Mafic intrusions in southwestern Australia related to supercontinent assembly or breakup?

Variably oriented dolerite intrusions outcrop in the Albany-Fraser Orogen along the south coast of Western Australia with previously unknown ages but where previous studies interpreted Mesoproterozoic to Cretaceous emplacement. Here, we place temporal constraints on seven mafic intrusions across similar to 150 km of coast using zircon U-Pb, apatite U-Pb, and plagioclase 40Ar/39Ar geochronology, coupled with whole-rock major and trace-element geochemistry, that reveal late Mesoproterozoic to potentially Early Cretaceous crystallisation ages. Three intrusions metamorphosed to greenschist facies are likely associated with either the emplacement of the ca 1210 Ma Marnda Moorn large igneous province or Stage II Albany-Fraser Orogeny, both of which were associated with the assembly of Rodinia. Three unmetamorphosed dykes have (probable) Neoproterozoic to lower Cambrian emplacement ages, likely associated with the ca 550-500 Ma Kuunga Orogeny during Gondwana assembly. The final sill, also unmetamorphosed, strikes perpendicular to the other six intrusions, shows unusual Pb anomalies and contains inherited zircon that has been reset by a Permian or younger event, pointing towards magmatism in southwestern Australia during the breakup of Gondwana. The new results provide hitherto unrecognised mafic intrusive evidence for modification of Proterozoic crust, potentially associated with Rodinia assembly, Gondwana assembly and Gondwana breakup in southwestern Australia.

Automated summary

This study in the Albany-Fraser Orogen of Western Australia placed temporal constraints on seven mafic intrusions, revealing late Mesoproterozoic to potentially Early Cretaceous ages and suggesting associations with previous geological events. The new results provide evidence for modification of Proterozoic crust, potentially linked to Rodinia assembly, Gondwana assembly, and Gondwana breakup in southwestern Australia.