Kinetics of crystal dissolution and rock melting: A theoretical and experimental study.

摘要

Rock melting is a process by which rocks are transformed to a partially or totally molten state, usually realized by crystal dissolution at grain boundaries. Thus it is a collective process of crystal dissolution which may include three component processes: interface reaction, diffusion and complications due to convection. Results of numerical calculations demonstrate that interface reaction is not the rate-determining step during non-convective or convective crystal dissolution. Non-convective crystal dissolution experiments at constant temperature show that the "length" of concentration profiles of all components and the dissolution distance are proportional to ;When the rate of partial melting is controlled by diffusion in minerals, the major elements of the melt are always the equilibrium composition dictated by phase equilibria. However, trace element concentrations of the melt during the stationary stage of partial melting will depend on their diffusivities in the coexisting minerals. Therefore major elements and trace elements can be decoupled and incompatible trace element ratios can be fractionated. During partial melting of the mantle beneath the mid-ocean ridges involving a time scale of 1 my, most elements in the pooled melt should be of equilibrium concentration except for components with diffusivities less than 10;Laboratory experiments also illustrate the complexity of the diffusion process. Uphill diffusion is commonly observed, especially during olivine dissolution into andesitic melt. These results suggest caution is necessary in applying least squares mass balance analysis to rocks produced by processes involving chemical diffusion.