Reaction rim growth experiments provide insight into mass transport phenomena, which are important for metamorphic rock-forming processes and deformation mechanisms. We investigated the formation of enstatite single rims between quartz and forsterite and of enstatite-forsterite double rims between quartz and periclase using porous polycrystalline starting materials. About 3 wt% water was added, acting as a catalyst for reactions. Experiments of mainly 4 and 23 h duration were performed in a Paterson-type deformation apparatus at 1000 °C temperature, 400 MPa confining pressure and differential stresses between 0 and 46 MPa. The resulting reaction rim width varied between <1 μm and ≈ 23 μm, depending on duration and type of reaction product. At isostatic pressure conditions, our data indicate that rim growth is proportional to time, controlled by dissolution-precipitation at interfaces of interconnected fluid-filled pores. In contrast, under non-isostatic stress conditions the reaction rim thickness increases non-linearly with time, implying diffusion-controlled growth. The magnitude of differential stress has no systematic influence on the reaction rate. Microstructural observations suggest that deformation-induced reduction of interconnected porosity causes this change in rate-controlling mechanism. For a natural MgO-SiO2 system, the results infer that fast interface-controlled reaction in the presence of high amounts of water is easily suppressed by concurrent deformation.

中文翻译：

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不同应力对湿顽火石和顽火石-镁橄榄石反应边缘生长的影响

反应边缘生长实验提供了对质量传输现象的深入了解，这对变质岩形成过程和变形机制很重要。我们使用多孔多晶起始材料研究了石英和镁橄榄石之间顽火石单边以及石英和方镁石之间顽火石-镁橄榄石双边的形成。添加约 3 wt% 的水，作为反应的催化剂。在 1000 °C 温度、400 MPa 围压和 0 至 46 MPa 之间的差应力下，在 Paterson 型变形装置中进行了主要持续 4 小时和 23 小时的实验。所得反应边缘宽度在 <1 μm 和 ≈ 23 μm 之间变化，具体取决于反应产物的持续时间和类型。在等静压条件下，我们的数据表明边缘增长与时间成正比，由相互连接的充满流体的孔隙界面处的溶解-沉淀控制。相比之下，在非均衡应力条件下，反应边缘厚度随时间非线性增加，这意味着扩散控制增长。不同应力的大小对反应速率没有系统性影响。微观结构观察表明，变形引起的互连孔隙率减少导致了速率控制机制的这种变化。对于天然的 MgO-SiO2 系统，结果推断在大量水存在下的快速界面控制反应很容易被并发变形抑制。意味着扩散控制的增长。不同应力的大小对反应速率没有系统性影响。微观结构观察表明，变形引起的互连孔隙率减少导致了速率控制机制的这种变化。对于天然的 MgO-SiO2 系统，结果推断在大量水存在下的快速界面控制反应很容易被并发变形抑制。意味着扩散控制的增长。不同应力的大小对反应速率没有系统性影响。微观结构观察表明，变形引起的互连孔隙率减少导致了速率控制机制的这种变化。对于天然的 MgO-SiO2 系统，结果推断在大量水存在下的快速界面控制反应很容易被并发变形抑制。