标题： 熔浆在圆柱形通道中起泡增强的渗透性发展 显示英文标题

标题： Shear-enhanced permeability development of magma vesiculating in cylindrical conduits

摘要： 在岩浆起泡过程中，当生长的气泡开始形成连接网络时，渗透性得以建立，这使得流体能够渗透。这种渗透阈值控制着岩浆上升速率和挥发性脱气速率之间的相对关系，进而决定了喷发类型。渗透主要受控于总孔隙度和剪切条件。 我们在空间受限的圆柱形导管几何形状中对流纹玻璃进行了起泡实验。样品经历的剪切量通过改变样品直径和围压直径来控制，以允许不同程度的自由（各向同性）随后是受限（各向异性）膨胀。孔隙度的各向异性发展与流动方向平行。 我们测量了起泡样品的总体孔隙度、连通孔隙度和渗透性。我们观察到两种行为模式：1）由各向同性膨胀主导的样品，在渗透开始时对应剪切变形的开始；2）由各向异性膨胀主导的样品，显示出较低的渗透阈值（<20%），即使孔隙度增加，渗透性也几乎保持恒定。我们发现连通孔隙度与渗透性之间有很好的相关性，剪切和未剪切样品具有不同的趋势。 气泡化岩浆中各向异性的发育在岩浆网络中普遍存在，我们的数据强调了在研究渗透阈值时考虑原位剪切条件的重要性。 显示英文摘要

摘要： During magma vesiculation, permeability is established when growing bubbles begin to form connected networks, which allow fluids to percolate. This percolation threshold controls the relative rates between magma ascent and volatile exsolution, which in turn dictate eruptive style. Percolation is controlled primarily by total vesicularity and shear conditions. We performed vesiculation experiments on rhyolitic glass in a spatially confined, cylindrical, conduit-like geometry. The amount of shear experienced by the sample is controlled by varying the sample and confining diameters to allow for various degrees of free (isotropic) followed by confined (anisotropic) expansion. Pore anisotropy develops sub-parallel to the flow direction. We measure the total and connected porosity and permeability of the vesiculated samples. We observe two regimes of behavior for samples dominated by 1) isotropic expansion, in which the onset of percolation corresponds with the beginning of shear deformation and 2) anisotropic expansion which shows low percolation thresholds (<20%) with a near-constant permeability even with increasing porosity. We find a good correlation between connected porosity and permeability, with distinct trends for sheared and unsheared samples. The development of anisotropy in vesiculating magmas is ubiquitous in magmatic networks and our data highlight the importance of considering the in situ shear conditions when investigating the percolation threshold.