Relationship Of Supercontinents Lower Mantle Convection And The Geoid

Some models for the formation and dispersal of supercontinents suggest a link between mantle convection, heat flow, and the supercontinent cycle. Stationary supercontinents insulate the mantle, causing it to heat up, because the cooling effects of subduction and seafloor spreading are absent. As the mantle then heats up, convective upwelling is initiated, causing dynamic and isostatic uplift of the continent, injection of melts into the continental crust, and extensive crustal melting. These crustal melts are widespread in the interiors of some reconstructed supercontinents, such as the Proterozoic anorogenic granites in interior North America, which were situated in the center of the supercontinent of Rodinia when they formed between 1 billion and 800 million years ago.

After intrusion of the anorogenic magmas, the lithosphere is weakened and can be more easily driven apart by divergent flow in the asthenosphere. Thermal effects in the lower mantle lag behind surface motions. So, the present Atlantic geoid high and associated hot spots represent a "memory" of heating beneath Pangaea. Likewise, the circum Pangaea subduction zones may have memory in a global ring of geoid lows.

other models for relationships between supercontinents and mantle convection suggest that super-

The geoid is an imaginary surface that would be sea level if it extended through the continents. The geoid surface is perpendicular to the gravity plumb lines at every location.

continents result from mantle convection patterns. Continental fragments may be swept toward con-vective downwellings, where they reaggregate as supercontinents.

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