A thermal model for the origin of post-erosional alkalic lava, Hawaii

The model of lithospheric thinning and reheating for the origin of the Hawaiian swell assumes that the lower lithosphere (> 60 km) is rapidly reset to an asthenospheric temperature as it passes over the hot spot. It is shown that this heat input induces melting in a few kilometer thick layer of lithosphere just above the thermal anomaly. By solving the appropriate energy equation, the mean degree of melting in the molten layer was estimated to be 1-5% with a total melt thickness of 25-150 m. The minimum width of the thermal anomaly required to account for the observed rate of post-erosional eruptions is of the order of 10-40 km which is probably satisfied. The melt generated by this process matches the petrological and geochemical characteristics of Hawaiian post-erosional lava and their typical MORB-related isotopic signature. Because small degrees of melting are involved, the extraction time scale is long (a few million years) and is consistent with the time span of post-erosional eruptions. Also, the characteristic sequence of Hawaiian volcanism can be explained if the source for Hawaiian lava is considered as a molten layer with melt fraction decreasing upward.