Evidence for a 1750–1710 Ma orogenic event, the Wonga Orogeny, in the Mount Isa Inlier, Australia: Implications for the tectonic evolution of the North Australian Craton and Nuna Supercontinent

Abstract

In this contribution we propose that Mount Isa Inlier was affected by a new orogeny, the Wonga Orogeny, which occured between 1750 and 1710 Ma. Evidence for this event is principally given by structural field data and geochronology from this study and that documented in Spence et al. (2021). In this study, field relationships and geochronology within the Duchess Belt of the Mary Kathleen Domain reveals two main deformation events during the Wonga Orogeny, here D1 and D2. The former produced predominantly upright, tight, east–west trending folds whereas the latter produced upright to overturned, north–south trending folds. D1 can be constrained between 1741 ± 6 Ma to 1736 ± 3 Ma, based on the U-Pb magmatic zircon ages of the Revenue granite which intrudes prior to or early during D1 and the intrusion of the Overlander granite which has not been affected by D1. The age of the D2 event can be constrained between 1736 ± 3 Ma and 1722 ± 7 Ma based on the U-Pb magmatic zircon ages of the Overlander granite which intrudes prior to or early during D2 and the Myubee granite which intrudes syn-D2 – within the fold hinge of an F2 anticline. These timing relationships coupled with F2 folds associated with mineral lineations (L2) defined by biotite and hornblende, as well as syn-D2garnet, kyanite and sillimanite porphyroblastssuggest that amphibolite-facies metamorphism, deformation andcontemporaneous magmatism defined by the Wonga and Burstall Suite magma’s all occured between 1750 and 1710 Ma. These characteristics typically define orogenesis and is here, accordingly proposed as a third orogenic event within the Mount Isa Inlier. These findings have implications on the tectonic evolution of the North Australian Craton and Nuna Supercontinent.