Melting, dehydration, and the dynamics of off-axis plume-ridge interaction

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We present results from a series of two-dimensional numerical experiments in which a thermally buoyant, off-axis mantle plume interacts with a nearby ridge axis. These experiments incorporate melting and a number of related dynamical feedbacks, including energy loss to latent heating and Fe depletion buoyancy as well as viscosity increases due to dehydration during melting. Results indicate that dehydration, which acts to increase the viscosity of the residual mantle during melting, profoundly impacts the morphology of flow between plume and ridge axis. As upwelling plume material begins to melt, it becomes significantly more viscous and readily accretes to the overlying lithosphere. This creates a viscous plug that grows downward from the base of the lithosphere directly above the plume conduit. Plume material traveling to the ridge axis is then deflected horizontally at subsolidus depths by this plug, allowing pristine, unmelted plume material to reach the ridge axis. Experiments without dehydration show that the loss of thermal energy to latent heating during melting marginally decreases the flow of plume material along the base of the lithosphere to the ridge axis. Alternatively, extraction of Fe from the solid during melting slightly increases plume flow to the ridge. These results also demonstrate that the flow of plume material to the ridge axis is sensitive to the slope of the base of the rheological lithosphere, consistent with previous studies of off-axis plume ridge interaction. © 2003 by the American Geophysical Union.

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Geochemistry, Geophysics, Geosystems