Hotspots, polar wander, Mesozoic convection and the geoid

Abstract

The geoid bears little relation to present tectonic features of the Earth other than trenches and hotspots. The Mesozoic supercontinent of Pangea, however, apparently occupied a central position in the Atlantic–African geoid high. This and the equatorial Pacific geoid high contain most of the world's hotspots^1,2. The plateaus and rises which are now in the western Pacific formed in the Pacific geoid high and this may have been the early Mesozoic–late Palaeozoic position of a large part of Asia and other fragments of the Pacific rim continents. The major global geoid highs were regions of extensive Cretaceous volcanism and may be the former sites of continental aggregations and mantle insulation and, therefore, hotter-than-normal mantle. The pent-up heat causes rifts and hotspots and results in uplift, magmatism, fragmentation and dispersal of the continents and the subsequent formation of plateaus, aseismic ridges and seamount chains which cause a global rise in sea-level. Convection in the upper mantle caused by such lateral temperature gradients is intrinsically episodic. A geoid anomaly of 50 m can be formed in about 100 Myr by continental insulation. We show here that such geoid anomalies are long-lived and may be used to remove the ambiguity in early Mesozoic–late Palaeozoic plate reconstructions. Geoid highs control the rotation axis of the Earth and, in effect, bring long-lived continental aggregations to the Equator. Many aspects of continental geology such as vertical-tectonics and episodicity of magmatism and transgressions can be explained by continental insulation.