Integrated Petrological and Geophysical Constraints on Magma System Architecture in the Western Galápagos Archipelago: Insights From Wolf Volcano

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 19; no. 12; pp. 4722 - 4743
• Main Authors: Stock, Michael J., Bagnardi, Marco, Neave, David A., Maclennan, John, Bernard, Benjamin, Buisman, Iris, Gleeson, Matthew L. M., Geist, Dennis
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.12.2018
• Subjects: Archipelagoes; Augite; Crystallization; Deformation; Dynamics; Entrainment; Galapagos; InSAR; Lava; Magma; magma storage; Multidisciplinary research; Olivine; petrology; Plagioclase; Satellites; Thermobarometry; Volcanic eruptions; Volcano monitoring; Volcanoes
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2018GC007936

The 2015 eruption of Wolf volcano was one of the largest eruptions in the Galápagos Islands since the onset of routine satellite‐based volcano monitoring. It therefore provides an excellent opportunity to combine geophysical and petrological data, to place detailed constraints on the architecture and dynamics of subvolcanic systems in the western archipelago. We present new geodetic models that show that pre‐eruptive inflation at Wolf was caused by magma accumulation in a shallow flat‐topped reservoir at ~1.1 km, whereas edifice‐scale deformation during the eruption was related to a deflationary source at 6.1–8.8 km. Petrological observations suggest that the erupted material was derived from both a subvolcanic mush and a liquid‐rich magma body. Using a combination of olivine‐plagioclase‐augite‐melt (OPAM) and clinopyroxene‐melt barometry, we show that the majority of magma equilibration, crystallization, and mush entrainment occurred at a depth equal to or greater than the deep geodetic source, with little petrological evidence of material sourced from shallower levels. Hence, our multidisciplinary study does not support a fully transcrustal magmatic system beneath Wolf volcano before the 2015 eruption but instead indicates two discrete storage regions, with a small magma lens at shallow levels and the major zone of magma storage in the lower crust, from which most of the erupted material was sourced. A predominance of lower crustal magma storage has previously been thought typical of subvolcanic systems in the eastern Galápagos Archipelago, but our new data suggest that this may also occur beneath the more active volcanoes of the western archipelago. Key Points Combined geophysical and petrological constraints provide a detailed picture of the subvolcanic architecture at Wolf volcano Wolf is underlain by two discrete magma storage regions: one within the edifice, the other in the lower crust Almost all the magma ejected during the 2015 eruption of Wolf was derived from the lower crust