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

The Palmer Granite is a small, regionally conformable body whichoccurs in association with migmatites and high-grade schistsand gneisses in the metamorphic belt flanking the eastern MountLofty 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-temperaturetroughs for the corresponding synthetic systems and hence itis probable that the granite was produced by crystal-liquidequilibrium. 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 countryrocks are all higher than this. The age is 49015 m.y. Chemical, isotopic, and mineralogical data rule out the possibilityof either granitization, partial melting, or complete meltingof country rocks similar to those analysed. The granite is consideredto have been produced at greater depths. The absence of superimposedcontact aureoles, together with macroscopic and microscopicfabric data, indicates that the Palmer Granite was intrudedduring metamorphism and that it cooled, and in part recrystallized,in the same stress field as that which produced the fabric ofthe country rocks. The metamorphic textures are a result ofthis recrystallization