The structure of upper crustal magma plumbing systems controls the distribution of volcanism and influences tectonic processes. However, delineating the structure and volume of plumbing systems is difficult because (1) active intrusion networks cannot be directly accessed; (2) field outcrops are commonly limited; and (3) geophysical data imaging the subsurface are restricted in areal extent and resolution. This has led to models involving the vertical transfer of magma via dikes, extending from a melt source to overlying reservoirs and eruption sites, being favored in the volcanic literature. However, while there is a wealth of evidence to support the occurrence of dike-dominated systems, we synthesize field-and seismic reflection-based observations and highlight that extensive lateral magma transport (as much as 4100 km) may occur within mafic sill complexes. Most of these mafic sill complexes occur in sedimentary basins (e.g., the Karoo Basin, South Africa), although some intrude crystalline continental crust (e.g., the Yilgarn craton, Australia), and consist of interconnected sills and inclined sheets. Sill complex emplacement is largely controlled by host-rock lithology and structure and the state of stress. We argue that plumbing systems need not be dominated by dikes and that magma can be transported within widespread sill complexes, promoting the development of volcanoes that do not overlie the melt source. However, the extent to which active volcanic systems and rifted margins are underlain by sill complexes remains poorly constrained, despite important implications for elucidating magmatic processes, melt volumes, and melt sources.

The structure of upper crustal magma plumbing systems controls the distribution of volcanism and influences tectonic processes. However, delineating the structure and volume of plumbing systems is difficult because (1) active intrusion networks cannot be directly accessed; (2) field outcrops are commonly limited; and (3) geophysical data imaging the subsurface are restricted in areal extent and resolution. This has led to models involving the vertical transfer of magma via dikes, extending from a melt source to overlying reservoirs and eruption sites, being favored in the volcanic literature. However, while there is a wealth of evidence to support the occurrence of dike-dominated systems, we synthesize field-and seismic reflection-based observations and highlight that extensive lateral magma transport (as much as 4100 km) may occur within mafic sill complexes. Most of these mafic sill complexes occur in sedimentary basins (e.g., the Karoo Basin, South Africa), although some intrude crystalline continental crust (e.g., the Yilgarn craton, Australia), and consist of interconnected sills and inclined sheets. Sill complex emplacement is largely controlled by host-rock lithology and structure and the state of stress. We argue that plumbing systems need not be dominated by dikes and that magma can be transported within widespread sill complexes, promoting the development of volcanoes that do not overlie the melt source. However, the extent to which active volcanic systems and rifted margins are underlain by sill complexes remains poorly constrained, despite important implications for elucidating magmatic processes, melt volumes, and melt sources.

Seismic reflection data allow for the 3D imaging of monogenetic edifices and their corresponding plumbing systems. This is a powerful tool in understanding how monogenetic volcanoes are fed and how pre-existing crustal structures can act as the primary influence on their spatial and temporal distribution. This study examines the structure and lithology of host-rock as an influence on edifice alignment and provides insight into the structure of shallow, sub-volcanic monogenetic plumbing systems. The anticlinal Ben Nevis Structure, located in the northerly extent of the Faroe–Shetland Basin, NE Atlantic Margin, was uplifted during the Late Cretaceous and Early Paleocene by the emplacement of a laccolith and a series of branching sills fed by a central conduit. Seismic data reveal that multiple intrusions migrated up the flanks of the Ben Nevis Structure after its formation, c. 58.4 Ma (Kettla-equivalent), and fed a series of scoria cones and submarine volcanic cones. These monogenetic edifices are distributed around the crest of the Ben Nevis Structure. The edifices are fed from a complex network of sills and transgressive sheets, involving lateral magma migration of tens of kilometres before extrusion at the surface. This work highlights the importance of underlying basin structures in influencing the sites and development of subaerial monogenetic fields, and the importance of lateral magma flow within volcanic systems. Supplementary materials: The results of the statistical alignment analysis of the monogenetic edifices are available at https://doi.org/10.6084/m9.figshare.c.3662809 .

No abstract