Multiple melt bodies fed the AD 2011 eruption of Puyehue-Cordón Caulle, Chile

At 18.45 UTC on June 4th, 2011, an explosive eruption (VEI ≤ 5) of rhyolitic magma1,2,3 began at Puyehue-Cordon Caulle volcanic complex (PCCVC), southern Chile and close to the frontier with Argentina. This PCC eruption was the first within this dominantly dacitic to rhyolitic fissure zone since 19604,5,6,7 (Fig. 1) and was preceded (commencing April 27th, 2011) by intensifying seismic swarms located between 2.5 and 5 km depth1. The eruption commenced with the development of a sustained Plinian eruption column that ascended to >15 km above the newly formed vent. Ash from this column circum-navigated the southern Hemisphere in less than 14 days and severely disrupted aviation in Argentina, Uruguay, South Africa, Australia, New Zealand and finally in Chile itself. By January 2012, explosive activity had declined from sustained Plinian to intermittent sub-Plinian fountaining, to mixed gas- and ash-jetting punctuated by Vulcanian blasts. This explosive activity was accompanied by synchronous effusion of obsidian lava in a hybrid explosive-effusive eruption1,3. Throughout the PCC eruption two closely spaced (<200 m), and sometimes partly overlapping, explosive loci (NW and SE vents) were noted3. The regular occurrence of synchronous blasts from both vents suggested an advanced degree of connectivity in the shallow subsurface. Figure 1 Map of the southeast portion of the PCC volcanic complex showing the location and spatial arrangement of 1921 (coloured orange), 1960 (coloured red) and 2011 (coloured yellow) fissure vents and resultant lava products (inset modified from ref. 5). Surveyed ... The position of the 2011 PCC vent(s) coincides with the intersection of the N-S oriented Liquine-Ofqui Fault zone with the 15-km long by 4 km wide NW-SE oriented Cordon Caulle fault-bounded graben with associated fissure vents, aligned domes and pyroclastic cones (Fig. 1). In this study, we determine the major- and trace-element chemistries of fresh vesicular glass shards using grain-discrete electron microprobe (EMP) and laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) techniques, respectively. Daily ash-fall samples were collected from downwind localities (SI Table 1) from the commencement of the PCC eruption on June 4th, 2011 in order to quantify any compositional evolution of the rhyolitic magma as the eruption progressed. Fresh vesicular glass was specifically selected during analysis to minimize potential contamination by conduit and/or overburden glassy materials that may have been incorporated during magma ascent.