Cratonic margins host many of the natural resources upon which our society depends. Despite this, little is known about the dynamic evolution of these regions and the stability of substantial steps in plate thickness that delineate their boundaries with adjacent mantle. Here, we investigate the spatio-temporal evolution of Australian cratonic lithosphere and underlying asthenospheric mantle by using the geochemical composition of mafic volcanic or shallow intrusive rocks preserved throughout the continent’s history. We have collated a large database of mafic samples that were screened to remove data affected by crystal fractionation or assimilation of cumulate material. We use forward and inverse modelling of igneous trace element compositions to calculate the depth and extent of melting for 28 distinct igneous provinces in the North Australian Craton. These results are used to infer mantle potential temperature and lithospheric thickness at the time of eruption. The majority of Paleoproterozoic magmatic events record high mantle potential temperatures of 1350–1450 °C and relatively low lithospheric thicknesses of ≤50 km. In contrast, younger igneous provinces show a gradual decrease in potential temperature and an increase in lithospheric thickness with time. These constraints on the mantle lay the foundation for the development of a quantitative geodynamic understanding of the evolution of the Australian lithosphere and its resources. <b>Citation:</b> Klöcking, M., Czarnota, K., Champion, D.C., Jaques, A.L. and Davies, D. R., 2020. Mapping the cover in northern Australia: towards a unified national 3D geological model. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

There is a growing recognition that lithospheric structure places first-order controls on the distribution of resources within the upper crust. While this structure is increasingly imaged using geophysical techniques, there is a paucity of geological constraints on its morphology and temporal evolution. Cenozoic intraplate volcanic rocks along Australia’s eastern seaboard provide a significant opportunity to constrain mantle conditions at the time of their emplacement and thereby benchmark geophysical constraints. This volcanic activity is subdivided into two types: age-progressive provinces generated by the passage of mantle plumes beneath the plate; and age-independent provinces, which may arise from edge-driven convection at a lithospheric step. In this study, we collected and analysed 78 igneous rock samples from both types of volcanoes across Queensland. We combined these analyses with previous studies to create and augment a comprehensive database of Australian Cenozoic volcanism. Geochemical modelling techniques were used to estimate mantle temperatures and lithospheric thicknesses beneath each province. Our results show that melting occurred at depths of 45–70 km across eastern Australia. Mantle temperatures are inferred to be ~50–100 °C higher beneath age-progressive provinces than beneath age-independent provinces. These results agree with geophysical observations used to aid resource assessments and indicate that upper mantle temperatures have varied over Cenozoic times. <b>Citation:</b> Ball, P.W., Czarnota, K., White, N.J. and Champion, D.C. 2020. Exploiting Cenozoic volcanic activity to quantify upper mantle structure beneath eastern Australia. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.