Continental flood basalt eruptions have resulted in sudden and massive accumulations of basaltic lavas in excess of any contemporary volcanic processes. The largest flood basalt events mark the earliest volcanic activity of many major hot spots, which are thought to result from deep mantle plumes. The relative volumes of melt and eruption rates of flood basalts and hot spots as well as their temporal and spatial relations can be explained by a model of mantle plume initiation: Flood basalts represent plume "heads" and hot spots represent continuing magmatism associated with the remaining plume conduit or "tail." Continental rifting is not required, although it commonly follows flood basalt volcanism, and flood basalt provinces may occur as a natural consequence of the initiation of hot-spot activity in ocean basins as well as on continents.

We report new major element, trace element, isotope ratio, and geochronological data on the Galápagos Archipelago. Magmas erupted from the large western volcanos are generally moderately fractionated tholeiites of uniform composition; those erupted on other islands are compositionally diverse, ranging from tholeiites to picritic basanitoids. While these volcanos do not form a strictly linear age progressive chain, the ages of the oldest dated flows on any given volcano do form a reasonable progression from youngest in the west to oldest in the east, consistent with motion of the Nazca plate with respect to the fixed hotspot reference frame. Isotope ratios in the Galápagos display a considerable range, from values typical of mid‐ocean ridge basalt on Genovesa (87Sr/86Sr: 0.70259, ϵNd: +9.4, 206pb/204Pb: 18 44), to typical oceanic island values on Floreana (87Sr/86Sr: 0.70366, ϵNd: +5.2, 206pb/204Pb: 20.0). La/SmN ranges from 0.45 to 6.7; other incompatible element abundances and ratios show comparable ranges. Isotope and incompatible element ratios define a horseshoe pattern with the most depleted signatures in the center of the Galápagos Archipelago and the more enriched signatures on the eastern, northern, and southern periphery. These isotope and incompatible element patterns appear to reflect thermal entrainment of asthenosphere by the Galápagos plume as it experiences velocity shear in the uppermost asthenosphere. Both north‐south heterogeneity within the plume itself and regional variations in degree and depth of melting also affect magma compositions. Rare earth systematics indicate that melting beneath the Galápagos begins in the garnet peridotite stability field, except beneath the southern islands, where melting may occur entirely in the spinel peridotite stability field. The greatest degree of melting occurs beneath the central western volcanos and decreases both to the east and to the north and south. Si8.0, Fe8.0, and Na8.0 values are generally consistent with these inferences. This suggests that interaction between the plume and surrounding asthenosphere results in significant cooling of the plume. Superimposed on this thermal pattern produced by plume‐asthenosphere interaction is a tendency for melting to be less extensive and to occur at shallower depths to the south, presumably reflecting a decrease in ambient asthenospheric temperatures away from the Galápagos Spreading Center.

The Hawaiian-Emperor hotspot track has a prominent bend, which has served as the basis for the theory that the Hawaiian hotspot, fixed in the deep mantle, traced a change in plate motion. However, paleomagnetic and radiometric age data from samples recovered by ocean drilling define an age-progressive paleolatitude history, indicating that the Emperor Seamount trend was principally formed by the rapid motion (over 40 millimeters per year) of the Hawaiian hotspot plume during Late Cretaceous to early-Tertiary times (81 to 47 million years ago). Evidence for motion of the Hawaiian plume affects models of mantle convection and plate tectonics, changing our understanding of terrestrial dynamics.