 Ma. The western 300 km of the profile, across the Iceland shelf, formed by rifting at the Kolbeinsey Ridge, whereas the eastern 400 km, across the Iceland Plateau and the western Norway Basin, formed by earlier rifting, possibly containing slivers of older oceanic or continental crust rifted off the central E-Greenland margin along with the Jan Mayen Ridge. Crustal thickness increases gradually across the Iceland shelf, from 12 to 13 km near the Kolbeinsey Ridge to 24-28 km near the eastern shelf edge, decreasing abruptly across the shelf edge, to 12-13 km. The Iceland Plateau has crustal thickness ranging from 12 to 15 km decreasing to 5-8 km across the western Norway Basin and 4-5 km at the aegir Ridge. We suggest that high-velocity lower crustal domes and corresponding gravity highs across the Iceland plateau mark the location of extinct rift axes that coexisted with the aegir Ridge. Similar lower crustal domes are associated with the currently active rift segments within Iceland and the Kolbeinsey Ridge.