The structure, distribution and environmental implications of voluminous sill and hydrothermal vent complexes in the Vøring and Møre basins

The magma plumbing system of large igneous provinces may include emplacement of voluminous sill complexes in sedimentary basins. Key examples include the North Atlantic Igneous Province (NAIP; c. 56 Ma), the Karoo-Ferrar province (c. 183 Ma), and the Siberian Traps province (c. 251 Ma). In these basins, thousands of kilometer-sized hydrothermal vent complexes are associated with the sill complexes. We have interpreted new and legacy 2D and 3D seismic data in the Vøring and Møre basins offshore Norway to characterize the sill and hydrothermal vent complexes in a 100,000 km² large region. The upper part of one of the hydrothermal vent complexes, the Modgunn Vent, was cored by five boreholes during IODP Expedition 396 in 2021. Saucer-shaped sills and overlying domes at the Top Paleocene level characterize the Jolnir, Tulipan and Infinity sill complexes in the Møre Basin. In contrast, sill complexes in the Vøring Basin display more variable morphologies, including ponding thick sheets and transgressive sheets reflecting the variations in deep basin structure and type of host rocks. The extensive Vivel Sill in the Vigrid Syncline is locally more than 200 m thick in the deeper parts of the basin, with some domal-shaped geometries that crosscut the deep basin stratigraphy and layer-parallel planar geometries at shallow stratigraphic levels. The hydrothermal vent complexes are mainly present as pipe-like disruptive seismic anomalies above transgressive sill segments connecting the contact aureoles with crater- or eye-shaped upper parts of the vent complexes near the Top Paleocene reflection. Scientific and industry drilling samples document that the vent craters were infilled during earliest Eocene times, most likely related to sill emplacement during the Paleocene-Eocene Thermal Maximum (PETM). In conclusion, the current geometries of voluminous igneous sheet intrusions both reflect the pre-emplacement deep basin structure and post-emplacement structural deformation, whereas the contact metamorphic processes triggers pipe-like deformation and focused fluid flow during formation of hydrothermal vent complexes.