MELT GENERATION BY PLUMES - A STUDY OF HAWAIIAN VOLCANISM

The mantle plume underlying the Hawaiian Swell has been modelled numerically using a stationary steady axisymmetric plume under a solid conducting lid. A method of calculating the rate of melt production from the plume has been developed, and the total melt production rate, the residual depth anomaly and the geoid anomaly have been used to constrain the model. The plume has a central potential temperature of 1558-degrees-C and the mechanical boundary layer is 72 km thick. An average of 6.6% melting occurs in a melt-producing region which has a vertical extent of approximately 55 km and a radial extent of approximately 130 km to produce 0.16 km3/y of melt. A parameterization of melt composition has been developed that is consistent with laboratory experiments, with models of MORB generation, and with primitive Hawaiian tholeiites containing approximately 16% MgO. There is no evidence that the major and minor element concentrations in the source region of Hawaiian tholeiites differ from those in the source region of MORB. The model is consistent with the REE contents of Kilauean tholeiites if the source region has primitive REE contents. The viscosity of the low-viscosity layer is constrained to be approximately 10(16) m2/s.