Supercontinent cycle

Under Wilson cycle refers to the continuous formation and the subsequent breakup of supercontinents and the continued opening and closing of ocean basins in the context of plate tectonics. The term is named after the Canadian geoscientists John Tuzo Wilson, who has these cycles that occur in time scales of several 100 million years, first described.

Phases

Resting phase

At the beginning of the development is a Wilson ( large ) continental block, which is located in a tectonic quiescence. During this resting phase the fold mountains are removed, have emerged from the final phase of the preceding Wilson cycle.

Trench or Rift - stage

In the resting phase the continental rift stage follows. As the founder of the hotspot hypothesis Wilson voices the suspicion that hotspots are responsible for the breaking of the continental lithosphere and rifting. A hotspot is a region of elevated temperature properties under the mantle. , Such a hotspot is under the oceanic crust, then oceanic volcanic islands can form (for example, the Hawaiian archipelago ). Under a continental bloc active hotspots may cause the crust is thinned and bulged until it finally gives way and collapses sideways dodges ( extensional ). The result is a grave system, such as the East African rift. Along the faults in the earth's crust, there is usually basic volcanism.

Oceanic young stage ( Red Sea stage)

The intra- continental rift has so greatly expanded that the strain can no longer be compensated by the lowering and tilting of the grave edge floes of continental crust and along the expansion joint by rising basaltic magma oceanic crust is formed. Along the expansion, now referred to as Oceanic spreading zone, a mid-ocean ridge (MOR ) is formed. The large continental block has been thus divided into two smaller, drifting apart continental blocks. The young ocean basins facing, now again increasingly tectonically quiet edges of the continental blocks are referred to as passive continental margins. Even before the formation of oceanic crust, the grave zone is often dropped so far that it is below sea level and has been transformed with adequate near the coast, in an estuary.

Oceanic stage of maturity ( Atlantic - stage)

This stage refers to a relatively wide open ocean basin with passive continental margins and MOR, which extends along the longitudinal axis of the basin. Under special circumstances, may be promoted on MOR at times as much magma that he rises above the sea level. The only current example of such a special case is the island of Iceland.

The passive continental margins, now far away from the MOR form shelves on which to deposit thick sediment sequences.

Inversion of the ocean basin ( Pacific stage)

Since the surface of the earth ( ie including the seabed ) does not increase, must, as will be re-formed to MOR crust, disappear elsewhere earth's crust from the surface. This occurs at so-called subduction zones, where oceanic crust beneath the continental crust dives ( subduction ). About the subduction zone produces a volcanic arc and, under certain conditions, even a fold mountains of the Andean type.

Changes in the course of time at least one of the edges of the Atlantic - stage - ocean basin of a passive continental margin in a subduction zone, is, so far as the Subduktionsrate is higher there than the spreading rate at MOR, the ocean basins are gradually narrower as the continental blocks to the edges of the basin now moving towards one another.

The term Pacific stage is a little misleading, as the Pacific, although almost completely flanked by subduction zones, not in danger of being closed. In fact, the Pacific, as a purely morphological pool, very durable and there exists at least since 500 million years (in paleogeographic and tectonic maps usually called Panthalassa ).

Oceanic final stage (Mediterranean - stage)

Continued subduction of oceanic crust of the Pacific -type basin leads, so far as it is faster than the spread of the MOR to the progressive closure of the ocean basin. After subduction of the MOR basin inversion is further accelerated by eliminating the spread. Finally, the continental blocks, which limit the pelvis come into contact. This collision leads to mountain building ( orogeny ) of the collision type ( creation of a so-called alpinotype Fold Mountains ), initially dominate the shifting and folding, which folded the shelf sediments of the ocean basin and the rocks of the volcanic arc and are pushed over each other.

Collision stage ( Himalayan stage)

At this stage the ocean basins is completely closed and the ( alpinotype ) orogeny reached its peak. The Überschiebungstektonik has led to an enormous thickening of the crust involved. The thickened crust area is lifted by mass balancing movements a bit and a high mountain range formed. The continental blocks that were formerly separated by the ocean basins are united now in a larger continental block (upper or supercontinent ).

Resting phase

After the end of the orogeny of the newly formed continental block enters a tectonic dormancy and the towering mountains is removed again. The cycle has reached its starting point.