Magnesian andesites from White Island, New Zealand : Mineralogical evidence for mixing of high-magnesian basalt and dacite magmas : Mineralogical evidence for mixing of high -magnesian basalt and dacite magmas(MEMORIAL VOLUME TO THE LATE PROFESSOR TERUHIKO SAMESHIMA)

Andesiteblocks erupted from WhiteIsland voIcanoin1977 are chemically Similar to the clinopyroxene-rich magnesian andesites from the Setouchi voIcanic beltin SOuthwestJapan・However,there are differencesinmineralogy with Mg# decreasing fromolivine to clinopyroxene and orthopyroxene with a marked compositionalgap.The WhiteIsland magnesian andesite contains olivine phenocrysts normally zoned from Fo92 to Fo88,SuggeStlng that theyhave crystallized from a highmagnesian magma.In contrast,theclino-andorthopyroxenesareratherlowinMg#,Witha highest value of83.9, andmanyarereverselyzoned・TheclinopyroxenecoreswithMg#rangingfrom79to75 indicatetheir derivationfroma.magmaslgnificantlyhigherinFeO/MgOthanthehost rock・TheWhiteIsland magneslan andesites are considered to have formed bymiXlng Of ahigh,MgbasaltmagmaandadacitemagmawithrelativelyhighFeO/MgO.