The Campanian Ignimbrite southern Italy geochemi

Authors: Lucia Pappalardo Luisa Ottolini Giuseppe Mastrolorenzo

Publish Date: 2007/12/11

Volume: 156, Issue: 1, Pages: 1-26

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Abstract

More than ca 100 km3 of nearly homogeneous crystalpoor phonolite and ca 100 km3 of slightly zoned trachyte were erupted 39 ka during the Campanian Ignimbrite super eruption the most powerful in the Neapolitan area Partition coefficient calculations equilibrium mineral assemblages glass compositions and texture were used to reconstruct compositional thermal and pressure gradients in the preeruptive reservoir as well as timing and mechanisms of evolution towards magma chamber overpressure and eruption Our petrologic data indicate that a wide silllike trachytic magma chamber was active under the Campanian Plain at 25 kbar before CI eruption Thermal exchange between high liquidus 1199°C trachytic sill and cool country rocks caused intense undercooling driving a catastrophic and fast 102 years in situ fractional crystallization and crustal assimilation that produced a water oversaturated phonolitic cap and an overpressure in the chamber that triggered the super eruption This process culminated in an abrupt reservoir opening and in a fast singlestep high decompression Sanidine phenocrysts crystal size distributions reveal high differentiation rate thus suggesting that such a silllike magmatic system is capable of evolving in a very short time and erupting suddenly with only shortterm warningThe authors wish to thank M Serracino CNRIGAG Rome for the kind assistance during the electron microprobe analyses We are thankful to G Della Ventura Università “Roma Tre” Rome Italy for his help during the FTIR analyses The comments and suggestions of two anonymous referees are greatly appreciated

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