Delamerian-aged metamorphism in the southern Curnamona Province, Australia: implications for the evolution of the Mesoproterozoic Olarian Orogeny

Monazite electron microprobe U-Th-Pb and garnet Sm-Nd isotopic data from metapelitic assemblages in the Willyama Supergroup in the southern Curnamona Province, south-central Australia, indicate that the terrain underwent regional greenschist to amphibolite-grade metamorphism during the c. 500 Ma Delamerian Orogeny. The Delamerian-aged mineral assemblages include prograde garnet-staurolite and kyanite-bearing associations that overprint andalusite- and sillimanite-bearing assemblages that are interpreted to have developed during the c. 1600 Ma Olarian Orogeny. Importantly, the development of secondary kyanite-bearing assemblages in the southern Curnamona Province has been used previously to suggest that the Olarian Orogeny followed an anticlockwise P-T evolution. If such assemblages are the product of c. 500 Ma metamorphism, then the anticlockwise P-T path is an apparent path, due to the overprint of a distinct metamorphic cycle c. 1100 Ma later. Making such distinctions is therefore extremely important when using the textural and metamorphic evolution of polycyclic terrains to model the thermal behaviour of the crust during orogeny. This study highlights the utility of in situ geochronology, linking age data to petrologically important phases and assemblages.