Mg-Fe fractionation in metamorphic environments.

Abstract

The Fe-Mg distribution between a fluid phase and a coexisting solid solution is examined. Judging from fluid-inclusion data, many metamorphic fluids are dominated by chloride and chloride complexes. A set of mineral-fluid exchange diagrams have been constructed, for 600oC and 1 kbar, where the fluid is a chloride-rich aqueous solution. The intensity of the Mg preference of the silicates decreases as follows (with numbers in parentheses the preferred KD values for 600oC): cordierite (20.8) > biotite (11.1) > clinopyroxene (10.7) > olivine (8.3) > hornblende (6.6-5.0) approx orthopyroxene (5.4) > garnet (2.2). More data on metamorphic fluids are needed.-R.A.H.