Quantitative textural investigation of trachyandesites of Damavand volcano (N Iran): Insights into the magmatic processes
Résumé
Damavand volcano is a dormant stratovolcano in northern Iran in the middle of the Alborz Mountains. Investigation of the magmatic processes responsible for the eruption of the volcano and the conditions of the magma chamber is important in order to understand the volcanism of this system. Owing to their higher abundance and younger age, trachyandesitic rocks are the main components of this volcano. To get insights into the crystallization of these rocks, we carried out a quantitative and qualitative petrographic study of three main volcanic units erupted between 63 and 66.5 years ago. Crystal Size Distribution (CSD) studies can reveal details about magmatic processes. Measuring 4732 individual plagioclase crystals and conducting a CSD study, revealed a non-straight and concave-up CSD curve for nearly all of the studied volcanic units which suggests the occurrence of similar physico-chemical processes responsible for their magmatism. Plagioclase crystals occur as microlites and phenocrysts; the phenocrysts show either oscillatory zoning or sieve textures. Each segment of the CSD curves are consistent with a particular plagioclase texture in all the studied volcanic units. The presence of different plagioclase textures and the concave-up shape of the CSD curves suggests the variation of the physico-chemical conditions of the magma chamber during the magmatism of the Damavand in this time period. Mixing of magmas with different crystal populations can be an alternative for this phenomena. (C) 2016 Elsevier Ltd. All rights reserved.