Geophysical and geochemical evidence for a new mafic magmatic province within the Northwest Shelf of Australia: Supplementary material

Buried magmatic provinces are rarely identified and difficult to classify. The Northwest Shelf of Australia contains large volumes of potentially interconnected mafic igneous material across several sedimentary basins. However, limited study and a lack of surface exposure have prevented detailed description and classification of these rocks. In this study, the distribution and composition of these mafic igneous rocks is described using an integrated geophysical and geochemical approach, which included over 10,000 km of 2D historical seismic data, well log data and chemical analysis of samples from 14 wells across the Browse, Roebuck, Canning and North Carnarvon basins. Using this combined dataset, we demonstrate interconnectivity of buried mafic igneous rocks across the Northwest Shelf and calculate for these mafic rocks a total surface area exceeding 280,000 km2 and a cumulative minimum volume of ~140,000 km3. Petrology and geochemistry of samples indicate they are basaltic and doleritic with alkaline and sub-alkaline compositions and formed in a continental rift setting. Collectively, the igneous rocks meet the criteria for classification as a mafic magmatic province (MMP) and closely match the criteria required for classification as a large igneous province (LIP). The interconnected mafic igneous rocks found across the Northwest Shelf of Australia are here formally defined as an MMP. Emplacement of the Northwest Shelf MMP may represent hotspot magmatism that could have initiated rifting of the Cimmerian Block from NW Australia near the end Permian, and may have broad implications for petroleum prospectivity, CO2 sequestration and new resource opportunities in the Northwest Shelf