View source for Earth:Mantle wedge

{{Short description|Triangular shaped piece of mantle that lies above a subducting tectonic plate}}
A '''mantle wedge''' is a triangular shaped piece of [[Earth:Mantle (geology)|mantle]] that lies above a [[Earth:Subduction|subducting]] tectonic plate and below the overriding plate. This piece of mantle can be identified using seismic velocity imaging as well as earthquake maps.<ref name="Weins 2008">{{cite journal|last=Weins|first=A. D. |author2=Conder, A. J. |author3=Faul H. U.|title=The seismic structure and dynamics of the mantle wedge|journal=Annual Review of Earth and Planetary Sciences|year=2008|doi=10.1146/annurev.earth.33.092203.122633|volume=36|pages=421–455|bibcode=2008AREPS..36..421W }}</ref>  Subducting oceanic slabs carry large amounts of [[Chemistry:Water|water]]; this water lowers the melting temperature of the above mantle wedge.<ref>{{cite journal|last=Kelley|first=K.|author2=Plank, T. |author3=Newman, S. |author4=Stolper, E. |author5=Grove, T. |author6=Parman, S. |author7=Hauri, E. |title=Mantle melting as a function of water content beneath the Mariana arc|journal=Journal of Petrology |year=2010|volume=51|issue=8| pages=1711–1738 |doi=10.1093/petrology/egq036|doi-access=free }}</ref>  Melting of the mantle wedge can also be contributed to depressurization due to the flow in the wedge. This melt gives rise to associated volcanism on the earth's surface. This volcanism can be seen around the world in places such as {{wipe|Japan}} and Indonesia.<ref name="Hirshmann 2012">{{cite journal|last=Hirshmann|first=M. M.|title=Ironing out the oxidation of earth's mantle|journal=Science Magazine|year=2012|volume=10|issue=1126}}</ref>

[[File:Cross-section of a subduction zone and back-arc basin.jpg|thumb]]

==Water in mantle wedge==

Magmas produced in subduction zone regions have high [[Earth:Volatile (astrogeology)#Igneous petrology|volatile]] contents. This water is derived from the breakdown of hydrous minerals in the subducting slab, as well as water in the oceanic plate from percolation of seawater. This water rises from the subducting slab to the overriding mantle wedge. The water lowers the melting temperature of the wedge and leaves behind melt inclusions that can be measured in the associated arc volcanic rocks.<ref name=Keken>{{cite journal|doi=10.1016/S0012-821X(03)00460-6|url=http://www.geo.lsa.umich.edu/~keken/papers/frontiers03/vanKeken_EPSL03.pdf|title=The structure and dynamics of the mantle wedge|year=2003|last1=Van Keken|first1=Peter E|journal=Earth and Planetary Science Letters|volume=215|issue=3–4|pages=323–338|bibcode=2003E&PSL.215..323V|url-status=dead|archiveurl=https://web.archive.org/web/20110721170638/http://www.geo.lsa.umich.edu/~keken/papers/frontiers03/vanKeken_EPSL03.pdf|archivedate=2011-07-21}}</ref><ref>{{cite journal|last=Kimura|first=J.|author2=Yoshida, T.|title=Contributions of slab fluid, mantle wedge and crust to the origin of quaternary lavas in the NE Japan arc|journal=Journal of Petrology|year=2006|volume=47|issue=11|pages=2185–2232|doi=10.1093/petrology/egl041|doi-access=free}}</ref>

==Structure of the mantle wedge==

The [[Earth:Forearc|forearc]] mantle extends from where the subducting slab meets the cold nose of the mantle wedge, this occurs at depths from 10–40&nbsp;km.<ref name="Weins 2008"/>  Low seismic attenuation, and high seismic velocities characterize this region. There is a boundary between this low attenuation region and a high attenuation region on the forearc side of the arc volcanoes.<ref name="Stachnik 2004">{{cite journal|last=Stachnik|first=J. C.|author2=Abers, A. G.|title=Seismic attenuation and mantle wedge temperatures in the Alaska subduction zone|journal=Journal of Geophysical Research|year=2004|volume=10|issue=B10304|doi=10.1029/2004jb003018|bibcode=2004JGRB..10910304S |doi-access=free}}</ref> To image the mantle wedge region below volcanic arcs P-wave, S-wave and seismic attenuation images should be used in coordination. These [[Seismic tomography|tomographic]] images show a low velocity, high attenuation region above the subducting slab. The slowest velocities in these volcanic arc regions are Vp= 7.4&nbsp;km·s<sup>−1</sup> and Vs= 4&nbsp;km·s<sup>−1</sup>.<ref name="Weins 2008"/> Mantle wedge regions that do not have associated arc volcanism do not show such low velocities. This can be attributed to the melt production in the mantle wedge.

==Mantle wedge flow==

Flow in mantle wedges has important effects on the thermal structure, overall mantle circulation and melt within the wedge. [[Earth:Mineral|Mineral]]s are anisotropic and have the ability to align themselves within the mantle when exposed to strain.<ref name="Weins 2008"/>  These mineral alignments can be seen using seismic imaging, as waves will travel through different orientations of a mineral at different speeds. [[Physics:Shear strain|Shear strain]] associated with mantle flow will align the fast direction of [[Chemistry:Pyroxene|pyroxene]] and [[Chemistry:Olivine|olivine]] grains in the direction of flow. This is the most common theory on flow within the mantle, although opposing theories do exist (6){{citation needed|date=March 2012}}. Flow within the mantle wedge is parallel to the crust until it reaches the relatively cooler nose of the wedge, then is overturned and is parallel to the subducting slab. The nose of the wedge is generally isolated from the overall mantle flow.<ref name="Stachnik 2004"/>

==Oxidation in the mantle wedge==

Studies have shown that [[Biology:Magma|magma]]s that produce island arcs are more oxidized than the magmas that are produced at mid-ocean ridges. This relative degree of oxidation has been determined by the iron oxidation state of fluid inclusions in glassy volcanic rocks. It has been determined that this state of oxidation is correlated with the water content of the mantle wedge. Water itself is a poor oxidant and therefore the oxidizing agent must be transported as a dissolved ion in subducting slab.<ref name="Hirshmann 2012"/>

==References==
{{Reflist}}

[[Category:Tectonics]]

{{Sourceattribution|Mantle wedge}}