How does water cycle through subduction zones?

Subduction zones are the locations of the largest exchange of material from the surface to the deep Earth. As the sinking plate heats up and gets squeezed a large fraction of the incoming water is "sweated off" and added to the overlying mantle where it causes melting. These melts feed volcanoes above which are dangerously explosive. However, currently we have little information on the passage of volatiles through this system, and have been unable to attempt any form of mass balance to estimate how much of it enters the deep interior. Fundamental questions such as: what is the distribution of water in the down-going plate, how is slab dehydration distributed with depth and variable along strike, how does dehydration affect flow in the subduction mantle wedge, and what controls the location of the volcanic arc are unanswered.


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