Convection current theory by Arthur Holmes | Continental Drift support evidence | Geography Lectures

Описание: Arthur Holmes postulated convection current theory in the year 1928–29. It is widely accepted driving mechanism for Continental drift(moving apart) which lead to the foundation of modern plate tectonics.

His main objective was to find the scientific explanation of origin of the Continent and oceans. But it is also widely accepted concept of mountain building.

To understand Holmes theory, first of all you should have an idea of convection current. Convection Current is defined as “a process of continuous heating up of liquids or gases by the process called as Convection.
the convective currents are divided into two groups on the basis of their locational aspect e.g.:

(i) Convective currents of rising columns, and

(ii) Convective currents of falling columns.

The rising convective cur­rents after reaching the lower limit of the crust diverge in opposite directions.

This outward or divergent move­ment introduces tensional force due to which the crust is stretched, thinned and ultimately broken and the broken crustal blocks are moved apart. The wide open area between two drifting crustal blocks in opposite directions is filled with water and thus an ocean is formed. According to Holmes the equatorial crust was stretched and ruptured due to divergence of rising convective currents which carried the ruptured crustal blocks towards the north and south and Tethys Sea was formed.

This phase is called ‘opening of Tethys’ Again two sets of convergent or downward moving (descend­ing) currents brought Laurasia and Godwnaland to­gether and thus Tethys was compressed and folded into Alpine mountains. This phase is called ‘closing of Tethys’.

‘The convective mechanism is not a steady process but a periodic one, which waxes and wanes and then begins again with a different arrangement of centre’. It means that the convec­tive currents originate at several centres which are not permanent. Geosynclines are formed due to subsid­ence of crustal blocks mainly continental shelves due to compressive force generated by convergent convec­tive currents moving laterally together under continen­tal and oceanic crusts.

In other words, when the conti­nental and oceanic crusts move together and converge under the continental shelves, they descend downward and thus cause immense compression due to which the crust is subjected to subsidence to form geosyncline. The convective currents of rising columns under con­tinental and oceanic crusts bring materials in the geosynclines which are always located above the de­scending convective currents of falling column.

Con­tinuous compression and sedimentation causes gradual subsidence of geosynclines. Holmes has described a cyclic pattern of thermal convective currents which includes the origin of convective currents, formation of geosynclines, sedimentation and orogenesis and further rise in the mountains
Convection current theory
continental drift theory
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