Geophysical and Geochemical Evidence for a New Mafic Magmatic Province Within the Northwest Shelf of Australia.

The formation of mafic magmatic provinces are significant geological events that can drive mass extinctions and continental rifting and can influence basin evolution, petroleum prospectivity and mineralization. Buried magmatic provinces, however, are rarely identified and difficult to define. 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 are described using an integrated geophysical and geochemical approach, which included over 10,000 km line length of 2D 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 data set, we demonstrate interconnectivity of buried mafic igneous rocks across the Northwest Shelf and calculate 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). Emplacement of the newly defined Northwest Shelf MMP may represent hotspot magmatism that could have initiated rifting of the Cimmerian Block from NW Australia during the Permian and could have potential for future, large scale CO2 sequestration and storage. Plain Language Summary: Magmatic provinces are large bodies of igneous rock often tied to significant changes in Earth's history such as mass extinction events and continental rifting. Many magmatic provinces are exposed on the surface and can be studied directly; however, studying magmatic provinces that are buried under hundreds to thousands of meters of sedimentary rock becomes increasingly difficult. In this paper, we indirectly map and characterize igneous rocks buried within the Northwest Shelf of Australia using seismic data and drilled rock samples. Combining these results, we found the igneous rocks all formed together, most likely during supercontinent break‐up around 250 million years ago. We conclude that these rocks represent a new magmatic province, named the Northwest Shelf Mafic Magmatic Province. Recognition of this magmatic province is exciting because it may have contributed to an important global extinction event, presents new mineral resource opportunities and may be suitable for large scale CO2 sequestration to combat climate change. Key Points: We classify a new mafic magmatic province buried beneath the Northwest Shelf of AustraliaClassification was achieved by implementing a 3D seismic stratigraphic model and integrating geophysical and geochemical findingsImplications include new resource opportunities, potential contributions to end Permian mass extinction and large scale CO2 sequestration [ABSTRACT FROM AUTHOR]