Quantifying magma segregation in dykes

P. Yamato, T. Duretz, D. A. May, R. Tartèse

    Research output: Contribution to journalArticlepeer-review

    Abstract

    The dynamics of magma flow is highly affected by the presence of a crystalline load. During magma ascent, it has been demonstrated that crystal-melt segregation constitutes a viable mechanism for magmatic differentiation. Moreover, crystal-melt segregation during magma transport has important implications not only in terms of magma rheology, but also in terms of differentiation of the continental crust. However, the influences of the crystal volume percentage (ϕ), of their geometry, their size and their density on crystal-melt segregation are still not well constrained. To address these issues, we performed a parametric study using 2D direct numerical simulations, which model the ascension of a crystal-bearing magma in a vertical dyke. Using these models, we have characterised the amount of segregation as a function of different physical properties including ϕ, the density contrast between crystals and the melt phase (δ. ρ), the size of the crystals (Ac) and their aspect ratio (R). Results show that small values of R do not affect the segregation. In this case, the amount of segregation depends upon four parameters. Segregation is highest when δ. ρ and Ac are large, and lowest for large pressure gradient (Pd) and/or large values of dyke width (Wd). These four parameters can be combined into a single one, the Snumber, which can be used to quantify the amount of segregation occurring during magma ascent. Based on systematic numerical modelling and dimensional analysis, we provide a first order scaling law which allows quantification of the segregation for an arbitrary Snumber and ϕ, encompassing a wide range of typical parameters encountered in terrestrial magmatic systems. Although developed in a simplified system, this study has strong implications regarding our understanding of crystal segregation processes during magma transport. Our first order scaling law allows to immediately determine the amount of crystal-melt segregation occurring in any given magmatic dyke system.

    Original languageEnglish
    Pages (from-to)132-147
    Number of pages16
    JournalTectonophysics
    Volume660
    DOIs
    Publication statusPublished - 7 Oct 2015

    Keywords

    • Differentiation
    • Dykes
    • Magma dynamics
    • Numerical modelling
    • Segregation

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