New age constraints for the Tommy Creek Domain of the Mount Isa Inlier, Australia

Abstract

The Tommy Creek Domain is a complex, yet little studied, terrane in the Eastern Subprovince of the Mount Isa Province, northwest Queensland Australia. In this study, we take advantage of modern low-cost and rapid geochronology techniques to undertake an iterative dating approach integrated with detailed fieldwork to define the ages and extents of numerous lithologies and units of the Tommy Creek Domain. This includes some units not previously identified, lithologies previously grouped together based on field observations but now shown to have multiple distinct ages and dates not commonly represented in Mount Isan time–space plots. We identify an episode of felsic magmatism at ca 1640 Ma, and multimodal intrusions (ca 1615 Ma) immediately preceding the onset of the Isan Orogeny. A major rock package of the Tommy Creek Domain, the Milo beds, are characterised here as the youngest pre-Isan Orogeny sedimentary unit in the Eastern Subprovince (1660–1620 Ma), confirming that sedimentation and possibly rifting continued after deposition of the Soldiers Cap, Mount Albert and Kuridala groups (ca 1690–1650 Ma) before the onset of the Isan Orogeny (ca 1600 Ma). The Milo beds are thus age equivalent to the Mount Isa and McNamara groups of the Western Succession. There is evidence of a compositional shift in sedimentation coincident with the ca 1640 Ma Riversleigh Inversion event, previously only observed in the Western Subprovince in the Lawn Hill Platform. The application of geochronology as part of the mapping workflow can assist with differentiating geological units in terranes where field evidence is ambiguous and can aid in the focusing of objectives for field campaigns to enable the best possible interpretations to be made. KEY POINTS New ages constrain the Milo beds in the Tommy Creek Domain as the youngest stratigraphy in the Eastern Subprovince of the Mount Isa Province. The Milo beds are age equivalents of the McNamara and Mount Isa groups of the Western Subprovince of the inlier. Recognition of felsic and mafic intrusions with ca 1640 Ma and ca 1615 Ma ages. Evidence for Riversleigh Inversion event ca 1640 in the Eastern Subprovince.