Gas-driven filter pressing in magmas: Insights into in-situ melt segregation from crystal mushes
Gas-driven filter pressing in magmas: Insights into in-situ melt segregation from crystal mushes
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DOI：
10.1130/g36766.1
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发表时间：
2015-08
期刊：
影响因子：
5.8
通讯作者：
M. Pistone;F. Arzilli;K. Dobson;Benoît Cordonnier;E. Reusser;P. Ulmer;F. Marone;A. Whittington;Lucia;Mancini;J. L. Fife;Jonathan D. Blundy
中科院分区：
文献类型：
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作者：
M. Pistone;F. Arzilli;K. Dobson;Benoît Cordonnier;E. Reusser;P. Ulmer;F. Marone;A. Whittington;Lucia;Mancini;J. L. Fife;Jonathan D. Blundy
气体驱动的压滤是从挥发物饱和的晶体糊状物中排出熔体的过程，由气体压力的积累和随后的释放引起。滤压作用被推断为在较浅深度（<10 km）通过移动熔体和气体相对于固体、结晶框架的岩浆分馏中起主要作用。然而，这一过程运作的岩浆条件仍然缺乏约束。我们提出了新的实验数据，说明了糊状物的晶体含量如何影响气体驱动的压滤分离熔体的能力。使用具有高空间分辨率（3 μm/像素）和时间分辨率（每个三维数据集108 s）的原位高温（500-800 °C）同步加速器X射线断层扫描显微镜研究了具有宽堆积范围（34-80 vol%晶体）的含水单花岗岩（熔体中2.1 wt%的水）和英安岩（熔体中4.2 wt%的水）晶体浆。我们的实验结果表明，气体驱动的压滤操作仅低于最大包装的气泡和晶体（1074体积%）。在这个阈值以上，糊状物倾向于破裂，气体通过破裂逸出。因此，气体驱动的压滤的效率被提升到接近渗流阈值，并且在糊状物相对于压力的积聚和熔体的排出缓慢膨胀的情况下。这些观测结果为地壳内可喷发的贫结晶岩浆的产生提供了一个可能的解释。
Gas-driven filter pressing is the process of melt expulsion from a volatile-saturated crystal mush, induced by the buildup and subsequent release of gas pressure. Filter pressing is inferred to play a major role in magma fractionation at shallow depths (<10 km) by moving melt and gas relative to the solid, crystalline framework. However, the magmatic conditions at which this process operates remain poorly constrained. We present novel experimental data that illustrate how the crystal content of the mush affects the ability of gas-driven filter pressing to segregate melt. Hydrous haplogranite (2.1 wt% water in the melt) and dacite (4.2 wt% water in the melt) crystal mushes, with a wide range of crystallinities (34–80 vol% crystals), were investigated using in-situ, high-temperature (500–800 °C) synchrotron X-ray tomographic microscopy with high spatial (3 μm/pixel) and temporal resolution (∼8 s per three-dimensional data set). Our experimental results show that gas-driven filter pressing operates only below the maximum packing of bubbles and crystals (∼74 vol%). Above this threshold, the mush tends to fracture and gas escapes via fractures. Therefore, the efficiency of gas-driven filter pressing is promoted close to the percolation threshold and in situations where a mush inflates slowly relative to build-up of pressure and expulsion of melt. Such observations offer a likely explanation for the production of eruptible, crystal-poor magmas within Earth’s crust.