Origin of Holocene trachyte lavas of the Quetrupillán volcanic complex, Chile: Examples of residual melts in a rejuvenated crystalline mush reservoir Raimundo Brahm a,e, ⁎, Miguel Angel Parada a,e , Eduardo Morgado a,b,e , Claudio Contreras a,c,e , Lucy Emma McGee a,d,e a Department of Geology, Universidad de Chile, Santiago, Chile b Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK c School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK d Department of Earth and Planetary Sciences, Macquarie University, Sydney, Australia e Centro de Excelencia en Geotermia de los Andes (CEGA), Santiago, Chile abstract article info Article history: Received 11 December 2017 Received in revised form 2 April 2018 Accepted 24 April 2018 Available online 30 April 2018 The Quetrupillán Volcanic Complex (QVC) is a stratovolcano placed in the center of a NW-SE volcanic chain, be- tween Villarrica volcano and Lanín volcano, in the Central Southern Volcanic Zone of the Andes. Its youngest ef- fusive products are dominated by crystal-poor (most samples with b9 vol% phenocrysts), crystal clot-bearing trachytes (from 64.6 up to 66.2 wt% SiO 2 ), whereas the oldest units are mainly basaltic andesites. Two-stage gen- eration of QVC trachytes by differentiation at shallow depth (b1 kbar) and NNO-QFM oxidation conditions were obtained from initial melt compositions equivalent to the Huililco basalts, a small eruptive centre located ca. 12 km NE of the QVC main vent. Pyroxene-bearing crystal clots, locally abundant in the trachytes, were formed at 900–960 °C (±55 °C) and represent a dismembered crystal mush from which interstitial trachytic melts were extracted and transported upward before eruption. Heating of the crystal mush by a hotter magma recharge is inferred from complex zoned plagioclases formed at higher crystallization temperatures (50–90 °C) than those obtained from pyroxene. Ca-rich plagioclase overgrowths around more albitic cores, followed by an external rim of similar composition to the core are interpreted as restoration to the initial conditions of plagioclase crystalli- zation after the mentioned heating event. Additionally, a late heating of up to 150 °C just prior to eruption is re- corded by Fe-Ti oxide thermometry. © 2018 Elsevier B.V. All rights reserved. Keywords: Quetrupillán Trachyte Crystal clots Crystal mush Magma recharge Mush remobilization 1. Introduction At shallow levels of the crust, magma is commonly stored as highly crystalline (N50 vol% crystals) mushy chambers, where melt extraction from the crystal network is allowed by the hampering of convection, in- ducing the accumulation in the upper parts of the chamber of more dif- ferentiated crystal-poor eruptible magma (Bachmann and Bergantz, 2004; Hildreth, 2004). The survival of highly crystalline silicic reservoirs in the crust is aided by the thermal isolation effect of the crystal network (Ellis et al., 2014) and the relevant amount of latent heat released during crystallization, giving rise to a somewhat steady state in the magma evolution (Huber et al., 2009). In fact, the highly crystalline magmatic chambers can behave like rheological barriers to the intrusion of a new magma batch (Kent et al., 2010), inhibiting mixing and forcing this batch to stall beneath the bottom of the chamber, unless the intru- sion rate is high enough, to produce mush rejuvenation and magma re- mobilization by dikes (Wright et al., 2011). The remobilization of the trapped melts often produces the crystal clots and antecrysts to be dragged upward from the mush and transported to the melt accumula- tion zone (Huber et al., 2011). These crystal phases could record magma recharge processes such as thermal and compositional mixing by changes in their chemical composition and evidences of disequilibrium textures (Davidson et al., 2007; Millet et al., 2014). For example, zoning patterns in plagioclase are widely used to track changes in magma con- ditions (Berlo et al., 2007; Cashman and Blundy, 2013; Streck et al., 2008; among others) because they are commonly present during the whole differentiation process, have slow diffusion rate of mayor ele- ments (Grove et al., 1984; Liu and Yund, 1992) and record composi- tional changes that depends on of multiple variables (e.g. melt composition, temperature, pressure and H2O content; Lange et al., 2009; Almeev et al., 2012; Waters and Lange, 2015). We studied Journal of Volcanology and Geothermal Research 357 (2018) 163–176 ⁎ Corresponding author at: Institute of Agriculture and Environment, Massey University, Palmerston North 4442, New Zealand. E-mail addresses: r.brahm@massey.ac.nz (R. Brahm), maparada@cec.uchile.cl (M.A. Parada), eeeem@leeds.ac.uk (E. Morgado), cc16709@bristol.ac.uk (C. Contreras), lucy.mcgee@mq.edu.au (L.E. McGee). https://doi.org/10.1016/j.jvolgeores.2018.04.020 0377-0273/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores