Stress-driven melt segregation may have important geochemical and geophysical effects but remains a poorly understood process. Few constraints exist on the permeability and distribution of melt in deformed partially molten rocks. Here, we characterize the 3D melt network and resulting permeability of an experimentally deformed partially molten rock containing several melt-rich bands based on an X-ray microtomography data set. Melt fractions range from 0.08 to 0.28 in the ∼20-μm-thick melt-rich bands, and from 0.02 to 0.07 in the intervening ∼30-μm-thick regions. We simulated melt flow through subvolumes extracted from the reconstructed rock at five length scales ranging from the grain scale (3 μm) to the minimum length required to fully encompass two melt-rich bands (64 μm). At grain scale, few subvolumes contain interconnected melt, and permeability is isotropic. As the length scale increases, more subvolumes contain melt that is interconnected parallel to the melt bands, but connectivity diminishes in the direction perpendicular to them. Even if melt is connected in all directions, permeability is lower perpendicular to the bands, in agreement with the elongation of melt pockets. Permeability parallel to the bands is proportional to melt fraction to the power of an exponent that increases from ∼2 to 5 with increasing length scale. The permeability in directions parallel to the bands is comparable to that for an isotropic partially molten rock. However, no flow is possible perpendicular to the bands over distances similar to the band spacing. Melt connectivity limits sample scale melt flow to the plane of the melt-rich bands.

中文翻译：

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应力驱动熔体偏析对熔体取向、熔体连通性和各向异性渗透率的影响

应力驱动的熔体偏析可能具有重要的地球化学和地球物理效应，但仍然是一个人们知之甚少的过程。变形部分熔融岩石中熔体的渗透性和分布几乎不存在任何限制。在这里，我们基于 X 射线显微断层扫描数据集描述了包含多个熔体丰富带的实验变形部分熔融岩石的 3D 熔体网络和由此产生的渗透率。在~20μm厚的熔体丰富带中，熔体分数的范围为0.08至0.28，在中间的~30μm厚的区域中，熔体分数的范围为0.02至0.07。我们以五个长度尺度模拟了从重建岩石中提取的子体积的熔体流动，范围从晶粒尺度 (3 μm) 到完全包含两个富含熔体带所需的最小长度 (64 μm)。在晶粒尺度上，很少有子体积包含互连的熔体，并且渗透率是各向同性的。随着长度尺度的增加，更多的子体积包含平行于熔体带互连的熔体，但连通性在垂直于它们的方向上减弱。即使熔体在所有方向上连接，垂直于带的渗透性也较低，这与熔体袋的伸长一致。平行于条带的渗透率与熔体分数的指数次方成正比，随着长度尺度的增加，该指数从~2增加到5。平行于条带方向的渗透率与各向同性部分熔融岩石的渗透率相当。然而，在与带间距相似的距离上垂直于带的流动是不可能的。熔体连通性限制了样品规模熔体流向富熔体带的平面。