Quantifying the Effects of Non‐Hydrostatic Stress on Single‐Component Polymorphs
Quantifying the Effects of Non‐Hydrostatic Stress on Single‐Component Polymorphs
复制标题
量化非静水应力对单组分多晶型物的影响
DOI：
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
J. Ague
中科院分区：
文献类型：
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作者：
Benjamin L. Hess;J. Ague
吉布斯自由能是用于计算地质系统中平衡矿物组合的基本热力学势，不适用于非静水应力固体。因此，关于非静水应力在岩石学和地球物理过程中的重要性存在争议。为了帮助解决这一争论，我们考虑了非静水应力对蓝晶石/硅线石、石墨/金刚石、方解石/霰石和石英/柯石英多晶型物对的影响。虽然这些多晶型物与变质过程最相关，但所开发的概念适用于任何单组分固体反应。我们定量地展示了垂直于界面的应力变化如何比平行于界面的应力变化改变多晶型对的平衡温度大约两个数量级。因此，正向应力将多晶型稳定性控制为一级。预计高压多晶型物优先垂直于最大应力成核并平行生长，而低压多晶型物则优先于最小应力。尽管如此，平行于界面的应力变化带来了令人惊讶的可能性，即随着应力的降低，高压多晶型物相对于低压多晶型物变得更加稳定。在具有相互连接的、充满流体的孔隙度的系统中不太可能观察到非静水应力对矿物平衡的影响，因为流体介导的反应在大约恒定的压力下产生矿物组合。然而，在干系统中，反应可以直接发生在弹性固体之间，从而促进非流体静力学热力学的直接应用。非静水应力可能对变质系统的演化很重要，因为多晶型反应的优先方向可以产生地震活动，并可能影响孔隙度和地震各向异性等基本岩石特性。
Gibbs free energy, the fundamental thermodynamic potential used to calculate equilibrium mineral assemblages in geological systems, does not apply to non‐hydrostatically stressed solids. Consequently, there is debate over the significance of non‐hydrostatic stress in petrological and geophysical processes. To help resolve this debate, we consider the effects of non‐hydrostatic stress on the polymorph pairs kyanite/sillimanite, graphite/diamond, calcite/aragonite, and quartz/coesite. While these polymorphs are most relevant to metamorphic processes, the concepts developed are applicable to any single‐component solid reaction. We quantitatively show how stress variations normal to an interface alter equilibrium temperatures of polymorph pairs by approximately two orders of magnitude more than stress variations parallel to an interface. Thus, normal stress controls polymorph stability to first order. High‐pressure polymorphs are expected to preferentially nucleate normal to and grow parallel to the maximum stress and low‐pressure polymorphs, the minimum stress. Nonetheless, stress variations parallel to an interface allow for the surprising possibility that a high‐pressure polymorph can become more stable relative to a low‐pressure polymorph as stress decreases. The effects of non‐hydrostatic stress on mineral equilibrium are unlikely to be observed in systems with interconnected, fluid‐filled porosity, as fluid‐mediated reactions yield mineral assemblages at approximately constant pressures. In dry systems, however, reactions can occur directly between elastic solids, facilitating the direct application of non‐hydrostatic thermodynamics. Non‐hydrostatic stress is likely to be important to the evolution of metamorphic systems, as preferential orientations of polymorphic reactions can generate seismicity and may influence fundamental rock properties such as porosity and seismic anisotropy.
地球中压力和化学过程相互作用的统一基础：来自不同实验的支持
影响因子：
3.5
作者：
Wheeler J
通讯作者：
Wheeler J
影响因子：
16.6
作者：
Stewart EM;Ague JJ
通讯作者：
Ague JJ
压力对地球反应的影响：有时相当恶劣，通常正常，总是重要
影响因子：
3.4
作者：
Wheeler J
通讯作者：
Wheeler J