In a paper published in 1920, Bowen conceived of a situation where forces acting on a crystalline mesh could extract the liquid phase from the solid, and in doing so cause variations in chemistry distinct from the purely gravitational effects of fractional crystallisation. His paper was a call-to-arms to explore the role of deformation as a cause of variation in igneous rocks, but was never followed-up in a rigorous way. Inspired by this, we have developed a quantitative model showing how shear deformation of a crystallised dense magma ( ϕ > 70%) with poro-elastic properties is analogous to a granular material. The critical link between the mechanics and associated compositional changes of the melt is the degree to which the crystallising magma undergoes dilation (volume increase) during shear. It is important to note that the effect can only take place after the initial loose solid material has undergone mechanical compaction such that the grains comprising the rigid skeleton are in permanent contact. Under these conditions, the key material parameters governing the dilatancy effect are the physical permeability, mush strength, the shear modulus and the contact mechanics and geometry of the granular assemblage. Calculations show that dilation reduces the interstitial fluid (melt) pressure causing, in Bowen’s words, “the separation of crystals and mother liquor” via a suction effect. At shear strain rates in excess of the tectonic background, deformation-induced melt flow can redistribute chemical components and heat between regions of crystallising magma with contrasting rheological properties, at velocities far in excess of diffusion or buoyancy forces, the latter of course the driving force behind fractional crystallisation and viscous compaction. Influx of hotter, less evolved melt drawn internally from the same magma body into regions where crystallisation is more advanced (auto-intrusion), may result in reverse zoning and/or resorption of crystals. Because dilatancy is primarily a mechanical effect independent of melt composition, evolved, chemically distinct melt fractions removed at this late stage may explain miarolitic alkaline rocks, intrusive granophyres in basaltic systems and late stage aplites and pegmatites in granites (discontinuous variations), as proposed by Bowen. Post-failure instabilities include hydraulic rupture of the mush along shear zones governed by the angles of dilation and internal friction. On the macro-scale, a combination of dilatancy and fracturing may provide a means to extract large volumes of chemically evolved melt from mush columns on short (< 1000 year) geological timescales.

中文翻译：

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火成因变形分化

在 1920 年发表的一篇论文中，鲍文设想了一种情况，即作用在结晶网格上的力可以从固体中提取液相，并且这样做会导致化学变化，这与分步结晶的纯重力效应不同。他的论文是探索变形作为火成岩变化原因的作用的号召，但从未以严格的方式进行跟进。受此启发，我们开发了一个定量模型，显示具有多孔弹性特性的结晶致密岩浆 ( ϕ > 70%) 的剪切变形如何类似于颗粒材料。熔体力学与相关成分变化之间的关键联系是结晶岩浆在剪切过程中膨胀（体积增加）的程度。重要的是要注意，只有在初始松散固体材料经过机械压实后才会发生这种效应，从而使构成刚性骨架的颗粒永久接触。在这些条件下，控制剪胀效应的关键材料参数是物理渗透性、泥浆强度、剪切模量以及颗粒组合的接触力学和几何形状。计算表明，膨胀会降低间隙液（熔体）压力，用鲍文的话来说，通过抽吸效应导致“晶体和母液的分离”。在超过构造背景的剪切应变率下，变形引起的熔体流动可以在具有对比流变特性的结晶岩浆区域之间重新分配化学成分和热量，在远远超过扩散或浮力的速度下，后者当然是部分结晶和粘性压实背后的驱动力。从同一岩浆体内部抽取的较热、较少演化的熔体流入结晶更先进的区域（自动侵入），可能导致晶体的反向分区和/或再吸收。因为剪胀主要是一种独立于熔体成分的机械效应，在这个晚期移除的演化的、化学上不同的熔体部分可以解释玄武岩系统中的火山岩、侵入岩和花岗岩中的晚期细长岩和伟晶岩（不连续的变化），如由鲍文。破坏后的不稳定性包括糊状物沿受膨胀角和内摩擦角控制的剪切区的水力破裂。