The triple-junction structure of mantle plumes and continental rifting

Abstract

Numerical experiments show that the hot thermal plumes in a convecting mantle have a complex 3-dimensional stucture that is approximately axisymmetric near the top of the convecting layer, but followed down towards the base of the layer evolves into a branched structure formed by the bifurcation of a hot sheet. The uplift above a thermal plume is thus characterised by a dominant axisymmetric component, to which a small, irregular, but characteristically triple-armed, perturbation is added. An explanation for the characteristic triple-junction geometry of continental rifts has long been sought in terms of the mechanical properties of the lithosphere, but these experiments suggest that the rift may inherit its basic geometry from the underlying thermal plume.