TESSELLATED HOTSPOTS IN THE FOOTPRINT OF PANGAEA: RAYLEIGH-TAYLOR MANTLE DIAPIRISM TRIGGERS SUPERCONTINENT BREAKUP AT PALEOZOIC-MESOZOIC TRANSITION

Hotspots associated with the fragmentation of Pangaea, from Iceland to Kerguelen, lie on the spokes and hubs of an icosahedral tessellation that defines the planetary maximum for polygonal cells at the Earth's surface. Anderson (1982) showed that Pangaea and its hotspots occupy the locus of the Atlantic-African geoid high when the supercontinent is restored according to Morgan's (1981) hotspot model. The hotspot tessellation has two planes of symmetry that coincide with two planes of symmetry for the geoid high. Anderson (1982) concluded that insulation from slow-moving Pangaea led to intrinsically episodic convection in the upper mantle, elevation of the geoid anomaly, and outbreak of hotspots. The hotspot tessellation may herald Rayleigh-Taylor (RT) convection in the upper mantle, in which low density, low viscosity partial melt flows outward from the centers of cells to a polygonal matrix of spokes, and along spoke ridges to hub diapirs. The minimal dispersion of the hotspots from an ideal icosahedral tessellation supports an upper mantle influence for hotspot plumbing, consistent with lateral heterogeneities of the phase velocity c of 75 s-period Rayleigh waves (cf. Nataf, 2000). Due to mantle heterogeneities, diapirs episodically erupted from the hubs during the fragmentation of Pangaea, in some cases producing flood basalts. In some cases, dike swarms and rift zones followed tessellation spokes and broke out new continental margins. The proposed RT diapirism pattern supports models in which mantle insulation induced breakup of Pangaea at the Pz-Mz transition.