Andean volcanism: Nevado Hualca Hualca Volcano, southern Peru, and El Reventador Volcano, Ecuador
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The Hualca Hualca-Ampato-Sabancaya (HHAS) stratovolcanic complex and the adjacent Andahua Group scoria cone fields are genetically related. 143Nd/144Nd and 87Sr/86Sr isotopic data indicate that both the Andahua and HHAS complex magmas are generated from the same source and evolve via fractional crystallization and assimilation of radiogenic crust. Contamination of the magmas with 3-19% Charcani gneiss (local basement) can produce the isotopic signatures of the most radiogenic samples. A prominent gap in 87Sr/86Sr values is consistent with two separate storage regions for the Andahua Group defined by differing amounts of crustal assimilation, residence time, and likely depths of assimilation within the crust. HHAS complex magmas differentiate from the more radiogenic magmas of the Andahua Group and are periodically recharged by their mafic parents. Mafic inclusions present in the HHAS rocks are generated by dispersal of a mafic foam interface layer with the overlying silicic magma at the bases of magma chambers.