Single clinopyroxene crystals from four different volcanic suites on Stromboli (Aeolian Islands, Italy) were studied by X-ray diffraction and microprobe analysis in order to obtain information on the relations between clinopyroxene crystal chemistry and the petrology of the host rocks, and to provide comparisons with the nearby islands of Vulcano, Filicudi and SaIina. Crystal chemical study reveals the coexistence on Stromboli of rocks with two clinopyroxene compositions with C2/c symmetry, diopside and augite, both of which show wide ranges in structural and chemical parameters. Unit cell and M1 site volumes are relatively large, a feature that is indicative of low crystallization pressure, as already observed in clinopyroxene from Vulcano and Salina. Comparable clinopyroxene from Filicudi are characterized by lower volumes and interpreted as having crystallized in a deeper magma chamber (Malgarotto et al., 1993). The intracrystalline Mg-Fe2+ ordering reaction shows closure temperatures for Stromboli clinopyroxene ranging between 620 and 1100 degrees C. This wide range indicates different cooling rates related to eruptive mechanisms.
CRYSTAL-CHEMISTRY OF STROMBOLI CLINOPYROXENE - A COMPARISON WITH ANALOGS FROM OTHER AEOLIAN ISLANDS (ITALY)
PASQUAL, DARIA;MOLIN, GIANMARIO;
1995
Abstract
Single clinopyroxene crystals from four different volcanic suites on Stromboli (Aeolian Islands, Italy) were studied by X-ray diffraction and microprobe analysis in order to obtain information on the relations between clinopyroxene crystal chemistry and the petrology of the host rocks, and to provide comparisons with the nearby islands of Vulcano, Filicudi and SaIina. Crystal chemical study reveals the coexistence on Stromboli of rocks with two clinopyroxene compositions with C2/c symmetry, diopside and augite, both of which show wide ranges in structural and chemical parameters. Unit cell and M1 site volumes are relatively large, a feature that is indicative of low crystallization pressure, as already observed in clinopyroxene from Vulcano and Salina. Comparable clinopyroxene from Filicudi are characterized by lower volumes and interpreted as having crystallized in a deeper magma chamber (Malgarotto et al., 1993). The intracrystalline Mg-Fe2+ ordering reaction shows closure temperatures for Stromboli clinopyroxene ranging between 620 and 1100 degrees C. This wide range indicates different cooling rates related to eruptive mechanisms.
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