MINERAL CHEMISTRY OF THE LLAIMA PUMICE, SOUTHERN CHILE: EVIDENCE FOR MAGMA MIXING
Unité de Recherche Argiles et Paléoclimats, Département de Géologie, Université de Liège. E-mail: fdevleeschouwer@ulg.ac.be
Laboratoire de Géographie Physique et Quaternaire, Département de Géographie, Université de Liège.
Unité de Recherche Argiles et Paléoclimats, Département de Géologie, Université de Liège.
Servicio Nacional de Geologia y Mineria, Santiago de Chile, Chili.
Abstract
This paper details the mineralogy and the chemistry of the Llaima pumice deposit from in southern Chile. This andesitic to dacitic pumice was erupted from Llaima Volcano. This eruption took place in the early Holocene through at least two pulses that are well recorded in deposits around the Icalma-Galletué area. In 2001, the Llaima pumice was sampled from six outcrops. The mineralogy has been studied under polarizing microscope and electron microprobe (EPMA). The Llaima pumice contains phenocrystals of orthopyroxene, clinopyroxene, olivine and titano–magnetite. The olivine is characterized by two chemically distinguishable populations (i.e. Fo32 to Fo35 and Fo76 to Fo82). The respective chemical compositions of these two distinct olivines emphazise that the eruption was triggered by magma mixing.