In situ observation of the percolation threshold in multiphase magma analogues
Autor: | Colombier, M., Wadsworth, F. B., Scheu, B., Vasseur, J., Dobson, K. J., Cáceres, F., Allabar, A., Marone, F., Schlepütz, C. M., Dingwell, D. B., Earth and Environmental Sciences, Ludwig-Maximilians-Universität, Munich, Germany, Centre for Advanced Study, Ludwig-Maximilians-Universität, Munich, Germany, Department of Earth Sciences, Durham University, Durham, UK, Department of Geosciences, University of Tübingen, Tübingen, Germany, Swiss Light Source, Paul Scherer Institute, Villigen PSI, Switzerland |
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Rok vydání: | 2020 |
Předmět: |
010504 meteorology & atmospheric sciences
Bubble Crystal-rich magma Effusive-explosive transition 010502 geochemistry & geophysics 01 natural sciences Physics::Geophysics Viscosity Geochemistry and Petrology Percolation threshold ddc:550.724 Magma viscosity Porosity 0105 earth and related environmental sciences Coalescence (physics) Pore connectivity Outgassing Hysteresis Strombolian/Vulcanian eruptions Gas overpressure Strombolian eruption Dome-forming eruptions Overpressure Chemical physics TA170 Geology Research Article |
Zdroj: | Bulletin of Volcanology Bulletin of volcanology, 2020, Vol.82(4), pp.32 [Peer Reviewed Journal] |
ISSN: | 1432-0819 0258-8900 |
DOI: | 10.1007/s00445-020-1370-1 |
Popis: | Magmas vesiculate during ascent, producing complex interconnected pore networks, which can act as outgassing pathways and then deflate or compact to volcanic plugs. Similarly, in-conduit fragmentation events during dome-forming eruptions create open systems transiently, before welding causes pore sealing. The percolation threshold is the first-order transition between closed- and open-system degassing dynamics. Here, we use time-resolved, synchrotron-source X-ray tomography to image synthetic magmas that go through cycles of opening and closing, to constrain the percolation threshold ΦC at a range of melt crystallinity, viscosity and overpressure pertinent to shallow magma ascent. During vesiculation, we observed different percolative regimes for the same initial bulk crystallinity depending on melt viscosity and gas overpressure. At high viscosity (> 106 Pa s) and high overpressure (~ 1–4 MPa), we found that a brittle-viscous regime dominates in which brittle rupture allows system-spanning coalescence at a low percolation threshold (ΦC~0.17) via the formation of fracture-like bubble chains. Percolation was followed by outgassing and bubble collapse causing densification and isolation of the bubble network, resulting in a hysteresis in the evolution of connectivity with porosity. At low melt viscosity and overpressure, we observed a viscous regime with much higher percolation threshold (ΦC > 0.37) due to spherical bubble growth and lower degree of crystal connection. Finally, our results also show that sintering of crystal-free and crystal-bearing magma analogues is characterised by low percolation thresholds (ΦC = 0.04 – 0.10). We conclude that the presence of crystals lowers the percolation threshold during vesiculation and may promote outgassing in shallow, crystal-rich magma at initial stages of Vulcanian and Strombolian eruptions. Paul Scherrer Institut http://dx.doi.org/10.13039/501100004219 European Research Council http://dx.doi.org/10.13039/501100000781 NERC Deutsche Forschungsgemeinschaft |
Databáze: | OpenAIRE |
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