The nature of the substrate below the northern Lachlan Orogen and the southern Thomson Orogen is poorly understood. We investigate the nature of the mid- to lower-crust using O and Lu-Hf isotopes on zircons from magmatic rocks which intrude these regions, and focus on the 440–410 Ma time window to minimise temporal effects while focussing on spatial differences. Over the entire region, O-isotope values range from δ18O = 5.52‰ to 10.14‰, and Lu-Hf from εHft = -8.1 to +8.5. In the northern Lachlan Orogen and much of the southern Thomson Orogen, magmatic rocks with low εHft (c. -8 to -4) and elevated δ18O (c. 9 to 10‰) reflect a supracrustal source. Magmatic rocks intruding the Warratta Group in the western part of the Thomson Orogen also have low εHft (c. -10 to -6) but more subdued δ18O (c. 7‰), indicating a distinct supracrustal source in this region. In the northeast Lachlan Orogen, magmatic rocks record mixing of the supracrustal source with input from a juvenile source (εHft as high as +8.5, δ18O as low as 5.52‰), most likely of “Macquarie Arc”-type affinity. Samples in the west-southwest Thomson Orogen also record some evidence of juvenile input (εHft as high as +0.2, δ18O as low as 6.51‰), likely the Mount Wright Arc of the Koonenberry Belt. Our results show that internal isotopic variation within the Lachlan and the Thomson orogens is much greater than the difference between the two orogens. <b>Citation:</b> K. Waltenberg, S. Bodorkos, R. Armstrong & B. Fu (2018) <i>Mid- to lower-crustal architecture of the northern Lachlan and southern Thomson orogens: evidence from O–Hf isotopes, </i>Australian Journal of Earth Sciences, 65:7-8, 1009-1034, DOI: 10.1080/08120099.2018.1463928

This web service provides access to the Geoscience Australia (GA) ISOTOPE database containing compiled age and isotopic data from a range of published and unpublished (GA and non-GA) sources. The web service includes point layers (WFS, WMS, WMTS) with age and isotopic attribute information from the ISOTOPE database, and raster layers (WMS, WMTS, WCS) comprising the Isotopic Atlas grids which are interpolations of the point located age and isotope data in the ISOTOPE database.

This web service provides access to the Geoscience Australia (GA) ISOTOPE database containing compiled age and isotopic data from a range of published and unpublished (GA and non-GA) sources. The web service includes point layers (WFS, WMS, WMTS) with age and isotopic attribute information from the ISOTOPE database, and raster layers (WMS, WMTS, WCS) comprising the Isotopic Atlas grids which are interpolations of the point located age and isotope data in the ISOTOPE database.

This web service provides access to the Geoscience Australia (GA) ISOTOPE database containing compiled age and isotopic data from a range of published and unpublished (GA and non-GA) sources. The web service includes point layers (WFS, WMS, WMTS) with age and isotopic attribute information from the ISOTOPE database, and raster layers (WMS, WMTS, WCS) comprising the Isotopic Atlas grids which are interpolations of the point located age and isotope data in the ISOTOPE database.

The Kalkadoon-Leichhardt Domain of the Mount Isa Inlier has been interpreted to represent the ‘basement’ of the larger inlier, onto which many of the younger, economically prospective sedimentary and volcanic units were deposited. The domain itself is dominated by 1860–1850 Ma granitic to volcanic Kalkadoon Supersuite rocks, but these units are interpreted to have been emplaced/erupted onto older units of the Kurbayia Metamorphic Complex. This study aims to provide insights into a number of geological questions: 1. What is the isotopic character of the pre-1860–1850 Ma rocks? 2. How do these vary laterally within the Kalkadoon-Leichhardt Domain? 3. What is the tectonic/stratigraphic relationship between the 1860–1850 Ma rocks of the Mount Isa Inlier and c. 1850 Ma rocks of the Tennant Creek region and Greater McArthur Basin basement? Detrital zircon U–Pb results indicate the presence of 2500 Ma detritus within the Kurbayia Metamorphic Complex, suggesting that the Kalkadoon-Leichhardt Domain was a sedimentary depocentre in the Paleoproterozoic and potentially had sources such as the Pine Creek Orogen, or, as some authors suggest, potential sources from cratons in northern North America. Existing Hf and Nd-isotopic data suggest that the ‘basement’ units of the Mount Isa Inlier have early Proterozoic model ages (TDM) of 2500–2000 Ma. Oxygen and Hf-isotopic studies on samples from this study will allow us to test these models, and provide further insights into the character and history of these ‘basement’ rocks within the Mount Isa Inlier, and northern Australia more broadly.