In
plate tectonics
Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...
, 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" 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 plate has conti ...
collisions. When the
continental margin of the subducting plate reaches the
oceanic trench
Oceanic trenches are prominent long, narrow topographic depressions of the ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about of oceanic tren ...
of the
subduction zone
Subduction is a geological process in which the oceanic lithosphere is Geochemical cycle, recycled into the Earth's mantle at convergent boundary, convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less d ...
, the more buoyant
continental crust
Continental crust is the layer of igneous, sedimentary, and metamorphic 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 ''sial'' bec ...
will in normal circumstances experience only a limited amount of subduction into the asthenosphere. The
slab pull
Slab pull is a geophysical mechanism whereby the cooling and subsequent densifying of a subducting tectonic plate produces a downward force along the rest of the plate. In 1975 Forsyth and Uyeda used the inverse theory method to show that, of the ...
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 ~ below the surface, and extends as deep as . However, the lower boundary of the asthenosphere is not ...
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 part of the Himalayan Belt.
The Tertiary magmatism in the
Alps
The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Sw ...
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.
References
Further reading
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*{{cite journal , last1=Lee , first1=Hao-Yang , last2=Chung , first2=Sun-Lin , last3=Lo , first3=Ching-Hua , last4=Ji , first4=Jianqing , last5=Lee , first5=Tung-Yi , last6=Qian , first6=Qing , last7=Zhang , first7=Qi , title=Eocene Neotethyan slab breakoff in southern Tibet inferred from the Linzizong volcanic record , journal=Tectonophysics , date=1 November 2009 , volume=477 , issue=1 , pages=20–35 , doi=10.1016/j.tecto.2009.02.031 , bibcode=2009Tectp.477...20L , url=http://ntur.lib.ntu.edu.tw//handle/246246/172373
Plate tectonics