WHAT CAUSED THE CHANGE IN PACIFIC PLATE MOTION THAT PRODUCED THE MARIANA ARC?
If we bear in mind that plate motions are dominantly controlled by ‘slab pull’, then anything which reduces the slab-pull force will encourage changes in the direction and speed of plate motion. It is notable that in the southeastern Pacific the Aluk Ridge (spreading centre) began to progressively subduct along the Antarctic Peninsula; at the same time, the northwestern Pacific the Kula Ridge began to subduct beneath the Aleutians – Kamchatka. A result was a marked reduction in the N S slab-pull, because recently formed hot lithosphere is not very dense and not keen to subduct. In combination with other plate re-configuring events worldwide, this may have been enough to cause switch in Pacific Plate motion from N S to E W. But see Richards et al.
