Petrology and new data on the geochemistry of the Andahua volcanic group (Central Andes, southern Peru)

- To review geochemical and isotopic data from all the regions containing volcanic centres of Andahua Group.
- To constrain the geochemical and isotopic compositions of their parental magmas sources.
- To compare the evolution of the magma sources through space and time.
- To compare petrological characteristic with Barroso Group also occurrence in this region.
- To study the petrogenetic model of Andahua Group volcanoes activity.

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.