A model is presented whereby metamorphic parageneses are governed by local, nano-scale reactions among adjacent phases along grain boundaries that are driven by local disequilibrium between the solid phases and the grain boundary composition. These reactions modify the grain boundary composition setting up compositional gradients that drive diffusion and change the grain boundary composition elsewhere in the rock, which drive local reactions in these locations. The process may be triggered by the nucleation of a new phase that is out of equilibrium with the existing assemblage and an example is presented based on the transformation of kyanite (Ky) to sillimanite (Sil). Model results reveal that a simple polymorphic transformation (Ky→Sil) can result in local reactions among all phases in the rock and some phases may grow in one locale and be consumed in another. An implication of these results is that interpretation of metamorphic parageneses based on growth or resorption and compositional changes of phases requires careful evaluation of nano-scale processes.

提出了一个模型，其中变质共生是由沿晶界的相邻相之间的局部纳米级反应控制的，这些反应是由固相和晶界成分之间的局部不平衡驱动的。这些反应改变晶界成分，建立成分梯度，驱动扩散并改变岩石中其他地方的晶界成分，从而驱动这些位置的局部反应。该过程可能是由与现有组合不平衡的新相的成核引发的，并且给出了一个基于蓝晶石 (Ky) 到硅线石 (Sil) 转变的示例。模型结果表明，简单的多晶型转变（Ky→Sil）可以导致岩石中所有相之间的局部反应，并且某些相可能在一个区域中生长并在另一个区域中被消耗。这些结果的含义是，基于生长或吸收以及相的组成变化来解释变质共生体需要仔细评估纳米级过程。