The geochemistry of Icelandic volcanics, especially as pertains LIL-elements, RE-elements, and isotopes, has in the literature called for explanations involving heterogeneous mantle source. These explanations are shown to be incompatible with the data at hand. A different model, involving crustal metasomatism, is introduced and discussed, in which the observed chemical variability turns out to be a necessary consequence of the process of crustal accretion and of the geodynamics of Iceland. Crustal accretion is confined to volcanic systems that form an array of dike swarms over the plate boundary. Each system evolves independently, through cyclic processes, toward a silicic central volcano with associated extensive hydrothermal alteration, but the overall result of the accretion process is chemically, mineralogically, and seismically layered oceanic crust, capable of yielding different anatectic melts. These melts are the “metasomatic ichors” that primarily cause the variability of Icelandic volcanics. At the surface they are observed as volcanic formations, as discrete components in mixed magmas, and as chemical imprints that have been mistaken for signs of a mantle heterogeneity or mantle metasomatism.