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Erupted cumulate fragments in rhyolites from Lipari (Aeolian Islands)

Forni, Francesca ; Ellis, Ben ; Bachmann, Olivier ; Lucchi, Federico ; Tranne, Claudio ; Agostini, Samuele ; Dallai, Luigi

In: Contributions to Mineralogy and Petrology, 2015, vol. 170, no. 5-6, p. 1-18

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    Titre
    • Erupted cumulate fragments in rhyolites from Lipari (Aeolian Islands)
    Auteur
    • Forni, Francesca. Institute of Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, 8092, Zurich, Switzerland
    • Ellis, Ben. Institute of Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, 8092, Zurich, Switzerland
    • Bachmann, Olivier. Institute of Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, 8092, Zurich, Switzerland
    • Lucchi, Federico. Dipartimento di Scienze Biologiche, Geologiche e Ambientali (Sezione di Geologia), Università di Bologna, P.zza di Porta S. Donato, 1, 40126, Bologna, Italy
    • Tranne, Claudio. Dipartimento di Scienze Biologiche, Geologiche e Ambientali (Sezione di Geologia), Università di Bologna, P.zza di Porta S. Donato, 1, 40126, Bologna, Italy
    • Agostini, Samuele. CNR, Istituto di Geoscienze e Georisorse, Via G. Moruzzi 1, 56124, Pisa, Italy
    • Dallai, Luigi. CNR, Istituto di Geoscienze e Georisorse, Via G. Moruzzi 1, 56124, Pisa, Italy
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Contributions to Mineralogy and Petrology, 2015, vol. 170, no. 5-6, p. 1-18. Springer Berlin Heidelberg
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:332262
    Summary
    Over the last ~267ky, the island of Lipari has erupted magmas ranging in compositions from basaltic andesites to rhyolites, with a notable compositional gap in the dacite field. Bulk geochemical and isotopic compositions of the volcanic succession, in conjunction with major and trace elemental compositions of minerals, indicate that the rhyolites were dominantly generated via crystal fractionation processes, with subordinate assimilation. Radiogenic (Sr, Nd, and Pb) and stable (O) isotopes independently suggest ≤30% of crustal contamination with the majority of it occurring in mafic compositions, likely relatively deep in the system. Within the rhyolites, crystal-rich, K2O-rich enclaves are common. In contrast to previous interpretations, we suggest that these enclaves represent partial melting, remobilization and eruption of cumulate fragments left-over from rhyolite melt extraction. Cumulate melting and remobilization is supported by the presence of (1) resorbed, low-temperature minerals (biotite and sanidine), providing the potassic signature to these clasts, (2) reacted Fo-rich olivine, marking the presence of mafic recharge, (3) An38-21 plagioclase, filling the gap in feldspar composition between the andesites and the rhyolites and (4) strong enrichment in Sr and Ba in plagioclase and sanidine, suggesting crystallization from a locally enriched melt. Based on Sr-melt partitioning, the high-Sr plagioclase would require ~2300ppm Sr in the melt, a value far in excess of Sr contents in Lipari and Vulcano magmas (50-1532ppm) but consistent with melting of a feldspar-rich cumulate. Due to the presence of similar crystal-rich enclaves within the rhyolites from Vulcano, we propose that the eruption of remobilized cumulates associated with high-SiO2 rhyolites may be a common process at the Aeolian volcanoes, as already attested for a variety of volcanic systems around the world.