RARE-EARTH ELEMENT INVERSIONS AND PERCOLATION MODELS FOR HAWAII

A detailed study has been made of the evolution with time of the mantle source and degree of melting required to produce a typical Hawaiian volcano. The preshield stage involves a change from a depleted to a primitive mantle source and an increase in the melt fraction. Important intra- and inter-volcano variations occur during the shield stage which may be related to melt transport processes. With time, Mauna Loa's lavas show depletion in increasingly compatible elements, a result which is consistent with percolation processes. Postshield magmas are generated by very small degrees of melting of a depleted mantle source and may be important in the development of posterosional volcanism. Posterosional lavas can be generated by variable degrees of melting of an amphibole-bearing source that has been enriched by postshield magma. A simple percolation model is consistent with the isotopic evolution of Hawaiian volcanoes. All of the observed isotopic variation seen between Hawaiian volcanoes may be produced from only two mantle sources by small variations in the percolation processes.