Extension during the Liebig Orogeny: Revised tectonic setting of Paleoproterozoic central Australia

Abstract

Magnetotelluric imaging of a lithospheric-scale boundary in central Australia has been used to support a model of collision between the North Australian Craton and an exotic continental ribbon referred to as the Warumpi Province during the late Paleoproterozoic Liebig Orogeny (c. 1640 Ma). This idea of collision has become an important element to reconstructions of late Paleoproterozoic Australia. In this study, we present mineral equilibria forward models from c. 1640 Ma metamorphic rocks to delineate the thermal regime associated with the Liebig Orogeny. Liebig-aged cordierite–orthopyroxene–biotite–quartz–plagioclase–K-feldspar–ilmenite–magnetite assemblages constrain peak metamorphic conditions to 4–5 kbar and 770–800 °C. These conditions are indicative of a high geothermal gradient regime and the mineral assemblage evolution shows no evidence for significant pressure changes that would generally support a crustal thickening model. Detrital zircon age spectra for the metasediments in the assumed exotic crust are broadly similar to the age record in the Aileron Province in the southern part of the North Australian Craton. Furthermore, εNd and εHf isotopic data of Liebig-aged granitic rocks make it permissible that they are derived from melting of North Australian Craton crust. This suggests the Warumpi Province was not exotic to the North Australian Craton and was instead a part of it. On the basis of the shared history between the Warumpi and Aileron Provinces and the newly constrained thermal character of c. 1640 Ma metamorphism, we suggest the Liebig Orogeny was characterised by extensional deformation of the North Australian Craton in the upper plate above a southward retreating subduction system. Tectonically, the Liebig Orogeny is interpreted to record a back-arc regime characterised by sedimentation, mafic and felsic magmatism, and predominantly contact metamorphism, and represents the continuation of a long-lived (c. 200 Ma) upper plate system that dictated the evolution of the North Australian Craton during the late Paleoproterozoic.