We compile a new geochemical database (Icelandic Volcanic rocks Isotopic Database, IVID) which includes previously reported ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ¹⁷⁶Hf/¹⁷⁷Hf, ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁸Pb/²⁰⁴Pb, ¹⁸⁷Os/¹⁸⁸Os and ³He/⁴He data and major and trace element concentrations measured in Icelandic volcanic rocks. Isotopic compositions were evaluated, and filtered to identify the highest quality data and data most likely to represent mantle-derived compositions. The carefully filtered, comprehensive geochemical database is an important contribution to the geochemical community and can be used to put further constraints on the generation of geochemical heterogeneity in Iceland. We use the compiled database to examine the spatial distribution of geochemical components in the Icelandic mantle, and test whether melting processes control how source heterogeneity from the deep mantle is extracted on the surface. The PRIMELT software (which combines an inverse model for crystallization in the crust with a forward model of mantle melting to estimate the primary mantle-derived magma composition) is used to estimate mantle potential temperatures and melt fractions in Iceland. The results of these calculations and forward melting models demonstrate that mantle potential temperatures have a largely insignificant role and that lithospheric thickness plays a key role in generating geochemical heterogeneity in Icelandic volcanic rocks. Volcanic rocks from the off-rift volcanic zones are generally produced by lower melt fractions, consistent with preferential sampling of geochemically enriched and fertile “blobs” at lower degrees of melting, where the lithosphere is thicker; more geochemically depleted volcanic rocks from the axial rift zones, where the lithosphere is thinner, show higher degrees of melting, consistent with dilution of enriched blob melts by melts of more depleted and refractory mantle.