The Palmer Granite--A Study of a Granite within a Regional Metamorphic Environment

The Palmer Granite is a small, regionally conformable body which occurs in association with migmatites and high-grade schists and gneisses in the metamorphic belt flanking the eastern Mount Lofty Ranges of South Australia. Seven new rock analyses, including some trace element data, are presented. The normative percentages of quartz-orthoclase-albite, and orthoclase-albite-anorthite fall near or within the low-temperature troughs for the corresponding synthetic systems and hence it is probable that the granite was produced by crystal-liquid equilibrium. Mineral data on biotites (2 analyses) and potassium feldspars (7 analyses) indicate disequilibrium with the envelope rocks. Initial S7Sr/86Sr ratios for the granite specimens average 0-708, whereas the initial 87Sr/86Sr ratios of the analysed country rocks are all higher than this. The age is 490±15 m.y. Chemical, isotopic, and mineralogical data rule out the possibility of either granitization, partial melting, or complete melting of country rocks similar to those analysed. The granite is considered to have been produced at greater depths. The absence of superimposed contact aureoles, together with macroscopic and microscopic fabric data, indicates that the Palmer Granite was intruded during metamorphism and that it cooled, and in part recrystallized, in the same stress field as that which produced the fabric of the country rocks. The metamorphic textures are a result of this recrystallization