Abstract

The evolution of the magma plumbing system of the Pleistocene Apacheta-Aguilucho Volcanic Complex area (Altiplano-Puna Volcanic Complex, northern Chile) was investigated through petrographic, geochemical and isotopic studies of representative lavas and related enclaves. Updated available dates of these products, both from the Apacheta and Aguilucho stratovolcanoes and nearby domes, allow us to define the activity during the last 1 Ma. This investigation shows that the andesitic magmas were affected by processes of Assimilation plus Fractional Crystallization (AFC, with a significant role played by amphibole fractionation) during their ascent through the upper crust, presumably by the interaction with the Altiplano-Puna Magma Body (15-20 km). These andesitic magmas were erupted with no or minor additional contamination at shallower levels, or experienced plagioclase-dominated Fractional Crystallization (FC) to dacite within shallower crustal magma chambers (4-8 km depth). The constructional phase of the Apacheta and Aguilucho stratovolcanoes (>= 1 to ca. 0.6 Ma) reflect a transition from high-flux (i.e. flare-ups) to steady state magmatism, as also documented in other Pleistocene volcanic complexes of the Altiplano-Puna Volcanic Complex. During this stage the mafic magma recharge was high enough to permit a large spectrum of hybridization of the resident magmas in the upper crust to form the abundant andesites and dacites lavas. In contrast, at similar to 150-100 ka, the magmatism turned to a new stage of recharge (waning stage?) and the episodic intrusion of small-volumes of andesitic magmas permitted the remobilization of the crystal-rich dacites, triggering the extrusions of the Chanka, Chac-Inca and Cerro Pabellon domes. The andesitic enclaves in the domes studied here represent a snapshot of the magmatic processes of interaction that occurred in the shallower reservoir at the interface of the resident dacite with the ascending andesitic magma. Nevertheless, as there are no dated volcanic products from the area between 0.6 and 0.1 Ma, the youngest dacitic domes could also be interpreted as the beginning of a new magmatic pulse of the Altiplano-Puna Volcanic Complex. Independently from the significance of the mafic recharge at 150-100 ka (waning stage vs. new pulse) the youngest investigated domes share similar geochemical features and crustal depth constraints (4-8 km) with the ignimbrites of the Altiplano-Puna Volcanic Complex, therefore suggesting that the remobilized magmas erupted as the domes are possibly remains of older plumbing systems left over from the last magmatic flare-up of the Altiplano-Puna Volcanic Complex. (C) 2019 Elsevier B.V. All rights reserved.