Lateral magma flow in sill-complexes

The structure of magma plumbing systems controls the distribution of volcanism and influences tectonic processes. Yet determining the structure of such 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. Our current view is thus that plumbing systems are dominated by the vertical transfer of magma via dykes and/or some form transcrustal networks of conduits and reservoirs, extending from a melt source to overlying reservoirs and eruption sites. Whilst there is a wealth of evidence to support the occurrence of vertically dominated systems, field- and seismic reflection–based observations highlight that extensive lateral magma transport (over 10’s to 1000’s kilometres) may occur within mafic sill-complexes. Most mafic sill-complexes occur within sedimentary basins, but some intrude crystalline continental crust and volcanoes, and consist of interconnected sills and inclined sheets. Yet the extent to which active volcanic systems and rifted margins are underlain by sill-complexes remains poorly constrained, despite important implications to elucidating magmatic processes, melt volumes, and melt sources. Furthermore, questions remain as to how magma can travel through sill-complexes, across vast areas, without erupting or freezing. Here, we demonstrate how we can use geophysical data (particularly seismic reflection), tempered with geological structural, petrological, and chemical data, to map sill-complexes and understand their construction.