Archival and recent boreholes over an area of c. 3 km2 have revealed complex magma-host interaction at the termination of an olivine–dolerite sill in Fife. The sill interior has zones rich in plastically deformed, vesiculated heterogeneous sediment surrounded by amygdaloidal basalt. Sediments at the contacts have been reconstituted and enclose blebs of chilled vesicular basalt. Intrusion into low rank coal seams has produced multicomponent tuffisite. A vertically nested and laterally fingered sill front is envisaged as having propagated down dip under a thin cover (<500 m) of wet Namurian sediments. Non-explosive bulk interaction of fluidised sediment and devolatilising magma occurred at intrusive contacts. Steam explosivity was more vigorous where lobes of magma repeatedly intruded moist lignite, to produce compositionally banded tuffisite rich in basalt clasts and coal fragments. The hydrovolcanic explosions did not give rise to surface eruptions because the low volumes of porewater and the high permeability and low tensile strength of the lignite prevented a build-up of high pressure steam.
