Abstract
The dissolution rates of the major upper mantle minerals olivine, orthopyroxene, clinopyroxene, spinel, and garnet have been determined in an alkali basalt melt at superliquidus temperatures and 5, 12, and 30 kb. At low pressure where olivine is the liquidus phase of the basalt, olivine has a slower dissolution rate than clinopyroxene; however, at higher pressure where clinopyroxene is the liquidus phase, clinopyroxene has a slower dissolution rate than olivine. The relative rates of dissolution of olivine and clinopyroxene at each pressure are, therefore, governed by their relative stabilities in the melt and hence by the structure of the melt. As the degree of superheating above the liquidus increases at each pressure, the dissolution rates of olivine and clinopyroxene converge, suggesting that the melt undergoes temperature-induced structural changes.

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