The Mechanism of Supercontinent Assembly and Breakup

The Wilson Cycle: Plate Tectonics and Supercontinent Formation

The Wilson Cycle, named after geologist John Tuzo Wilson, describes the cyclical process of integrating the pace of geological time and the merging and breaking apart of tectonic plates and continents.

Initiation of the Cycle: Continental Breakup

The Wilson Cycle begins with the breakup of a continent, typically due to the action of a hot spot. This hot spot forms beneath the continent, often attributed to poor 'ventilation' (heat dissipation) in the underlying mantle. This focused heat produces thinning and fracturing of the lithosphere.

A rift then appears, which will evolve into an ocean basin. The floor of this ocean is formed by parallel bands of basalt that reflect Earth's magnetic reversals.

Ocean Basin Development and Passive Margins

The continents on both sides of the rift develop into passive margins, characterized by low seismic activity and significant sedimentation. The oceanic crust will cool as it moves away from the ridge, becoming more rigid and dense.

Subduction and Ocean Closure

When the oceanic crust is cold enough, it will break and begin the process of subduction at its weakest part (closest to the mainland). This generates an oceanic trench, through which the oceanic crust is destroyed.

As the ocean basin closes, the continental crust tends to converge, causing a collision. This collision results in the folding of continental margin sediments and fracturing of the continental edge, leading to significant mountain building.

Supercontinent Formation

This process results in the merging and suturing of tectonic plates, forming a large continent. The suture zone, however, remains a weaker scar. On this great continent, a new hot spot will eventually appear, initiating the breakup phase again.

According to this scheme, rocks from modern oceanic crust, in addition to other continents, will merge around an ancient continental core.

Critiques of the Wilson Cycle Model

Some geologists view this cycle as a model rather than a strict reality, suggesting that major supercontinents are not joined simultaneously. Instead, continental fragments are added and broken up at different, though often close, moments in Earth's history.

We recall that hot spots can occur under the oceanic crust, and not necessarily only under the larger continents or at their center, where less cooling exists. Currently, the most active hot spots include those in the Canary Islands, Cape Verde, and Yellowstone Park.

It is possible that while one part of a continent is breaking apart, another is being added. Furthermore, while one plate is colliding with another, a new rift might be forming internally within one of those plates, leading to further separation.

This dynamic process is currently observed in the African Plate, which is being pulled away along the Indian Ridge while also spreading along the Rift Valley, pushing Africa toward the Indian Ocean. While the Wilson Cycle provides a crucial framework, it perhaps gives undue importance to the role of continents alone.

Unresolved Theoretical Problems

The main problem that the theory does not fully resolve is the precise mechanism driving the convective currents—the irregularities in the mantle or core that cause localized temperature anomalies (higher or lower) compared to their surroundings, leading to the formation of hot spots.