Craig Magee , Leonardo Muniz Pichel, Amber Madden-Nadeau, Christopher Aiden-Lee Jackson , Webster Mohriak

Many sedimentary basins host thick evaporite (salt) deposits. Some of these basins also host extensive igneous intrusion networks. It thus seems inevitable that, in some locations, magma will interact with salt. Yet how interaction between these materials may influence salt tectonics or magma emplacement, particularly at the basin-scale, remains poorly understood. We use 3D seismic reflection data from the Santos Basin, offshore Brazil to image igneous intrusions spatially related to thick Aptian salt. We show intra-salt sills are geometrically similar to but laterally offset from supra-salt sills. We suggest ascending magma was arrested by the salt in some areas, but not others, perhaps due to differences in evaporite lithology. Our mapping also reveals most sills occur within and above the pre-salt Merluza Graben, an area characterised by Albian-to-Neogene, salt-detached extension. In adjacent areas, where there are few intrusions, salt deformation was driven by post-Santonian diapir rise. We suggest emplacement of hot magma within evaporites above the Merluza Graben enhanced Albian-to-Santonian salt movement, but that crystallisation of the intrusion network restricted post-Santonian diapirism. Our work indicates salt-magma interaction can influence salt tectonics, as well as the distribution of magma plumbing systems, and thus could impact basin evolution.