Wilson cycle

Opening and closing of the ocean basin is known as Wilson cycle.


Source discription_ K.C. Condie.

1. Amit K. Mishra Assistant Professor Department of Geology Banasthali University

2. As the concept of sea floor spreading gained acceptance in the late 60's, the consequences for geology gradually began to dawn. One of the first to recognise how plate tectonics could be applied to the geological record was J. Tuzo Wilson. If continents rift apart to form ocean basins, other oceans must close. This may be repeated throughout Earth history. Example: the IAPETUS ocean between England & Scotland in the Lower Palaeozoic, closed in the Caledonian; later opening of the Atlantic, almost in the same place. The cycle is known as the Wilson Cycle:

3. The earliest stage, called the  embryonic stage , involves uplift and crustal extension of continental areas with the formation of rift valleys (e.g. the East African Rift System). This satellite view (this photo, looking south from the Nile delta) shows the young ocean basin of the Red Sea.  The oldest seafloor rocks in the Red Sea are about five million years old, indicating that the Red Sea began to form at that time. 

4. The  young stage  involves the evolution of rift valleys into spreading centers with thin strips of ocean crust between the rifted continental segments. The result is a narrow, parallel-sided sea, for example the Red Sea that is opening between NE Africa and Arabia. This satellite view ( photo, looking south from the Nile delta) shows the young ocean basin of the Red Sea.  The oldest seafloor rocks in the Red Sea are about five million years old, indicating that the Red Sea began to form at that time. 

5. The  mature stage  is exemplified by widening of the growing basin and its continued development into a major ocean flanked by continental shelves and with the continual production of new, hot, oceanic crust along the ridge system (e.g. Atlantic Ocean).

6. Eventually, this expanding system becomes unstable and, away from the ridge, the oldest oceanic lithosphere sinks back into the asthenosphere, forming an oceanic trench subduction system with a Wadati-Benioff zone marking the descending plate and associated island arcs, such as the situation in the western Pacific Ocean, or Andean-type volcanism. The onset of subduction at the ocean boundary marks the subduction stage  of the cycle (e.g. the Pacific Ocean).

7. Once subduction outpaces the formation of new crust at the constructive boundary, the ocean begins to contract. Island arc complexes, complete with their inventory of sedimentary and volcanic rocks, collide and create young mountain ranges around the periphery of the contracting ocean. These features mark the  terminal stage  of the cycle (e.g. the Mediterranean).

8. The  end stage  occurs once all the oceanic crust between the continental masses has subducted, and the continents converge along a collision zone characterised by an active fold mountain belt, such as the Himalayas. Finally the plate boundary becomes inactive, but the site of the join, or suture, between the two continental masses is a zone of weakness in the lithosphere that has the potential to become the site of a new rift and so the cycle continues.