Considering the jumps of rift zones over Iceland, and seeing the pace of those ‘jumps’, there seems to be a possibility that another rift zone opened before the ‘first one’.
The activity would then have occurred about 25 million years ago, probably at the same time as when the Northwest Rift Axis was active. The prospective rift axis is pointed out with a question mark.
The relevant scientific papers reveal the story and location of extinct rift zones and ridges, as shown here above.
Magic Magma 