Editing Asthenosphere (section)

==Origin==
The mechanical properties of the asthenosphere are widely attributed to the partial melting of the rock.{{sfn|Kearey|Klepeis|Vine|2009|p=49}} It is likely that a small amount of melt is present through much of the asthenosphere, where it is stabilized by the traces of volatiles (water and carbon dioxide) present in the mantle rock.{{sfn|Hirschmann|2010}} However, the likely amount of melt, not more than about 0.1% of the rock, seems inadequate to fully explain the existence of the asthenosphere. This is not enough melt to fully wet grain boundaries in the rock, and the effects of melt on the mechanical properties of the rock are not expected to be significant if the grain boundaries are not fully wetted. The sharp lithosphere-asthenosphere boundary is also difficult to explain by partial melting alone.{{sfn|Karato|2012}} It is possible that the asthenosphere is a zone of minimum water solubility in mantle minerals so that more water is available to form greater quantities of melt.<ref>{{cite journal |last1=Mierdel |first1=Katrin |last2=Keppler |first2=Hans |last3=Smyth |first3=Joseph R. |last4=Langenhorst |first4=Falko |date=19 January 2007 |title=Water solubility in aluminous orthopyroxene and the origin of Earth's asthenosphere |journal=[[Science (journal)|Science]] |volume=315 |issue=5810 |pages=364–368 |bibcode=2007Sci...315..364M |doi=10.1126/science.1135422 |pmid=17234945 |s2cid=33006157}}</ref> Another possible mechanism for producing mechanical weakness is grain boundary sliding, where grains slide slightly past each other under stress, lubricated by the traces of volatiles present.{{sfn|Karato|2012}} Weakening below oceanic plates is partly caused by their motion itself, thanks to the non-linear dislocation creep mechanism.{{sfn|Patočka|Čížková|Pokorný|2024}}

Numerical models of mantle convection in which the viscosity is dependent both on temperature and strain rate reliably produce an oceanic asthenosphere, suggesting that strain-rate weakening is a significant contributing mechanism,<ref>{{cite journal |last=Becker |first=Thorsten W. |date=November 2006 |title=On the effect of temperature and strain-rate dependent viscosity on global mantle flow, net rotation, and plate-driving forces |journal=[[Geophysical Journal International]] |volume=167 |issue=2 |pages=943–957 |bibcode=2006GeoJI.167..943B |doi=10.1111/j.1365-246X.2006.03172.x |doi-access=free }}</ref> and explaining the particularly weak asthenosphere below the Pacific plate.{{sfn|Patočka|Čížková|Pokorný|2024}}