Mafic potassic lavas of the Quaternary West Eifel volcanic field

Abstract

Major and trace element analyses for 103 volcanoes of the Quaternary West Eifel volcanic field show the lavas to be dominantly primitive (MgO>7 wt.%) and potassic (Na2O/K2O∼1). The rocks are divided into (1) a foidite (F)-suite, volumetrically dominant and consisting of four types: leucitites and nephelinites, melilite-bearing foidites, olivine-free foidites, sodalite-bearing melilite-free foidites, and (2) a younger olivine-nephelinite and basanite (ONB)-suite, concentrated in the southeastern part of the field. Dominantly cpx-phyric F-suite magmas differ from the dominantly ol-phyric ONB-suite mainly in higher K2O/ Na2O and CaO/Al2O3-ratios, higher Rb, Cu, H2O, CO2 and LREE concentrations and slightly lower Sr, Ni and Y contents. Most magmas have fractionated small amounts of olivine, clinopyroxene, and minor phlogopite. Systematic compositional variations within volcanoes or volcano groups are rare. Five more differentiated volcanoes (2 tephrites, 3 phonolites) occur in the center of the field. Their magmas are interpreted to have formed by fractionation within crustal magma chambers.