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In-situ degassing of natural crystal-bearing silicic magmas

Francisco Cáceres 1, Mathieu Colombier2, Alain Burgisser3, Rebecca deGraffenried4, Christian M. Schlepütz5, Pedro Valdivia6, Simon Thivet7, Bettina Scheu2, Janine Birnbaum2, Ruben M. Ruhekenya8, Daniel Weidendorfer2, Kai-Uwe Hess2, Donald B. Dingwell2

  • Affiliations: 1Facultad de Ciencias Básicas, Universidad Católica de Maule, Talca, Chile; 2Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Munich, Germany; 3University Grenoble Alpes, University Savoie Mont Blanc, Grenoble, France; 4Geological Sciences, University of Missouri, Columbia, USA; 5Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland; 6Bavarian Geoinstitute, Universität Bayreuth, Bayreuth, Germany; 7Department of Earth Sciences, Université de Genève, Geneva, Switzerland; 8Vrije Universiteit Amsterdam, Amsterdam, Netherlands

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 215

  • Programme No: 3.6.19

  • Theme 3 > Session 6

Abstract

Bubble growth dynamics in silicic magmas determine magma storage ability in the crust and its transport through the Earth's crust to the surface. Bubble formation and growth in magma is typically driven by magma decompression and/or heating upon ascent, where neighboring bubbles tend to interact, deform and/or coalesce during growth. Crystals are present in all natural magmas in variable quantities. However, the effect of different crystal types, sizes and shapes on the degassing dynamics of crystal-poor silicic magmas remains barely studied. In this work we explore bubble growth dynamics in different natural crystal-poor obsidians via heating experiments coupled with in-situ 4D visualization using time-resolved synchrotron-based X-ray tomography. Experiments show a clear control of crystals (phenocrysts and microlites) on bubble spatial distribution even at low crystal volume fractions. Coalescence is observed in phenocryst-bearing samples and bubble growth kinetics differ from those observed in phenocryst-free obsidian and predicted by bubble growth modelling. On the other hand, the distribution of oxides microlites seems to control the distribution of nucleated bubbles. These results shed light on the influence of different crystalline phases on the spatial distribution of bubbles. The time resolution of a few seconds allows us to capture highly transient bubble interactions that have consequences on the dynamics of magma degassing during ascent with potentially strong implications for eruptive behaviour.