Silicate melt inclusions in the cumulate minerals of gabbroic nodules from Stromboli Volcano (Aeolian Islands, Italy): main components of the fluid phase and crystallization temperatures E. SALVIOLI-MARIANI 1, *, M. MATTIOLI 2 , A. RENZULLI 2 AND G. SERRI 1 1 Dipartimento di Scienze della Terra, Universita ` di Parma, Parco Area delle Scienze 157/A, I-43100 Parma, Italy 2 Istituto di Vulcanologia e Geochimica, Universita ` di Urbino, localita ` Crocicchia, I-61029 Urbino, Italy ABSTRACT The studied gabbroic nodules occurring in the Petrazza pyroclastic rocks consist mainly of plagioclase (An 95À87 ), olivine (Fo 83-73 ) and clinopyroxene (Mg# 90À77), with subordinate opaques (Ti-magnetite) and amphibole (Mg-hastingsite), which constitute the cumulate minerals. Interstitial material has a relatively high, but variable, degree of vesicularity and consists of variable amounts of glass and quenched crystals of plagioclase (An 71À55 ), amphibole, clinopyroxene and rare biotite, olivine and opaques. Silicate melt inclusions are abundant in the cumulate minerals, but complete homogenization to melt has been observed only in the inclusions occurring in clinopyroxene, where the temperatures of homogenization vary from 1134 to 1190ºC. Microthermometric investigations of fluid inclusions and of the shrinkage bubble of the melt inclusions suggest that the magma contained CO 2 . The apparent scarcity of H 2 O indicates that this component was strongly partitioned into the magma at the time of crystallization of the investigated minerals; this is further supported by the occurrence of (1) daughter biotite- and amphibole-bearing inclusions which show that the H 2 O activity in the magma was sufficiently high to allow their crystallization; and (2) calcic plagioclase (An 95À87 ) which can be crystallized from a high-alumina basaltic magma at pressure 42 kbar, temperatures in the range 1050À1100ºC and in the presence of 3À4 wt.% of water (MELTS software simulations). The composition of the melt inclusions suggests that the hosting plagioclase, olivine and clinopyroxene crystallized from slightly different batches of magma. The S content in the melt inclusions of clinopyroxene and olivine is high (up to 0.41 wt.%). The presence of Fe-Cu(-Ni)-rich blebs of sulphide in plagioclase, olivine, amphibole, and locally in the melt inclusions too, further supports the important role of sulphur in the primitive magmas of the investigated gabbros. Small differences in redox conditions or in the Fe content of the melts favoured S mobilization as sulphide. KEYWORDS: silicate melt inclusions, fluid inclusions, volatile components, gabbroic nodules, pyroclastic rocks, Petrazza, Stromboli volcano, Aeolian Islands, Italy. Introduction THE occurrence of relatively abundant nodules of variable lithology and texture in some pyroclastic sequences and lava flows of the Stromboli volcano has been discussed by many authors (Honnorez and Keller, 1968; Hornig-Kjarsgaard et al., 1993; Renzulli and Santi, 1997; Mattioli et al., 2002; Renzulli et al., 2001). Gabbroic nodules with cumulate texture are particularly abundant in the Petrazza pyroclastic sequence (Mattioli et al., 2002). This pyroclastic series belongs to one of the oldest subaerial volcano-stratigraphic units of Stromboli (Paleostromboli I; Hornig-Kjarsgaard et al., 1993), and consists of well sorted air-fall deposits with minor surges, flow deposits and intercalated lahars. The gabbroic nodules investi- gated are from the top layer of an orange fall unit (up to 20 m thick) where the amphibole-bearing pumiceous scoria has a high-K andesite composi- tion (La Petrazza, ENE shore of Stromboli island, # 2002 The Mineralogical Society * E-mail: salvioli@unipr.it DOI: 10.1180/0026461026660071 Mineralogical Magazine, December 2002, Vol. 66(6), pp. 969–984