The Iceland plume has played an influential role in the evolution of the North Atlantic Ocean and margins over the past 60 m.y. It is believed that this plume formed at the conjunction of a tetrad of hot, subvertical, convective sheets. The impingement of these hot sheets at the base of the lithospheric lid caused decompressional melting, generating substantial quantities of high-temperature magma that were injected into the cold overlying lid. Over the next 10 m.y., these sheets partly coalesced to form a crudely axisymmetric plume head. Here we analyze the lithospheric fingerprint of one of these hot convective sheets. By forward and inverse modeling of densely sampled wide-angle seismic data, in conjunction with gravity observations, we determined the three-dimensional shape of magmatic underplating trapped within the lithosphere. The injection of this melt into the lithosphere generated substantial permanent and minor transient uplift of Earth's surface. Predicted and measured amounts of consequent denudation and sedimentation agree within error. Temporal variations in the patterns of deposition and oceanic circulation adjacent to the convective sheet show its evolution through time and space. Our results suggest that this linear sheet has probably been directly and indirectly responsible for cyclical events over ∼60 m.y. These events have 0.5–1 and 4–6 m.y. periodicities, the existence of which may help to elucidate the dynamic behavior of convective sheets during and after impingement. Thus, in particular circumstances, surficial geological processes yield an indirect record of mantle convection and melt-generation processes.