Mafic intrusions, hydrothermal venting, and the basalt-sediment transition: Linking onshore and offshore examples from the North Atlantic igneous province

Abstract

The emplacement of large intrusive complexes into sedimentary basins can have profound effects on host sedimentary rocks including deformation, thermal aureole metamorphic reactions, alteration of fluid-flow pathways, and the formation of associated hydrothermal vent complexes (HVCs). These processes can in turn have major implications for petroleum systems on the local and regional scale, and can contribute to global climate change due to the production and outgassing of greenhouse gases, such as CH 4 and CO 2 . Imaging these features and assessing their implications from seismic data beneath extrusive volcanic cover is challenging due to heterogeneities in the volcanic pile and at the basalt-sediment transition. We have evaluated combined field and laboratory petrophysical data from the Isle of Skye, Scotland, where we identify a seismic-scale example of extensive intrusions interacting with the base-basalt transition. We have also evaluated a unique onshore example of a linked sill and associated HVC cutting up through the lava sequence. We compare these field results with HVCs from reflection seismic data across the Vøring Marginal High, offshore Norway, where subbasalt saucer-shaped intrusions are also seen associated with HVCs cutting the lava sequence. Seismic imaging problems associated with the velocity heterogeneity of volcanic sequences, along with a historical lack of highquality 3D data in volcanic regions worldwide, is suggested as having largely precluded the identification of these features in the past. The under-representation of these hydrothermal vents in the literature has key implications for the future appraisal of intrusion-related outgassing effects on the global climate such as those related to the Palaeocene Eocene Thermal Maximum, along with subbasalt petroleum prospectivity where they may alter maturation and migration pathways.

Segment tip geometry of sheet intrusions, II: Field observations of tip geometries and a model for evolving emplacement mechanisms

“…3a). At the level of exposure, the sills occupy ~50% of the total rock volume [Angkasa et al, 2017].…”

Breakup volcanism and plate tectonics in the NW Atlantic

“…The sills and associated vent complexes extent and volume are poorly constrained due to the limited imaging beneath sills/volcanics, and to the difficulty in measuring sill thickness from seismic data (e.g., Angkasa et al, 2017). Sub-sill imaging remains difficult partly due to transmission loss across high-impedance contrast boundaries.…”

The 3D facies architecture and petrophysical properties of hyaloclastite delta deposits: An integrated photogrammetry and petrophysical study from southern Iceland

“…Such sequences reflect eruption of lava into water bodies of various depth (often 10s to 100s of meters), which provides valuable information about the palaeo‐environments present during the onset and duration of volcanism (e.g. Angkasa et al, ; Jerram, Svensen, et al, ; Jerram, Widdowson, et al, ; Millett, Hole, Jolley, Schofield, & Campbell, ; Skilling, ; Wright et al, ). The presence of such systems introduce a potential impact on how we interpret and understand the evolution of volcanic margins and associated flood basalt sequences (Abdelmalak et al, ; Planke et al, ).…”