Absolute motion and evolution of the Bouvet triple junction

Abstract

The absolute motion of the Bouvet triple junction has an important role in its mechanical evolution. At present, the relative velocity vectors of the South American, African and Antarctic plates form an obtuse isosceles triangle, and both the ridge–ridge–ridge (RRR) and ridge–transform–transform (RFF) configurations of the Bouvet are potentially stable. Sclater¹ demonstrated that the Bouvet twice alternated between RRR and RFF in the past 20 Myr. The reasons for these changes are unclear, but the analysis of the absolute velocities of the two configurations presented here provides some insight; The motion of the RRR configuration of the Bouvet, with respect to a hotspot reference frame, carries the junction to the north-west (343°) at 14.7 km Myr⁻¹, whereas the RFF form moves to the south-east (157°) at only 5.8 km Myr⁻¹. The RFF configuration is stable only when the relative velocity triangle is precisely isosceles. As the RFF junction migrates away from the isosceles line, it becomes increasingly unstable, until it is forced to switch to RRR. The RRR junction then drifts back to the isosceles line where it reverts to RFF.