TRUNCATED ICOSAHEDRAL BREAKUP OF SUPERCONTINENTS

On at least two occasions in earth history, the breakup of supercontinents was accompanied by anorogenic magmatic activity along rift zones that followed truncated icosahedral (TI) arrangements. A TI pattern is geometrically rigorous, consisting of a tessellation of regular hexagons and pentagons with edge lengths subtending 23.28 degrees of arc.

Pangaea broke apart along rift zones that followed 20 edges of a TI tessellation, and large igneous provinces and dike swarms erupted near TI edges during outbreak of hotspots. We show by robust parametric and non-parametric tests that a group of 35 hotspots that first became active during Mesozoic breakup of Pangaea are statistically distributed along TI edges between Iceland and Kerguelen. These active hotspots are enclosed within the modern Atlantic-African positive geoid anomaly on the Mesozoic site of Pangaea, and the TI defined by the hotspots is symmetrical with respect to the anomaly. In an older example, early Mesoproterozoic Laurentia broke out of its parent supercontinent accompanied by anorogenic magmatic provinces, dike swarms and continental rift zones that coincide with parts of eight sides of a TI tessellation.

In both examples, the TI rift episodes and magmatic outbreaks followed hypothetical development of a geoid high after a cycle of supercontinent consolidation and stagnation. The TI pattern provides the minimum total edge length for hexagonal fragmentation of a sphere, and is therefore a minimum energy configuration. Uniform layer-parallel extension of a large spherical shell may favor a TI fracture pattern. Such a condition may result from evolution of a large positive geoid anomaly beneath a stalled supercontinent.