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THE WILSON CYCLE AND SUPERCONTINENTS


Published on: 12/14/2020 5:49:34 AM

Geologic evidence has shown that ocean basins have opened and closed many times in the geologic past. The cycle of opening and closing is called the Wilson cycle, named for the Canadian geophysicist J. Tuzo Wilson.

The Wilson cycle begins with continental rupture and the formation of a wide ocean basin with passive margins. As the plates reverse their motion, and the ocean basin begins to close, oceanic lithosphere fractures and new subduction boundaries take shape. Island arcs soon appear and grow. Eventually, fractures occur at the continental margins, and the arcs collide with continents, producing arc-continent orogens. In the final stage, the orogens collide, producing a continental suture.

Geologic evolution of our Planet

As noted above, there is strong evidence that all the continents were once joined in a supercontinent, Rodinia, about 600 million years ago. Rodinia then broke apart, with its continents converging again about 400 million years later into the supercontinent Pangaea. There may have been as many as 6 to 10 such cycles of supercontinent formation, followed by breakup, in the Earth's ancient history. This time-cycle of supercontinents now is the basic theme of the geologic evolution of our planet.

Stage 1: Embryonic Ocean Basin

The Red Sea separating the Arabian Peninsula from Africa is an active example.

Stage 2: Young Ocean Basin

The Labrador Basin, a branch of the North Atlantic lying between Labrador and Greenland, is an example of this stage.

Stage 3: Old Ocean Basin

This includes all of the vast expanse of the North and South Atlantic oceans and the Antarctic Ocean. Passive margin sedimentary wedges have become wide and thick.

Stage 4A

The Ocean basin begins to close as continental plates move together. New subduction boundaries begin to emerge.

Stage 4B

Island arcs have risen and grown into great volcanic island chains. These are found surrounding the Pacific plate, with the Aleutian arc as an example.

Stage 5: Closing Continues

Formation of new subduction margins close to the continents is followed by arc continent collisions. The Japanese Islands represent this stage.

Stage 6

The ocean basin has finally closed with a collision orogen, forming a continental suture. The Himalayan orogen is a recent example, with activity continuing today.

Supercontinent Cycle

Over hundreds of millions of years, supercontinents are formed and reformed in a cycle of formation, dispersal, and convergence. Wiggly dashes show collision orogens that accumulate around and between the continents.

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