Constraining the presence of amphibole and mica in metasomatized mantle sources through halogen partitioning experiments

Flemetakis S, Klemme, Stracke A, Genske F, Berndt J, Rohrbach A

Abstract

We present experimentally determined partition coefficients (Dmin/melt) for F and Clbetween pargasite (amphibole), phlogopite (mica), clinopyroxene and basanitic melts.All experiments were performed at 1.4 GPa and temperatures between 1015°C and1250°C to simulate fractionation of halogens during melting of metasomatized mantle.The water content of all starting materials was 16 wt.% to promote crystallization ofamphibole and mica. The halogen content of all starting mixtures was 0.45 wt.% for Fand 0.61 wt.% for Cl. Our data show that F is compatible (D > 1) in pargasite andphlogopite, while Cl is strongly incompatible (D < 0.1) in both phases. Theexperimentally derived partition coefficients allow to quantitatively constrain theamounts of mica- and amphibole in metasomatized spinel-lherzolite sources from theobserved halogen and rare earth element contents in derivative melts. Calculated F/Cland F/Nd values of melts from different mantle sources, ranging from depleted to fertileand metasomatized mantle, are compared to those of melt inclusions from basalts frommid ocean ridges, ocean islands, and arc and intra-plate continental settings. Ourresults suggest that, depending on the tectonic setting, F/Cl and F/Nd of meltinclusions can be used to determine the presence and the amount of amphibole andmica in different mantle sources, and thus allow distinguishing between melting ofnominally anhydrous and volatile-rich mantle sources.