Geology makes it possible to subduct into an intransitive verb and a reflexive verb. The bottom plate itself is the theme. It subducts in the direction of retract or retreats and is therefore the “subduction plate”. In addition, the word plate is specifically attached to the “subduction plate”, although the upper plate is also a plate in English. [79] The top plate remains stuck, so to speak. To put it simply, geology has to switch to another verb, usually crush. The upper disk, the subject, performs the action of overwriting the object, the lower disk which is overwritten. [80] The lithosphere-asthenospheric boundary (LAB[18][19]) is relatively sharp and probably coincides with the onset of partial fusion or a change in composition or anisotropy. [20] Different definitions of border reflect different aspects of the border area. In addition to the mechanical boundary defined by the seismic data, which reflects the transition from the rigid lithosphere to the ductile asthenosphere, this includes a thermal boundary layer above which heat is conducted by thermal conduction and below which heat is largely conducted by convection; a rheological limit at which the viscosity falls below about 1021 Pa-s; and a chemical boundary layer above which the mantle rock is depleted of volatile substances and enriched with magnesium relative to the underlying rock. [21] Arc magmatism occurs one hundred to two hundred kilometers from the trench and a hundred kilometers above the subduction plate. This generation of arc depth magma is the result of the interaction between the aqueous liquids released by the subduction plate and the corner of the arc envelope, which is hot enough to melt with the addition of water. [62] It has also been suggested that mixing of liquids from a subducted tectonic plate and molten sediments already occurs at the top of the plate before mixing with the mantle occurs.

[63] . to the sea, which causes the trench to “recede” on the laxative plate, or it can serve as a “sea anchor” by remaining fixed relative to the top of the subduction plate. In the latter case, the enlargement of the basin forces the posterior part of the overlying layer…n The age of the oceanic crust can be used to estimate the thickness (thermal) of the lithosphere, where the young oceanic crust has not had enough time to cool the underlying mantle, while the older oceanic crust has a thicker mantle lithosphere below. [19] The oceanic lithosphere subdues to what are called convergent boundaries. These boundaries may exist between the oceanic lithosphere on one plate and the oceanic lithosphere on another plate, or between the oceanic lithosphere on one plate and the continental lithosphere on another plate. In the second situation, the oceanic lithosphere always subdued because the continental lithosphere is less dense. The subduction process consumes older oceanic lithospheres, so the oceanic crust is rarely more than 200 million years old. [20] The process of formation and destruction of supercontinents by repeated cycles of formation and destruction of oceanic crust is known as the Wilson cycle. The arc trench complex is the surface expression of a much deeper structure. Although not directly accessible, deeper sections can be studied using geophysics and geochemistry. Subduction zones are defined by an inclined earthquake zone, the Wadati-Benioff zone, which descends from the trench and extends to the 660-kilometre discontinuity.

Subduction zone earthquakes occur at greater depths (up to 370 miles (600 km)) than elsewhere on Earth (typically less than 12 miles (20 km) deep); Such deep earthquakes can be caused by deep phase transformations, thermal runaway or dehydration embrittlement. [25] [26] Seismic tomography shows that some plates can penetrate the lower mantle[27][28] and sink to the core-mantle boundary. [29] Here, plate residues can eventually heat up to such an extent that they rise to the surface as mantle plumes. [30] [31] The upper part of the asthenosphere is thought to be the area where the large, rigid and brittle lithospheric plates of the Earth`s crust move. Due to the temperature and pressure conditions in the asthenosphere, rocks become ductile and move at deformation rates measured in cm/year over linear distances that eventually measure thousands of kilometers. In this way, it flows like a convection stream and radiates heat from the Earth`s interior to the outside. Above the asthenosphere, the rock behaves elastically at the same rate of deformation and, because it is fragile, can break, causing faults. The rigid lithosphere is thought to “float” or move over the slow-flowing asthenosphere, allowing isostatic equilibrium[13] and allowing tectonic plates to move. [14] [15] Subduction zones were also considered as possible repositories of nuclear waste, where subduction itself would transport the material into the planetary mantle, safe from any possible impact on humanity or the surface environment. However, this type of disposal is currently prohibited by international agreements. [83] [84] [85] [86] In addition, plate subduction zones are associated with very large megashocks, making the effects of using a particular site for disposal unpredictable and potentially detrimental to the safety of long-term disposal.

[84] The largest volcanic rocks on the seafloor are mid-ocean ridge basalts, which originate from potassium-poor tholeiitic magmas. These rocks have low concentrations of large ionic lithophilic elements (LILE), light rare earth elements (LREE), volatile elements and other highly incompatible elements. There is basalt enriched with incompatible elements, but they are rare and associated with Mid-Ocean Ridge hotspots such as the vicinity of the Galapagos Islands, the Azores and Iceland. [15] I waited another three months impatiently, and then sent him back to the same position to see if there could be a response.