2.6: The Wilson Cycle

The Wilson Cycle is named for J. Tuzo Wilson who first described it in 1966 [24], and it outlines the ongoing origin and breakup of supercontinents, such as Pangea and Rodinia [77]. Scientists have determined this cycle has been operating for at least three billion years and possibly earlier.

Figure \(\PageIndex{1}\): Diagram of the Wilson Cycle, showing rifting and collision phases. (By Hannes Grobe; CC BY-SA 2.5 via Wikimedia Commons.)

There are a number of hypotheses about how the Wilson Cycle works. One mechanism proposes that rifting happens because continental plates reflect the heat much better than oceanic plates [78]. When continents congregate together, they reflect more of the Earth's heat back into the mantle, generating more vigorous convection currents that then start the continental rifting process [79]. Some geologists believe mantle plumes are remnants of these periods of increased mantle temperature and convection upwelling and study them for clues about the origin of continental rifting.

The mechanism behind how supercontinents are created is still largely a mystery. There are three schools of thought about what continues to drive the continents further apart and eventually bring them together. The ridge-push hypothesis suggests after the initial rifting event, plates continue to be pushed apart by mid-ocean spreading centers and their underlying convection currents. Slab-pull proposes the plates are pulled apart by descending slabs in the subduction zones of the oceanic-continental margins [80]. A third idea, gravitational sliding, attributes the movement to gravitational forces pulling the lithospheric plates down from the elevated mid-ocean ridges and across the underlying asthenosphere [81]. Current evidence seems to support slab pull more than ridge push or gravitational sliding.

Figure \(\PageIndex{2}\): In this model, there are three forces working to move the plates. Ridge-push forces cause two plates to pull apart on the surface. Slab-pull forces pull the plates down. This movement of out-and-down is also encouraged by convection traction, or clockwise and counterclockwise currents that are present beneath the plates. (By Steven Earle; CC BY 4.0 via Physical Geology.)

References

• 24. Wilson, J. T. Did the Atlantic close and then re-open? (Nature, 1966).
• 77. Zhao, G., Cawood, P. A., Wilde, S. A. & Sun, M. Review of global 2.1–1.8 Ga orogens: implications for a pre-Rodinia supercontinent. Earth-Sci. Rev. 59, 125–162 (2002).
• 78. Pollack, H. N., Hurter, S. J. & Johnson, J. R. Heat flow from the Earth’s interior: Analysis of the global data set. Rev. Geophys. 31, 267–280 (1993).
• 79. Li, Z. X., Li, X. H., Kinny, P. D. & Wang, J. The breakup of Rodinia: did it start with a mantle plume beneath South China? Earth Planet. Sci. Lett. 173, 171–181 (1999).
• 80. Conrad, C. P. & Lithgow-Bertelloni, C. How mantle slabs drive plate tectonics. Science 298, 207–209 (2002).
• 81. Spence, W. Slab pull and the seismotectonics of subducting lithosphere. Rev. Geophys. 25, 55–69 (1987).