Mg–Fe distribution between coexisting garnet and biotite, and the status of fibrolite in the andalusite–staurolite zone of the Mt Lofty Ranges, South Australia

Summary The distribution of Fe and Mg between coexisting garnet and biotite from andalusite-staurolite zone rocks of the Mt Lofty Ranges is briefly discussed. The average value of the corresponding distribution coefficient, and those of some related parameters, are compared with the values proposed by a number of authors as being characteristic of certain metamorphic grades. From these comparisons it is concluded that despite their occurrence in a terrain in which fibrolite commonly occurs, the rocks have probably only experienced P-T conditions corresponding to those of the andalusite phase field, and that fibrolite has formed under similar conditions.