A Petrologic Study of the 1982 Summit Lavas of Kilauea Volcano, Hawaii

This study presents detailed petrography, mineral analyses, and wholerock major and trance element analyses of the Kilauea Volcano summit lavas erupted in April and September 1982. It supplements earlier U.S. Geological Survey wet chemical major element analyses of the rocks. The purpose of this study is to identify the petrologic process(es) responsible for chemical variations in the lavas, and compare the chemistry of the 1982 lavas to those of previous Kilauea summit eruptions. The result show that the lavas erupted in April are chemically homogeneous. Lavas from the shorter but more voluminous September eruption vary systematically during the eruption from higher to lower MgO content. Computer modeling of the geochemical data indicates that olivine with minor clinopyroxene fractionation is probably responsible for the variation in lava compositions. The nearly aphyric nature of the lavas negates the possibility of olivine accumulation to explain the variation. Magma mixing in also an unlikely mechanism because the variations are nonlinear. The lavas from the two 1982 eruptions may be related to a common parental magma, although there are some differences in Ni between the magmas. The April lavas are very similar in composition to other historic lavas erupted in the central area of Kilauea caldera. The MgO range in the lavas from the brief September eruption represents about half of the total MgO variation of lavas erupted inside the caldera during historic time (after 1790)