Prograde Metamorphic Assemblage Evolution during Partial Melting of Metasedimentary Rocks at Low Pressures: Migmatites from

The Mt Stafford area in central Australia preserves a low-pressure greenschist- to granulite-facies regional aureole. The metasedimentary sequence has been divided into five zones from greenschist (Zone 1) to granulite facies (Zone 4) and a zone of hybrid diatexite formed from the introduction of granitic magma into the high-grade migmatites (Zone 5). Melt production was dominated by a series of multivariant biotite breakdown reac-tions, not the univariant reactions suggested by previous studies. Although the three main metasedimentary rock types produced similar amounts of melt at the highest grades, their melt produc-tion histories differed markedly as a function of temperature. Aluminous metapelites produced more melt at lower tempera-tures (Zones 2 and 3), whereas metapsammite and cordierite granofels experienced an additional major melt-producing step at higher temperatures (upper Zone 3 and Zone 4). Thi