Evolution of Triple Junctions

Abstract

THE boundaries between the rigid plates which make up the Earth's crust are recognized as being of three distinct kinds: ridges, from which new crustal material spreads symmetrically ; trenches, at which plates descend back into the mantle ; transform faults, along which plates may slip relative to each other^1–5. An important concept is the triple junction⁶, which is the point at which three plate boundaries meet. Discussions of the development of oceanic and continental crustal features almost inevitably contain considerations of motion, stability and instability of triple junctions. McKenzie and Morgan⁶ showed there are sixteen possible triple junctions and set out rules for examining their stability. They concluded that fourteen of them were stable under certain conditions. Here I point out that fifteen of the triple junctions are stable in the appropriate conditions.