A large K-foiditic hydromagmatic eruption from the early activity of the Alban Hills Volcanic District, Italy

摘要: In this paper we discuss the uncommon case of an energetic, pyroclastic-flow-forming eruption with a SiO2-poor (42–45 wt.%), K-foiditic magma composition. The Trigoria-Tor de' Cenci Tuff (TTC; 561 ka) is product first large-scale explosive event (of order 1–10 km3 erupted products) in Alban Hills Volcanic District, near city Rome, Italy. After initial Plinian phase that produced scoria fall horizon, pyroclastic current activity emplaced ash deposits leucite-bearing juvenile lapilli. abundance accretionary lapilli, most distinctive feature these deposits, together high degree fragmentation, minute lithic inclusions and morphology particles, indicates hydromagmatic character for part eruption. absence vent-derived carbonate clasts from deep regional aquifer cognate fragments suggest interaction external water involved surficial older volcanic terrains. Perhaps striking aspect TTC composition pre-eruptive melt, which, to our knowledge, unique among events comparable size elsewhere world. system feeding was controlled mainly by leucite+clinopyroxene fractionation under aH2O<1 conditions. low SiO2 prevented plagioclase K-feldspar crystallization. depth chamber can be estimated at 3–6 km within substrate. contrast other major eruptions Hills, volatile exsolution due crystallization not seen as main mechanism driving We behaviour early magmatic resulted rapid decompression seismic magma–water succeeding phase.