Understanding how Large Igneous Provinces (LIPs) formed in the Proterozoic is subject to several challenges, including incomplete geological exposure, deformations from subsequent reworking and the lack of strong geophysical signals from the associated thermal perturbations. Here we apply a seismically-constrained gravity inversion method to the Warakurna LIP region in central-western Australia, focusing on imaging the deep crust of this region, and defining the extent and intensity of mafic magmatism. In particular a thick mafic underplate has been imaged in some continent-scale studies, but its regional extent is not well defined. The results of 3D gravity inversions demonstrate an extensive area with very thick crust (> 45 km) composed of high-density materials (> 2830 kg/m3), which is interpreted to represent a mafic underplate. Variations in mass-excess (i.e. underplate thickness and/or density) suggest that the intensity of mafic magmatism closely followed the likely lithospheric architecture of the Australian continent at the time of emplacement, with magmatic centres concentrated adjacent to craton margins and along translithospheric shear zones. This suggests that melting was focused in the Proterozoic regions with thinner lithosphere, or that upwelling mantle has been diverted into this region by the roots of the Archean cratons, or both. The mass-excess is greatest beneath the magmatic centre of the LIP in the west Musgrave Province (WMP). This arrangement is reflected in Ni-Cu-PGE prospectivity, with known deposits focused in the WMP, which has a thick, dense underplate. In contrast the Capricorn Orogen and Yilgarn Craton, which are not underplated, do not possess known deposits, despite extensive sills in the upper crust. Our results show that this method for mapping the extent and mass-excess of lower-crustal magmatic products provides an effective indicator of the extent and intensity of magmatism during LIP events, and that this can help understand LIP processes, including ore-deposit formation.