Petrology and new data on the geochemistry of the Andahua volcanic group (Central Andes,southern Peru) |
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| Institution: | 1. Department of Physical and Environmental Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ontario M1C 1A4, Canada;2. Institut für Geologie, Universität Hamburg, Bundesstrasse 5, 20146 Hamburg, Germany;1. South Andes Volcano Observatory, Geological and Mining Chilean Service, Rudecindo Ortega 03850, Temuco, Chile;2. Departamento de Ciencias Físicas, Universidad de la Frontera, casilla 54-D, Temuco, Chile |
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| Abstract: | The Quaternary Andahua volcanic group is located within the Central Volcanic Zone in Southern Peru. The author presents new data on major and trace elements and 87Sr/86Sr and 143Nd/144Nd ratios for Andahua rocks from all regions with volcanic centres. The TAS data identify the Andahua lavas as trachyandesites, basaltic trachyandesites and dacites. The phenocrysts are represented mainly by plagioclase, but olivine, clinopyroxene and hornblende are also present. In some cases the trachyandesites show Ca enrichment and their plagioclases have an andesine–bytownite composition. The plagioclase phenocrysts show a slight normal and occasionally reverse zonation. Their basaltic parental magmas were enriched in fluids derived from dehydration of the subducted oceanic crust. The chemical content of the Andahua volcanic rocks shows some similarity to both the slightly older and the contemporaneous and widespread Barroso Group rocks in this region. |
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| Keywords: | Plagioclases Phenocrysts Trachyandesite Andahua Group Peruvian Andes |
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