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

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.

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