High-pressure experimental melting studies on a pelitic composition with 2 and 5 percent by weight of added water demonstrate that cordierite, quartz, biotite, sillimanite, and plagioclase are important residual phases coexisting with granitic liquid at 4 kb and are joined by garnet at 7 kb. At 10 kb, garnet quartz, biotite, sillimanite, and plagioclase constitute the residuum coexisting with granitic liquid.

Compositions of residual phases and their Mg-Fe partition relationships compare closely with phases from cordierite- and garnet-bearing granitic rocks in eastern Australia and strongly support geochemical arguments that this particular granitic suite is derived by partial melting of pelitic sediments. Thus, the cordierite-bearing granitic rocks were probably derived by partial melting of pelite at >25-km depth, whereas the garnet-bearing granites were derived at ≿25-km depth.

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