The effect of oxygen fugacity on the rheological evolution of crystallizing basaltic melts

S. Kolzenburg*, D. Di Genova, D. Giordano, K. U. Hess, D. B. Dingwell

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

18 Citations (Scopus)
225 Downloads (Pure)

Abstract

Storage and transport of silicate melts in the Earth's crust and their emplacement on the planet's surface occur almost exclusively at sub-liquidus temperatures. At these conditions, the melts undergo crystallization under a wide range of cooling-rates, deformation-rates, and oxygen fugacities (fO2). Oxygen fugacity is known to influence the thermodynamics and kinetics of crystallization in magmas and lavas. Yet, its influence on sub-liquidus rheology remains largely uncharted. We present the first rheological characterization of crystallizing lavas along natural cooling paths and deformation-rates and at varying fO2. Specifically, we report on apparent viscosity measurements for two crystallizing magmatic suspensions 1) at log⁡fO2 of −9.15 (quartz–fayalite–magnetite buffer, QFM, −2.1) and 2) in air. These fugacities span a range of reduced to oxidized conditions pertinent to magma migration and lava emplacement. We find that: 1) crystallization at constant cooling-rates results in a quasi-exponential increase in the apparent viscosity of the magmatic suspensions until they achieve their rheological cut off temperature (Tcutoff), where the melt effectively solidifies 2) the rheological departure and Tcutoff increase with increasing fO2 and 3) increasing fO2 results in decreased crystallization-rates. Based on the experimental results and by comparison with previous rheological isothermal studies we propose a generalisation of the effect of fO2 on the dynamic rheological evolution of natural magmatic and volcanic suspensions. We further discuss the implications for magmatic transport in plumbing and storage systems (e.g. conduits, dikes and magma chambers) and during lava flow emplacement.

Original languageEnglish
Pages (from-to)21-32
Number of pages12
JournalEarth and Planetary Science Letters
Volume487
Early online date6 Feb 2018
DOIs
Publication statusPublished - 1 Apr 2018

Keywords

  • crystallization
  • disequilibrium processes
  • lava
  • magma
  • oxygen fugacity
  • rheology

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