Figure 10. Partial melting modeling of the rare-earth elements (REE) of the silicic flows from the Middle Series at Site 917. The models assume nonmodal batch melting and uses partitioning coefficients from Martin (1987). The source is assumed to be hydrated and metamorphosed basalt or gabbro (amphibolitic: 26% plagioclase, 3% quartz, 71% amphibole; metagabbroic/basaltic: 35% plagioclase, 3% quartz, 48% amphibole, 14% augite). The model calculations, all shown at 20% melting, are given for a range of trace-element compositions based on the average concentration of depleted mafic xenoliths of lower-continental origin (in table 6 of Rudnick and Fountain, 1995). The modeling is shown for average mafic xenoliths without enrichment, average mafic xenoliths enriched by 25% REE, and average mafic xenoliths enriched by 100% REE. The REE normalization values are from Sun and McDonough (1989). A. The two Middle Series flow units referred to in the calculations (Fitton et al., 1998a; Units 47 and 55). "Crustal mafic xenolith" is the average of contin-ental mafic xenoliths compiled by Rudnick and Fountain (1995). B. Modeling assuming the melting reaction quartz + plagioclase + amphibole = clinopyroxene + melt. The melting proportions were set at 0.85 amph, 0.41 pl, 0.04 q, and -0.30 cpx. Melting modes for garnet-free melting are based on Rushmer (1991) and Sen and Dunn (1994). The restite produced at 20% melting is 20% pl, 13% cpx, 3% q, and 64% amph. C. Modeling assuming the melting reaction quartz + plagioclase + amphibole = clinopyroxene + garnet + melt with melting proportions taken from Sen and Dunn (1994, equation 5). The restite at 20% melting is 24% grt, 15% pl, 34% cpx, and 27% amph. D. Modeling assuming a metagabbroic source mode and the same melting reactions as Figures 9B and 9C (garnet-free and garnet-bearing restite). The restite at 20% melting for the garnet-free reaction is 34% pl, 25% cpx, 2% q, and 39% amph and for the garnet-bearing restite 27% pl, 49% cpx, 23% grt, and 1% amph.