Abstract

The boundaries of the Laurentian craton conform to edges of two adjacent faces on a truncated icosahedral projection of Earth. The congruence of the geology and the icosahedral tessellation has tectonic significance. It apparently originated as a large-scale fracture pattern during the tectonically quiet early Mesoproterozoic, 100–200 m.y. after Paleoproterozoic consolidation of a parent supercontinent. Homogeneous stretching of the young supercontinent across a geoid high above an insulated and thermally expanded mantle may have induced the fractures. Neoproterozoic and Cambrian rift zones exploited the icosahedral fractures during breakout of Laurentia, and miogeoclines accumulated along the margins. The Grenville and Appalachian orogenies appear to have shortened the tessellation. Because of its high geometric symmetry, the rift tessellation may provide a reference frame for restoration of an early Mesoproterozoic supercontinent.

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