Petrogenesis of cordierite-orthoamphibole assemblages from the Springton region, South Australia

Abstract

Textural evidence for the partial breakdown of staurolite-biotite and andalusite-biotite assemblages to cordierite-orthoamphibole implies high temperature metasomatic depletion of K2O in semi-pelitic rocks from Springton, South Australia. The origin of the reaction textures is discussed with reference to μK2O-T diagrams derived from the topologically equivalent μK2O-(-μH2O) diagram showing both discontinuous and Fe-Mg continuous reactions. The involvement of fluids in the metasomatic process is implied by the scale of K2O removal and suggests that the outcrop pattern of cordierite-gedrite rocks reflects, at least in part, a heterogeneous distribution of advecting fluids in the metamorphic pi..