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Adakite-like lavas from Antisana Volcano (Ecuador): evidence for slab melt metasomatism beneath Andean Northern Volcanic Zone

Abstract:

Extensive sampling of the Antisana volcano in Ecuador (Northern Volcanic Zone of the Andes) has revealed the presence of adakite-like rocks throughout the edifice, i.e. rocks with geochemical characteristics close, but not identical, to those of slab melts. Two main volcanic groups have been distinguished, characterized by two distinct evolutionary trends. The AND group, mostly composed of andesites, shows the clearest adakitic characteristics such as high La/Yb and Sr/Y ratios and low heavy rare earth element (HREE) contents. The CAK group, composed of high-K andesites and dacites, displays less pronounced adakitic-like characteristics. Although the more basic rocks of each group are difficult to distinguish on many geochemical diagrams, a geochemical study shows that the evolution of the AND and CAK groups is dominated by different petrogenetic processes. The isotopic characteristics of the CAK …