RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES3001, doi:10.2205/2005ES000179, 2005
[73] Two-dimensional numerical modeling of thermal convection in a mantle with two floating continents has shown that movements of the continents obey certain laws. Continents are coupled with the mantle through thermal and mechanical interactions, so that not only does the mantle affect continents, but the continents themselves reorganize mantle flows.
[74] An inevitable stage of the drift of continents, which are pulled into areas of cold descending convective flows, is their convergence and the formation of a supercontinent. The supercontinent gives rise to the heat-screening effect, causing the heating and decompaction of the underlying cold matter of the mantle. As a result, the descending flow beneath the supercontinent gives way to a giant ascending mantle flow withdrawing heat from the mantle base. Floating-up diapirs and thermals arise periodically at the center of the broad ascending flow beneath the supercontinent. The effect of the ascending flow eventually leads to the breakup of the supercontinent. As parts of the supercontinent diverge, the hot mantle flow is intensified and its heat outflux increases to about 200 mW m-2. However, the heat flux above the diverging continents remains on the order of 20-30 mW m-2. After a certain time, a structure of the Atlantic Ocean type arises between the continents; this structure includes a mid-ocean ridge characterized by high values of the heat flux. The cold mantle region (corresponding to the oceanic lithosphere) thickens away from the ridge axis. Outside this region, a structure of the Pacific Ocean type arises, including subduction zones where the oceanic lithosphere plunges into the mantle under continents.
[75] Numerical experiments have shown that the continental lithosphere changes with time in thickness and shape. The continental lithosphere thickens when a continent is located above a colder mantle region and thins when it is above a hot mantle region. Since the temperature in the mantle varies significantly along a continent, the shape of the continental lithosphere should also vary. Its thickness decreases in regions where a hot plume approaches the lithosphere, and deep roots grow at continents in regions of an anomalously cold mantle. As regards the oceanic parts of lithospheric plates, they can be compared to ice floes temporarily freezing to continental edges.
[76] The continental lithosphere can be tentatively subdivided into two parts: the older and lighter metamorphized upper part and the younger lower part differing from the underlying mantle only by a higher viscosity. The older upper part of the continental lithosphere is more stable, whereas the lower part permanently varies. In softened higher-temperature regions material of the continental lithosphere is washed away by mantle flows. This accounts for great differences in continental lithosphere both between different continents and within each continent.
Citation: 2005), Evolution of mantle plumes and uplift of continents during the Pangea breakup, Russ. J. Earth Sci., 7, ES3001, doi:10.2205/2005ES000179.
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