One of the outstanding problems in understanding the behavior of intermediate-to-silicic magmatic systems is the mechanism(s) by which large volumes of crystal-poor rhyolite can be extracted from crystal-rich mushy storage zones in the mid-deep crust. The mechanisms commonly invoked are hindered settling, micro-settling, and compaction. The concept of micro-settling involves extraction of grains from a crystal framework during Ostwald ripening and has been shown to be non-viable in the metallic systems for which it was originally proposed. Micro-settling is also likely to be insignificant in silicic mushes, because ripening rates are slow for quartz and plagioclase, contact areas between grains in a crystal mush are likely to be large, and abundant low-angle grain boundaries promote grain coalescence rather than ripening. Published calculations of melt segregation rates by hindered settling (Stokes settling in a crystal-rich system) neglect all but fluid dynamical interactions between particles. Because tabular silicate minerals are likely to form open, mechanically coherent, frameworks at porosities as high as ~ 75%, settling of single crystals is only likely in very melt-rich systems. Gravitationally-driven viscous compaction requires deformation of crystals by either dissolution–reprecipitation or dislocation creep. There is, as yet, no reported microstructural evidence of extensive, syn-magmatic, internally-generated, viscous deformation in fully solidified silicic plutonic rocks. If subsequent directed searches do not reveal clear evidence for internally-generated buoyancy-driven melt segregation processes, it is likely that other factors, such as rejuvenation by magma replenishment, gas filter-pressing, or externally-imposed stress during regional deformation, are required to segregate large volumes of crystal-poor rhyolitic liquids from crustal mushy zones.

中文翻译：

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硅晶糊的熔体分离：对可能机制及其微观结构记录的批判性评估

了解中硅质岩浆系统行为的突出问题之一是从中深部地壳富含晶体的糊状储存区中提取大量贫晶体流纹岩的机制。通常采用的机制是受阻沉降、微沉降和压实。微沉降的概念涉及在奥斯特瓦尔德成熟过程中从晶体框架中提取晶粒，并且已被证明在最初提出的金属体系中是不可行的。硅质糊状物中的微沉降也可能不显着，因为石英和斜长石的成熟速率很慢，晶糊中颗粒之间的接触面积可能很大，并且丰富的低角度晶界促进颗粒聚结而不是成熟。已发表的受阻沉降（在富含晶体的系统中的斯托克斯沉降）对熔体偏析率的计算忽略了颗粒之间除了流体动力学相互作用之外的所有相互作用。由于板状硅酸盐矿物很可能在孔隙率高达约 75% 时形成开放的、机械连贯的框架，因此单晶的沉降只可能在熔体非常丰富的系统中发生。重力驱动的粘性压实需要通过溶解-再沉淀或位错蠕变使晶体变形。迄今为止，还没有关于完全凝固的硅质深成岩中广泛的、同岩浆的、内部产生的粘性变形的微观结构证据的报道。如果后续的定向搜索没有揭示内部产生的浮力驱动熔体偏析过程的明确证据，则可能需要其他因素，例如通过岩浆补充、气体滤压或区域变形过程中外部施加的应力进行再生从地壳糊状区域中分离出大量缺乏晶体的流纹岩液体。