Intrusions Beneath Large Intraplate Volcanoes

Large, intraplate, mafic volcanoes, when dissected by erosion, are found to overlie a cogenetic intrusive complex. The intrusive complex causes a positive gravity anomaly, a magnetic anomaly with a positive about 10 km across and a net uplift of the country rock. The intrusive complex’s mean density is about 3.0 t m-3, with a volume about one-third the volume of volcanic rocks. For volcanoes in stable intraplate regions the space for the underlying crustal intrusive complex is likely to be created solely by uplift of the country rock above it and to the side.