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Authors: Piochi, M.* 
Ayuso, R. A.* 
De Vivo, B.* 
Somma, R.* 
Title: Crustal contamination and crystal entrapment during polybaric magma evolution at Mt.Somma-Vesuvius volcano, Italy: Geochemical and Sr isotope evidence
Journal: Lithos 
Series/Report no.: /86 (2006) Elsevier
Issue Date: 2006
DOI: 10.1016/j.lithos.2005.05.009
Keywords: Mt. Somma–Vesuvius volcano
Sr isotopes
Crustal contamination
Mantle source
Phenocryst entrapment
Subject Classification04. Solid Earth::04.08. Volcanology::04.08.03. Magmas 
04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks 
05. General::05.02. Data dissemination::05.02.01. Geochemical data 
Abstract: New major and trace element analyses and Sr-isotope determinations of rocks from Mt. Somma–Vesuvius volcano produced from 25 ky BP to 1944 AD are part of an extensive database documenting the geochemical evolution of this classic region. Volcanic rocks include silica undersaturated, potassic and ultrapotassic lavas and tephras characterized by variable mineralogy and different crystal abundance, as well as by wide ranges of trace element contents and a wide span of initial Sr-isotopic compositions. Both the degree of undersaturation in silica and the crystal content increase through time, being higher in rocks produced after the eruption at 472 AD (Pollena eruption). Compositional variations have been generally thought to reflect contributions from diverse types of mantle and crust. Magma mixing is commonly invoked as a fundamental process affecting the magmas, in addition to crystal fractionation. Our assessment of geochemical and Srisotopic data indicates that compositional variability also reflects the influence of crustal contamination during magma evolution during upward migration to shallow crustal levels and/or by entrapment of crystal mush generated during previous magma storage in the crust. Using a variant of the assimilation fractional crystallization model (Energy Conservation– Assimilation Fractional Crystallization; [Spera and Bohrson, 2001. Energy-constrained open-system magmatic processes I: General model and energy-constrained assimilation and fractional crystallization (EC–AFC) formulation. J. Petrol. 999– 1018]; [Bohrson, W.A. and Spera, F.J., 2001. Energy-constrained open-system magmatic process II: application of energyconstrained assimilation–fractional crystallization (EC–AFC) model to magmatic systems. J. Petrol. 1019–1041]) we estimated the contributions from the crust and suggest that contamination by carbonate rocks that underlie the volcano (2 km down to 9–10 km) is a fundamental process controlling magma compositions at Mt. Somma–Vesuvius in the last 8 ky BP. Contamination in the mid- to upper crust occurred repeatedly, after the magma chamber waxed with influx of new mantle- and crustal-derived magmas and fluids, and waned as a result of magma withdrawal and production of large and energetic plinian and subplinian eruptions.
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