Petrogenesis of a highly contaminated magmas by ascent through a thick continental crust: The case of Sairecabur volcano, Central Andes.2025. Loaiza. C; Godoy B; Freire. N; González-Maurel.O; Rodríguez Araneda. I;Petrus le Roux; Figueroa. J.

Magmas in the Central Andes have evolved through fractional crystallization and crustal assimilation, operating at different crustal levels during their ascent through the ∼70 km-thick continental crust. Sairecabur stratovolcano, located within the Altiplano–Puna Volcanic Complex (APVC; 21°–24° S) of the Central Andean subduction zone, is stratigraphically divided into three units: Pre-Caldera Lavas (PRECL – Pleistocene), Post-Caldera I Lavas (POCIL – Upper Pleistocene), and Post-Caldera II Lavas (POCIIL – Holocene). These volcanic products range from 55 (basaltic andesite) to 63 (dacite) wt.% SiO₂. In particular, Sairecabur shows a negative correlation between SiO₂ wt.% and Eu/Eu∗, with Eu/Eu∗ values < 1, indicating the key role of plagioclase during late-stage magma differentiation. A deep-crustal garnet signature – though not prominent – cannot be excluded, which was overprinted by shallow differentiation and assimilation. Over the past 10 Ma, APVC magmas have been affected by significant crustal contamination, linked to crustal thickening during the Andean orogeny and localized processes. This trend is observed in all units of Sairecabur, where ⁸⁷Sr/⁸⁶Sr ratios of erupted products range from 0.707057 to 0.708667. This suggests a substantial crustal assimilation of a parental Andean-type magmas (⁸⁷Sr/⁸⁶Sr ratio ∼0.705), which was generated by an early stage of magmatic differentiation at lower crustal levels (MASH zone). Petrographic and geochemical data define three main mid-to-upper crustal evolutionary stages occurring afterwards: (1) an AFC stage in mid-to upper-crustal chambers, with 33–47 % AFC-type incorporation of felsic upper crustal material; (2) an intermediate stage of closed-system fractional crystallization involving plagioclase, pyroxene, amphibole, and biotite; and (3) a late-stage episode of magma mixing with shallow crustal melts, evidenced by glomeroporphyritic gabbroic aggregates and by trace-element trends and scatter accompanying advanced differentiation.