plate tectonics Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

, slab detachment or slab break-off may occur during continent-continent or

arc-continent A continental arc is a type of volcanic arc occurring as an "arc-shape" Topography, topographic high region along a continental margin. The continental arc is formed at an active continental margin where two tectonic plates meet, and where one plat ...

collisions. When the

continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental marg ...

of the subducting plate reaches the

oceanic trench Oceanic trenches are prominent, long, narrow topography, topographic depression (geology), depressions of the seabed, ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers ...

of the

subduction zone Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

, the more buoyant

continental crust Continental crust is the layer of igneous, metamorphic, and sedimentary rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as '' continental shelves''. This layer is sometimes called '' si ...

will in normal circumstances experience only a limited amount of subduction into the asthenosphere. The slab pull forces will, however, still be present and this normally leads to the breaking off or detachment of the descending slab from the rest of the plate. The isostatic response to the detachment of the downgoing slab is rapid uplift. Slab detachment is also followed by the upwelling of relatively hot

asthenosphere The asthenosphere () is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at a depth between c. below the surface, and extends as deep as . However, the lower boundary of the asthenosphere i ...

to fill the gap created, leading in many cases to

magmatism Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of ...

. The uncritical use of the slab-detachment model to explain disparate observations of magmatism, uplift and exhumation in continental collision zones has been criticised.

Slab tears

Detachment initiates at a particular point on the slab and will then propagate laterally along the descending slab, forming a slab tear. The propagation of the detachment will be accompanied by lateral migration of both the associated uplift and the magmatism. Such laterally propagating tears have been recognised from several collision zones, such as the

Hindu Kush The Hindu Kush is an mountain range in Central Asia, Central and South Asia to the west of the Himalayas. It stretches from central and eastern Afghanistan into northwestern Pakistan and far southeastern Tajikistan. The range forms the wester ...

part of the Himalayan Belt. The Tertiary magmatism in the

Alps The Alps () are some of the highest and most extensive mountain ranges in Europe, stretching approximately across eight Alpine countries (from west to east): Monaco, France, Switzerland, Italy, Liechtenstein, Germany, Austria and Slovenia. ...

observed along the Insubric Line has been argued to result from a rapidly propagating slab tear following continental collision and the initiation of slab breakoff.

Slab tears

References

Further reading