Mineralogy and Petrology (2003) 79: 99–125 DOI 10.1007/s00710-003-0004-6 Pre-eruptive geochemistry of the ignimbrite-forming magmas of the Campanian Volcanic Zone, Southern Italy, determined from silicate melt inclusions J. D. Webster 1 , F. Raia 2 , C. Tappen 1 , and B. De Vivo 3 1 Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY, USA 2 Department of Earth and Atmospheric Sciences, City College of New York, NY, USA 3 Dipartimento di Geofisica e Vulcanologia, Universita di Napoli Federico II, Naples, Italy Received July 15, 2002; revised version accepted March 27, 2003 Editorial handling: R. Scandone Summary The Campanian Ignimbrite rock samples include two compositionally distinct populations of clinopyroxene phenocrysts, and the entrapped MI (melt inclusions) are also different in composition. The cores of the more MgO-enriched phenocrysts carry basaltic trachyandesite MI that contain >6 wt.% MgO, whereas other phenocrysts contain MI with <4 wt.% MgO. The MgO-enriched MI also contain comparatively greater abundances of F, CaO, TiO 2 ,P 2 O 5 , SO 2 , and Sr and show marginally higher ratios of (CaO=Al 2 O 3 ) than the low-MgO MI. Most of the high-MgO MI also contain comparatively more H 2 O. The MgO-enriched MI are restricted to diopsidic clinopy- roxenes and show minimal compositional variability, demonstrating that they were derived from a common magmatic source or sources. We interpret these MI to represent primary, mafic magma. In contrast, the more evolved, low-MgO melt inclusions, which are restricted to salitic clinopyroxenes, span the compositional range of trachyandesite to trachyte. The low-MgO fractions of Campanian Ignimbrite magma evolved via fractional crystallization with or without mingling or mixing with more primitive, high-MgO magma. Interestingly, the MI from the Giugliano sample also cluster into low-MgO and high-MgO fractions, and the evolutionary trends for major, minor, and trace elements mirror those exhibited by the Campanian Ignimbrite MI, suggesting that both magmas