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Numerical models of groundwater flow play a critical role for water management scenarios under climate extremes. Large-scale models play a key role in determining long range flow pathways from continental interiors to the oceans, yet struggle to simulate the local flow patterns offered by small-scale models. We have developed a highly scalable numerical framework to model continental groundwater flow which capture the intricate flow pathways between deep aquifers and the near-surface. The coupled thermal-hydraulic basin structure is inferred from hydraulic head measurements, recharge estimates from geochemical proxies, and borehole temperature data using a Bayesian framework. We use it to model the deep groundwater flow beneath the Sydney–Gunnedah–Bowen Basin, part of Australia's largest aquifer system. Coastal aquifers have flow rates of up to 0.3 m/day, and a corresponding groundwater residence time of just 2,000 years. In contrast, our model predicts slow flow rates of 0.005 m/day for inland aquifers, resulting in a groundwater residence time of ∼ 400,000 years. Perturbing the model to account for a drop in borehole water levels since 2000, we find that lengthened inland flow pathways depart significantly from pre-2000 streamlines as groundwater is drawn further from recharge zones in a drying climate. Our results illustrate that progressively increasing water extraction from inland aquifers may permanently alter long-range flow pathways. Our open-source modelling approach can be extended to any basin and may help inform policies on the sustainable management of groundwater. [ABSTRACT FROM AUTHOR]

The surface heat flow field in Australia has for many years been poorly constrained compared to continental regions elsewhere. 182 recent heat flow determinations and 66 new heat production measurements for Southeastern Australia significantly increase our understanding of local and regional lithospheric thermal regimes and allow for detailed thermal modelling. The new data give a mean surface heat flow for Victoria of 71 ± 15 mW m - 2 which fits within the 61–77 mW m - 2 range reported for Phanerozoic-aged crust globally. These data reveal three new thermally and compositionally distinct heat flow sub-provinces within the previously defined Eastern Heat Flow Province: the Delamerian heat flow sub-province (average surface heat flow 60 ± 9 mW m - 2 ); the Lachlan heat flow sub-province (average surface heat flow 74 ± 13 mW m - 2 ); and the Newer Volcanics heat flow sub-province (average surface heat flow 72 ± 16 mW m - 2 ) which includes extreme values that locally exceed 100 mW m - 2 . Inversions of reduced heat flow and crustal differentiation find that the Delamerian sub-province has experienced significant crustal reworking compared to the Lachlan and Newer Volcanics sub-provinces. The latter has experienced volcanism within the last 8 Ma and the degree of variability observed in surface heat flow points (up to 8 mW m - 2 per kilometre laterally) cannot be replicated with steady-state thermal models through this sub-province. In the absence of a strong palaeoclimate signal, aquifer disturbances, or highly enriched granites, we suggest that this high variability arises from localised transient perturbations to the upper crust associated with recent intraplate volcanism. This is supported by a strong spatial correlation of high surface heat flow and known eruption points within the Newer Volcanics heat flow sub-province. [ABSTRACT FROM AUTHOR]

The eastern margin of Australia has experienced extensive mafic volcanism since its breakaway from Antarctica (~ 80 Ma). A plume origin has been suggested for intraplate volcanism, however, the timing and location of eruption points does not clearly correlate with Australia's northward motion of 5-8cm/yr. That Cenozoic volcanism coincides with dynamically supported topography of up to 1km throughout the eastern highlands suggests a complex interaction between a mantle plume and lithospheric geometry as Australia migrated northward. Further complications to the expression of volcanism and dynamic topography arise from boundary forces such as the sinking eastern Gondwana slab and large Pacific mantle upwelling. We present a synthesis of geochemistry, seismic, and geodynamic constraints within an integrated plate reconstruction of Australia over the last 80 million years. This provides a framework within which to test geodynamic models that match geophysical and geochemical observations. [ABSTRACT FROM AUTHOR]