Petrology Lunch - Fractional crystallisation of eclogite during the birth of a Hawaiian Volcano - Laura Miller

This weeks petrology lunch we will speaking on the subject of "Fractional crystallisation of eclogite during the birth of a Hawaiian Volcano" with guest speaker Laura Miller from Monash University.

 

ABSTRACT: The initial melts erupted by a Hawaiian volcano have a range of alkalic compositions but are rarely observed as they are covered by enormous volumes of shield stage tholeiites. A remarkable record of the early evolution of Hawaiian volcanoes, however, is preserved by a volcanic sandstone dredged from the submarine flank of Kilauea that contains a suite of petrogenetically related pre-shield basanite to nephelinite glasses. Here we show that the systematic variation in the rare earth element (REE) patterns of these samples requires the fractional crystallisation of garnet. A fractionating assemblage of Ca-rich garnet (32%), omphacitic clinopyroxene (63%), and minor phlogopite can explain the variation in the major and trace element contents of the suite. The results suggest fractional crystallisation of eclogite from a primitive Hawaiian melt near the base of the lithosphere (>90km) and that a deep magma chamber is the first stage in the development of a Hawaiian volcano.