The petrologic evolution and pre-eruptive conditions of the rhyolitic Kos Plateau Tuff (Aegean arc)

Abstract

Abstract:The Kos Plateau Tuff is a large (>60 km 3 ) and young (160 k.y.) calc-alkaline, high-SiO 2 rhyolitic ignimbrite from the active Kos-Nisyros volcanic center in the Aegean arc (Greece). Combined textural, petrological and geochemical information suggest that (1) the system evolved dominantly by crystal fractionation from (mostly unerupted) more mafic parents, (2) the magma chamber grew over 250 000 years at shallow depth (∼1.5-2.5 kb) and was stored as a H 2 O-rich crystalline mush close to its solidus (∼670-750°C), (3) the eruption occurred after a reheating event triggered by the intrusion of hydrous mafic magma at the base of the rhyolitic mush. Rare banded pumices indicate that the mafic magma only mingled with a trivial portion of resident crystal-rich rhyolite; most of the mush was remobilized following partial melting of quartz and feldspars induced by advection of heat and volatiles from the underplated, hotter mafic influx.

Permeability measurements of Campi Flegrei pyroclastic products: An example from the Campanian Ignimbrite and Monte Nuovo eruptions

“…5). In fact, although at the same water content the melt viscosity of KPT rhyolites is higher than that of MTN and CI trachytic melts, comparable values of calculated viscosity (logη (Pa s) ≃ 4 +/− 1; as these are calculations and not measurements they have an uncertainty of the order of 1 log unit) are obtained by assuming a dissolved water content of 7 wt.% for the KPT magma (Bachmann, 2010) (logη (Pa s) ≃ 5), 3 wt.% for the MTN magma (Piochi et al, 2008) (logη (Pa s) ≃ 5), 4 wt.% for the CI magma (Piochi et al, 2008) (logη (Pa s) ≃ 3.5), and very low water content for the Ambrym magma (Allard et al, 2009) (logη (Pa s) ≃ 3). In this view, we suggest that the high permeabilities of the MTN samples could be generated by a combination of high magnetite microlite content (Fig.…”

Calderas and magma reservoirs

“…et al, 2012). By analogy with the larger systems, it is commonly assumed that evolved crystal-poor (CP) magma is segregated into a single large body prior to eruption, and that late-erupted crystal-rich (CR) magma is mobilized by recharge melts (e.g., Bacon and Druitt, 1988;Pallister et al, 1992;Allen, 2001;Bachmann, 2010). When crystal-rich magmas are erupted early (for example, Pinatubo 1991, Philippines; Quilotoa 800 ybp, Ecuador), erupted magmas appear similar to larger MI eruptions in their (general) homogeneity, bulk composition and high crystallinity (e.g., Polacci et al, 2001;Rosi et al, 2004).…”

“…2; e.g., Hildreth, 2004;Hildreth and Wilson, 2007;Lipman, 2007;Bachmann and Bergantz, 2008;Reid, 2008;Bachmann, 2010;Deering et al, 2011;Walker et al, 2013;Simon et al, 2014), (2) large melt volumes may be assembled rapidly (Charlier et al, 2005;Wilson and Charlier, 2009;Druitt et al, 2012;Allan et al, 2013;Gebauer et al, 2014;Simon et al, 2014;Wotzlaw et al, 2014), (3) caldera-forming Crystal-poor (CR), and often zoned, eruptions are fed from a single melt body contained within a much larger and more crystalline system comprising a crystal mush (~50% crystals) and surrounding rigid sponge (N65% crystals); modified from Hildreth (2004). (B) Crystalrich (CR) eruptions occur by rejuvenation of a near-rigid crystal mush (by input of melt and/or gas); modified from Bachmann and Bergantz (2006); Huber et al (2011). eruptions may be triggered either internally ('chamber triggered') or externally ('roof triggered') depending on the tectonic setting, accumulated magma volume and roof aspect ratio (Lindsay et al, 2001;Jellinek and DePaolo, 2003;de Silva et al, 2006;Gudmundsson, 2008Gudmundsson, , 2012Gottsmann et al, 2009;Gregg et al, 2012), and (4) large eruptions may tap multiple and distinct melt sources and crystal populations (including phenocrysts, antecrysts and xenocrysts, e.g., Maughan et al, 2002;Ellis et al, 2010;Wright et al, 2011;Allan et al, 2012;Cooper et al, 2012;Ellis and Wolff, 2012;Vinkler et al, 2012...…”

Is Efate (Vanuatu, SW Pacific) a result of subaerial or submarine eruption? An alternative model for the 1 Ma Efate Pumice Formation

“…Increasing numbers of silicic volcanoes have been identified in island arcs [1][2][3][4][5]. The emplacement of these silicic eruptives is of considerable interest because it not only 306 Brought to you by | MIT Libraries Authenticated Download Date | 5/11/18 5:01 PM provides data on the magmatic, tectonic and geomorphic environment of the volcanic arc at the time of eruption but also the types and levels of potential volcanic hazards, e.g.…”