Rayleigh fractionation of heavy rare earths and yttrium during metamorphic garnet growth

We present laser-ablation microprobe inductively coupled-mass spectrometry analyses of Y, Yb, Er, Dy, and Gd in garnet crystals from high-grade metamorphic and migmatitic rocks from the Sierras Pampeanas of Argentina. These rocks contain large garnet porphyroblasts ([greater than or equal to] 4 mm) that are compositionally zoned. Rare earth element concentrations in the rims are typically one order of magnitude lower than those in the cores. A notable feature of this zonation is the inversion of Yb/Er and Yb/Dy ratios, from >1 in the cores to Keywords: Rayleigh fractionation, garnet, heavy rare earth clements, melting.