Magmatic differentiation at La Poruna scoria cone, Central Andes, northern Chile: Evidence for assimilation during turbulent ascent processes, and genetic links with mafic eruptions at adjacent San Pedro volcano

La Poruna (21 degrees 53'S; 68 degrees 30'W) is a 140 m high scoria cone composed of pyroclastic material and an extensive basaltic-andesite to andesite lava flow that is up to 8 km in length. Automated mineralogical analysis describes a suite of porphyritic mafic samples, comprising olivine- and pyroxene-bearing rocks. Well-defined major element compositional trends, as well as trace and rare earth element characteristics (e.g. Sr/Y 96 ka) from San Pedro volcano exhibit similar isotopic characteristics, therefore evidence of similar magmatic processes. This new dataset clearly defines magma compositional changes during the La Poruna eruption (ca. 100 ka), revealing an increase in crustal contamination at shallow crustal levels for the younger San Pedro lavas (<96 ka), likely controlled by increasing amounts of deep-sourced basaltic input over time. (C) 2019 Elsevier B.V. All rights reserved

The upper crustal magma plumbing system of the Pleistocene Apacheta-Aguilucho Volcanic Complex area (Altiplano-Puna, northern Chile) as inferred from the erupted lavas and their enclaves

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

Sunda arc mantle source delta O-18 value revealed by intracrystal isotope analysis

Magma plumbing systems underlying subduction zone volcanoes extend from the mantle through the overlying crust and facilitate protracted fractional crystallisation, assimilation, and mixing, which frequently obscures a clear view of mantle source compositions. In order to see through this crustal noise, we present intracrystal Secondary Ion Mass Spectrometry (SIMS) delta O-18 values in clinopyroxene from Merapi, Kelut, Batur, and Agung volcanoes in the Sunda arc, Indonesia, under which the thickness of the crust decreases from ca. 30km at Merapi to &lt;= 20km at Agung. Here we show that mean clinopyroxene delta O-18 values decrease concomitantly with crustal thickness and that lavas from Agung possess mantle-like He-Sr-Nd-Pb isotope ratios and clinopyroxene mean equilibrium melt delta O-18 values of 5.7 (+/- 0.2 1SD) indistinguishable from the delta O-18 range for Mid Ocean Ridge Basalt (MORB). The oxygen isotope composition of the mantle underlying the East Sunda Arc is therefore largely unaffected by subduction-driven metasomatism and may thus represent a sediment-poor arc end-member. Subduction zone volcanoes are underlain by extensive magma plumbing systems, which can obscure original mantle source signals. Here, the authors show that intra-crystal oxygen isotope analysis of clinopyroxenes from the Sunda arc (Indonesia) reveal the delta 18 O value of the sub-arc mantle