Abstract

The Altiplano-Puna Volcanic Complex is a province of the Central Andes mainly associated, since the Miocene (26 Ma), with the eruption of voluminous silicic magmas (> 65 wt % SiO2). The result of these eruptions is an extensive ignimbritic plateau which covers an area > 50,000 km(2). Major eruptions (i.e. flare-up events) of these magmas occurred with a cyclic periodicity, on which each cycle last 2-3 Ma, and steady-state and/or waning periods occurred between each cycle. After the last flare-up cycle of evolution of the Altiplano-Puna Volcanic Complex (ended at ca.1 Ma), low to intermediate silica (< 59 wt % SiO2; commonly referred as "mafic") extrusive products have erupted in a scattered way throughout the magmatic province. This mafic volcanism is exposed mainly as monogenetic centers (scoria cones or maar-like structures), isolated flows, or as part of more differentiated stratovolcano complexes (e.g., San Pedro, Sairecabur, Licancabur, and Lascar). The origin of these mafic products has been related to partial melting of the mantle wedge and an evolution affected by the presence of different MASH-type zones at lower (> 40 km depth) and upper (< 40 km depth) crustal levels, with limited low-pressure fractional crystallization. Nevertheless, dacitic magma chambers (4-8 km depth) may have benefited from mafic magma inputs to be remobilized and erupted as silicic domes < 0.2 Ma (e.g. Chao Dacite). In fact, widespread enclaves hosted in these young domes represent a snapshot of the pre-eruptive magma mingling-mixing processes at the dacite-mafic interface. We are going to deal with the mafic magmas erupted after the last major flare-up ignimbritic phase-i.e. during the last 1 Ma-when the Altiplano-Puna Volcanic Complex entered in a steady-state stage. Such mafic products, mainly erupted near the border or outside of the well detected Altiplano-Puna Magma Body located in the upper crust, can help to unravel the evolution of the present-day Arc Magmatic Stage of this large volcanic silicic province.