A detailed 3-D tomographic model of the whole mantle beneath the
circum-Arctic region is obtained by applying an updated global
tomography method to a large amount of P-wave arrival time data.
Our model clearly shows the subducted Izanagi and Farallon slabs
penetrating into the lower mantle beneath Eurasia and North America,
respectively. In the region from Canada to Greenland, a giant stagnant
slab lying below the 660-km discontinuity is revealed. Because this slab
has a texture that seems to be due to subducted oceanic ridges, the slab
might be composed of the Izanagi, Farallon, Kula and Vancouver slabs
that had subducted during ~80−20 Ma. During that period,
a complex rift system represented by division between Canada and
Greenland was developed. The oceanic ridge subduction and hot upwelling
in the big mantle wedge above the stagnant slab caused a tensional
stress field, which might have induced these complex tectonic events.