Abstract
In order to constrain the large ion lithophile (LIL) element distribution for subduction-zone environments, exchange coefficients
Assuming a one-step model of perfect Rayleigh fractionation for continuous decomposition of phengite during subduction, varying alkali ratios observed for island-arc basalts as a function of slab depth may be explained by the LIL-fractionation behavior between fluids and phengites determined in this study. Our data indicate that previously derived models for metasomatic mass transfer during subduction processes need to be reconsidered.