9406134 Nielsen The goal of the proposed research is to create amphibole- melt experimental data sets at 2, 5, and 8 kb pressure and to calculate expressions describing the parameters that control REE and HFSE partitioning for amphibole. One of the premises of the proposed work is that the systematics of REE and HFSE partitioning in amphibole-melt systems may be similar to those for pyroxene, which were controlled by a combination of factors including phase chemistry, pressure and temperature. Natural compositions, in contrast to synthetic compositions, will be used to provide a data base that is immediately relevant to natural arc basalt and andesite (and possibly alkaline and MORB) systems.