The non-parallelism of linear chains of islands and seamounts associated with hot spots indicates that the hot spots are not always stationary and so, while the chains can be interpreted in terms of plate tectonics, they are not prime evidence for plate tectonics as was originally thought.

Rollback -- the hinge line of the subducting plate recedes faster then the overriding plate moves forward then the over riding plate must extend to fill the gap (Hancock, 1994).

The subducting plate is to beneath a retreating plate. Then a back arc opens where the retreating plate has been most weakened by heat.

Back-arc basins of the world

Relative plate velocities: The blue arrows show the rate and direction at which plates diverge. The length of an arrow represents the velocity. Absolute plate velocities: The red arrows show the velocity of the plates with respect to a fixed point in the mantle.