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Fractional crystallization of primitive, hydrous arc magmas: an experimental study at 0.7GPa

Nandedkar, Rohit ; Ulmer, Peter ; Müntener, Othmar

In: Contributions to Mineralogy and Petrology, 2014, vol. 167, no. 6, p. 1-27

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    Title
    • Fractional crystallization of primitive, hydrous arc magmas: an experimental study at 0.7GPa
    Author
    • Nandedkar, Rohit. Institute of Geochemistry and Petrology, ETH, Clausiusstrasse 25, 8092, Zürich, Switzerland
    • Ulmer, Peter. Institute of Geochemistry and Petrology, ETH, Clausiusstrasse 25, 8092, Zürich, Switzerland
    • Müntener, Othmar. Institute of Earth Sciences, Géopolis 4897, 1015, Lausanne, Switzerland
    Document Type
    • Postprint
    Language
    • English
    Published in
    • Contributions to Mineralogy and Petrology, 2014, vol. 167, no. 6, p. 1-27. Springer Berlin Heidelberg
    Other Version
    OAI-PMH Identifier
    • oai:doc.rero.ch:326181
    Summary
    Differentiation of mantle-derived, hydrous, basaltic magmas is a fundamental process to produce evolved intermediate to SiO2-rich magmas that form the bulk of the middle to shallow continental and island arc crust. This study reports the results of fractional crystallization experiments conducted in a piston cylinder apparatus at 0.7 GPa for hydrous, calc-alkaline to arc tholeiitic magmas. Fractional crystallization was approached by synthesis of starting materials representing the liquid composition of the previous, higher temperature experiment. Temperatures ranged from near-liquidus at 1,170°C to near-solidus conditions at 700°C. H2O contents varied from 3.0 to more than 10 wt%. The liquid line of descent covers the entire compositional range from olivine-tholeiite (1,170°C) to high-silica rhyolite (700°C) and evolves from metaluminous to peraluminous compositions. The following crystallization sequence has been established: olivine→clinopyroxene→plagioclase, spinel→orthopyroxene, amphibole, titanomagnetite→apatite→quartz, biotite. Anorthite-rich plagioclase and spinel are responsible for a marked increase in SiO2-content (from 51 to 53wt%) at 1,040°C. At lower temperatures, fractionation of amphibole, plagioclase and Fe-Ti oxide over a temperature interval of 280°C drives the SiO2 content continuously from 53 to 78wt%. Largest crystallization steps were recorded around 1,040°C and at 700°C. About 40% of ultramafic plutonic rocks have to crystallize to generate basaltic-andesitic liquids, and an additional 40% of amphibole-gabbroic cumulate to produce granitic melts. Andesitic liquids with a liquidus temperature of 1,010°C only crystallize 50% over an 280°C wide range to 730°C implying that such liquids form mobile crystal mushes (<50% crystals) in long-lived magmatic systems in the middle crust, allowing for extensive fractionation, assimilation and hybridization with periodic replenishment of more mafic magmas from deeper magma reservoirs.