“Pressure solution” creep: Some causes and mechanisms
“Pressure solution” creep: Some causes and mechanisms
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“压力解决方案”蠕变：一些原因和机制
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发表时间：
1984
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通讯作者：
H. Green
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文献类型：
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作者：
H. Green
尽管有广泛的证据表明，应力控制的溶解和沉淀成岩蚀变和低级变质岩，大量的争议仍然涉及的驱动力和运输机制。为了澄清各种驱动力，自由焓方程在这里扩展，以允许识别不同的条款有助于整体现象。有人认为，在成岩条件下，应力集中在颗粒与颗粒接触将是最大的化学势梯度的来源，并在埋藏和胶结这些不均匀性下降和定向依赖的正应力在准均匀应力场变得重要。这些机制在这些相对冷的、富含H2O的条件下足够有效地操作，使得应力可以保持在晶体塑性变形的阈值以下。晶界上的水至少提供了高扩散率路径，并且在大体积损失的情况下还必须直接通过流体流动做出贡献。大多数关于这种现象的实验工作并没有仔细区分应力增强的溶解度和由于塑性变形或微裂纹引起的溶解度增强。对Sprunt和努尔的某些实验结果的新的热力学分析表明，至少在他们的某些实验中，真压溶液蠕变已经被激活。一个相关的现象，体积转移蠕变相变过程中，涉及显着的体积变化，显示了许多压力解决的特点。
Despite the widespread evidence of stress-controlled dissolution and precipitation in diagenetically altered and low-grade metamorphic rocks, a great deal of controversy remains concerning the driving forces and transport mechanisms involved. To clarify the various driving forces, the free enthalpy equation is expanded here to allow identification of different terms contributing to the overall phenomenon. It is argued that under diagenetic conditions, stress concentrations at grain-to-grain contacts will be the largest source of chemical potential gradients and that upon burial and cementation these inhomogeneities decline and the orientation dependence of normal stress in a quasi-homogeneous stress field becomes important as well. These mechanisms operate efficiently enough under these relatively cold, H2O-rich conditions that stresses can remain below the threshold for crystal plastic deformation. Water on grain boundaries provides at the very least a high diffusivity path and in cases of large volume losses must also contribute directly through fluid flow. Most experimental work on this phenomenon has not distinguished carefully between stress-enhanced solubility and solubility enhancement due to plastic deformation or microcracking. A new thermodynamic analysis of the results of some experiments by Sprunt and Nur suggests that in at least some of their experiments, true pressure solution creep has been activated. A related phenomenon, volume transfer creep during phase transformations which involve significant volume change, displays many of the characteristics of pressure solution.