Salt-magma interactions influence intrusion distribution and salt tectonics in the Santos Basin, offshore Brazil

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 38 igneous intrusions spatially related to thick Aptian salt. Based on identified seismic-stratigraphic relationships, we suggest sill emplacement likely occurred during the late Albian-to-Santonian. 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 presalt Merluza Graben, an area characterized 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 crystallization 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.

Automated summary

This study examines the interaction between evaporites and magma in sedimentary basins, focusing on how it influences salt tectonics and magma emplacement. By analyzing the seismic data from the Santos Basin, the research identifies the timing and spatial relationship of igneous intrusions with thick Aptian salt deposits. The study suggests that the interaction between salt and magma can influence salt tectonics and the distribution of magma plumbing systems, ultimately impacting basin evolution.