A modified iterative sandwich method for determination of near-solidus partial melt compositions. I. Theoretical considerations

The sandwich technique for determining the composition of partial melts in equilibrium with mantle lithologies may be a particularly powerful method for determining melt compositions at the onset of melting if the method is applied iteratively. However, conventional iterative sandwich experiments, in which the liquid from a preceding experiment is used as the "meat" of the sandwich in the following experiment, may require many iterations before the melts produced can be directly relatable to the melting relations of the target bulk rock composition. A modified iterative sandwich experimental (MISE) technique is proposed that may circumvent many of the problems of more conventional techniques. Consideration of experimental uncertainties, including both random and systematic errors in determination of partial melt compositions as well as the influence of errors in estimates of the solidus temperature of the rock of interest, suggests that the MISE technique may produce robust results even when melt composition errors are significant and that errors in estimation of the solidus location are detectable and therefore avoidable.