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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Tracking the permeable porous network during strain-dependent magmatic flow
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Tracking the permeable porous network during strain-dependent magmatic flow

机译：在取决于应变的岩浆流中追踪渗透性多孔网络

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摘要

Rheological variations have been postulated as the cause of transitions from effusive to explosive volcanic eruption style. Rheology is integrally linked to the composition and textural state (porosity, crystallinity) of magma as well as the stress, temperature and strain rate operative during flow. This study characterises the rheological behaviour and, importantly, the evolution of physical properties of two magmas (with different crystallinity and porosity) from Volcan de Colima (Mexico) - a volcanic system known for its rapid fluctuations in eruption style. Magma samples deformed in a uniaxial press at a constant stress of 2.8,12 or 24 MPa, a constant temperature of 940-945 °C (comparable to upper conduit or lava dome conditions) to strains of 20 or 30% displayed different mechanical behaviour and significant differences in measured strain rates (10~(-2)-10~(-5) s~(-1)). The evolution of porosity, permeability, dynamic Young's modulus and dynamic Poisson's ratio illustrate a complex evolution of the samples manifested as strain-hardening, visco-elastic, constant-rate and strain-weakening deformation. Both magmas behave as shear-thinning non-Newtonian liquids and viscosity decreases as a function of strain. We find that strain localisation during deformation leads to the rearrangement and closure of void space (a combination of pores and cracks) followed by preferentially aligned fracturing (in the direction of the maximum principal stress) to form damage zones as well as densification of other areas. In a dome setting, highly viscous, low permeability magmas carry the potential to block volcanic conduits with a magma plug, resulting in the build-up of pressures in the conduit. Above a certain threshold of strain (dependent upon stress/strain rate), the initiation, propagation and coalescence of fractures leads to mechanical degradation of the magma samples, which then supersedes magmatic flow and crystal rearrangement as the dominant form of deformation. This results in lower apparent viscosities than those anticipated for magma of such crystallinity, especially at high strain rates. In a lava dome, this could result in dome collapse and the concomitant depressurisation could trigger an explosive eruption.
机译：流变学被认为是从火山喷发型向爆炸性喷发型过渡的原因。流变学与岩浆的组成和质地状态（孔隙度，结晶度）以及在流动过程中有效的应力，温度和应变率紧密相关。这项研究的特点是流变行为，以及重要的是两个来自火山岩（墨西哥）的岩浆（具有不同的结晶度和孔隙度）的物理特性的演变-火山系统以其喷发方式的快速波动而闻名。岩浆样品在单轴压力机中以2.8、12或24 MPa的恒定应力，940-945°C的恒定温度（与上部导管或熔岩穹顶条件相比）变形至20％或30％的应变，表现出不同的力学行为，并且测量应变率的显着差异（10〜（-2）-10〜（-5）s〜（-1））。孔隙率，渗透率，动态杨氏模量和动态泊松比的演变说明了样品的复杂演变，表现为应变硬化，粘弹性，恒定速率和应变弱化变形。两种岩浆均表现为剪切稀化的非牛顿液体，并且粘度随应变而降低。我们发现，变形过程中的应变局部化会导致空隙空间的重新排列和闭合（孔隙和裂缝的组合），随后优先排列的裂缝（沿最大主应力的方向）形成损坏区域以及其他区域的致密化。在穹顶环境中，高粘度，低渗透性岩浆具有利用岩浆塞堵塞火山岩管道的潜力，从而导致管道中压力的累积。超过一定的应变阈值（取决于应力/应变率），裂缝的发生，传播和合并会导致岩浆样品的机械降解，然后取代岩浆流和晶体重排，成为变形的主要形式。这导致比这种结晶性的岩浆预期的更低的表观粘度，特别是在高应变速率下。在熔岩穹顶中，这可能导致穹顶坍塌，并且随之而来的降压可能引发爆炸性喷发。

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  • 来源
    《Journal of Volcanology and Geothermal Research》 |2013年第15期|117-126|共10页
  • 作者

    J.E. Kendrick; Y. Lavallee; K.-U. Hess; M.J. Heap; H.E. Gaunt; P.G. Meredith; D.B. Dingwell;

  • 作者单位

    Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universitaet, Theresienstr. 41, 80333 Munich, Germany,Department of Earth, Ocean and Ecological Sciences, School of Environmental Sciences, University of Liverpool, Liverpool L69 3BX, United Kingdom;

    Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universitaet, Theresienstr. 41, 80333 Munich, Germany,Department of Earth, Ocean and Ecological Sciences, School of Environmental Sciences, University of Liverpool, Liverpool L69 3BX, United Kingdom;

    Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universitaet, Theresienstr. 41, 80333 Munich, Germany;

    Laboratoire de Deformation des Roches, Equipe de Geophysique Experimentale, Institut de Physique de Globe de Strasbourg (UMR 7516 CNRS, Universite de Strasbourg/EOST), 5 rue Rene Descartes, 67084 Strasbourg cedex, France;

    Rock & Ice Physics Laboratory, Department of Earth Sciences, University College London, Cower Street, London, United Kingdom;

    Rock & Ice Physics Laboratory, Department of Earth Sciences, University College London, Cower Street, London, United Kingdom;

    Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universitaet, Theresienstr. 41, 80333 Munich, Germany;

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  • 原文格式 PDF
  • 正文语种 eng
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  • 关键词

    Magma; Deformation; Rheology; Viscosity; Strain localization; Damage;

    机译：岩浆;形变;流变学粘度;应变局部化;损伤;

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