THE TRANSITION FROM POROUS TO CHANNELIZED FLOW DUE TO MELT ROCK REACTION DURING MELT MIGRATION/

The effect of melt/rock reaction on the mechanisms and kinetics of mel t migration is investigated through a series of melt migration experim ents in which melt saturated only in olivine infiltrates synthetic per idotites containing different proportions of olivine and Ca-poor pyrox ene. The microstructures that develop are significantly different from those formed during melt migration in a chemically equilibrated syste m. A reaction zone develops in which all pyroxene is dissolved, the me lt fraction is increased, and olivine grain size is increased. The rea ction front is unstable so that finger-like structures or channels wit h higher melt content develop. The morphology of the instability depen ds on the initial pyroxene content of the infiltrated rock. This react ive-infiltration instability with the resulting formation of melt fing ers could facilitate the transition from porous to channelized flow in the mantle.