Corona textures between kyanite, garnet and gedrite in gneisses from Errabiddy, Western Australia

Abstract Corona textures, which developed in alternating layers in rocks in a supracrustal belt at Errabiddy, Western Australia, involved:
(a) The production of staurolite, cordierite and quartz or sapphirine between Kyanite and/or sillimanite and gedrite; and
(b) The production of cordierite between garnet and gedrite.
These textures are inconsistent with development along the same pressure–temperature path in the system FeO–MgO–Al₂O₃–SiO₂–H₂O, but can be accounted for if CaO, mainly in garnet, is taken into account. The sapphirine-bearing kyanite–gedrite textures are explained by lower a (SiO₂) during their development. The assemblages indicate a consistent pressure–temperature ( P–T ) trajectory involving substantial uplift with only a slight decrease in temperature. The history of these rocks includes reheating of originally high-grade rocks that had cooled to a stable conductive geotherm, followed by substantial, essentially isothermal uplift. The tectonic environment for this was presumably the one responsible for emplacement of the high-grade terrain in the upper crust.