The Wilson cycle is an expansion to Wegener's theory of continental drift
theorized that all the continents as they are today were once joined in single large landmass, Pangea
. The Wilson cycle, named after J. Tuzo Wilson
who first proposed it, takes this a step farther--not only were the present continents once joined, but the process has occured multiple times throughout the geologic history of the Earth. There may have been as many as 6-10 occurences of this cycle since the early Proterozoic
period (see Rodinia
The Wilson cycle describes ocean basins, and the stages that they go through from creation to elimination. There are six seperate stages of the Wilson cycle:
Embryonic: Thick continental crust blocks the flow of heat, and there is a change in convection currents of the asthenosphere (the soft plastic layer on which the continental and ocean plates 'float'). There is an upwelling of magma, which causes continental rifting to begin. The East African rift valley system is an example of this process.
Youth: The rift expands as magma continues to rise to the surface and creates new crust, and water fills the young ocean basin, creating a 'linear ocean' like the modern Red Sea.
Adolescence: Our new ocean grows wider begins to age. The passive boundaries between the continent and the oceans are accumulating sediment from the erosion of the continents. The Atlantic Ocean is one such maturing ocean basin.
Maturity: The weight of accumulating sediments at the margin where continental crust meets the ocean basin causes depression of the ocean crust. Eventually, a subduction zone is formed, where the thinner, dense ocean crust slips below the continental crust. See Pacific Ocean as an example of this stage in ocean development.
Old Age: Accretionary wedges are formed as sediments are scraped off the subducting ocean crust which creates a tectonic crest which can form offshore island arcs. The ocean basin continues to narrow. This terminal stage of development is exemplified by the Mediterranean Sea.
Death: All of the oceanic crust that seperated the two masses of continental crust has been subducted, and the continents collide. This collision causes a mountain range to form along the collision- a suture. Examples of this type of landform are abundant, and include the Indus-Yarlung Zangbo suture in the Himalayas where India collided with Asia, and the Ural mountains which mark the collision of the Asian landmass with Europe.
This theory is an attempt to explain the presence of ancient orogenic belts, or zones that have undergone techtonic compression. The Appalachian Mountains are one of these orogenic belts that are evidence of the Wilson cycle- a collisional mountain range whose age dates to before the theorized breakup of Pangea, therefore there must have been seperate continents to collide before the supercontinent's existence.