| Summary: | The eastern and south-eastern Australian passive continental margins host a series of Cenozoic basins preserved in onshore and offshore Victoria, Tasmania and South Australia. Deposition in these basins was concurrent with the Cenozoic Magmatic Province that extends along the Australian eastern and south-eastern Australian passive continental margin. Although classified as a ‘non-volcanic’ passive margin, a large record of igneous rocks is preserved within the Cretaceous to Miocene syn- and post-rift successions of the offshore basins. Previous studies have mainly focussed on onshore magmatic activity and resulting geodynamic models have proposed on mantle plumes or edge-driven convection. Offshore 2D and 3D seismic reflection datasets in the Bass and Gippsland Basins analysed in this thesis have shown that the magmatism in these areas occurred during the Late Cretaceous, Eocene to Oligocene and Miocene to Recent times. The majority of magmatism significantly post-dates continental break-up and basin rifting related to the separation of Australia and Antarctica, which started around 85 Ma. This thesis presents major and trace element and isotope geochemistry of Cenozoic igneous rocks in onshore Tasmania and in the offshore Gippsland and Bass Basins. The data presented suggest that magmas have formed over a thermal upwelling with a long time-integrated high 238U/204Pb or μ (HIMU) signature that traversed a Pacific Mid-Ocean Ridge Basalt (MORB) -like asthenosphere and interacted with the mantle lithosphere. Tasmanian lavas formed at different depths with shallow silica-oversaturated melts undergoing larger degrees of melting than deeper silica-undersaturated melts (> 20 kbar). These shallow melts have then mixed with a remnant source of Ferrar Jurassic magma, related to Gondwana break-up, residing in the lithosphere. Magmas formed in the Gippsland and Bass Basins formed under similar conditions as the shallow silica-oversaturated melts with varying Oceanic Island Basalt (OIB) to Upper Continental Crust (UCC) ...
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