Reactive infiltration of hydrous melt above the mantle transition zone
نویسندگان
چکیده
[1] Seismic studies repeatedly image a low‐velocity layer overlying the mantle transition zone in tectonic settings ranging from subduction zones to continental cratons. This layer has been hypothesized to result from the presence of a dense partial melt formed by dehydration melting as relatively wet transition zone material is advected by convection currents into the low‐water‐solubility upper mantle. Here we examine this hypothesis by considering the dynamic infiltration of a low‐viscosity reactive hydrous melt into a high‐viscosity ambient solid. The thickness of the melt layer is strongly controlled by return flow induced in the surrounding viscous solid, and in steady state a dynamic equilibrium is achieved where the melt lens is restrained from collapse by the exterior mantle. Melt layers with thicknesses in excess of 10 km develop for a wide range of mantle parameters and develop on timescales equivalent to the lifespan of an ocean basin.
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On the dynamics of a hydrous melt layer above the transition zone
[1] The ‘‘transition zone water filter’’ (Bercovici and Karato, 2003) model relies on the presence of a dense hydrous melt above the 410-km discontinuity that is formed by dehydration melting as wet wadsleyite undergoes a phase change to low-water-solubility olivine. Recent studies suggest that, particularly in the Pacific, there is sufficient water in the transition zone for dehydration meltin...
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