石英高压相变研究进展

文中总结了前人有关石英高温高压相变的实验结果。根据以前的实验,在静水压条件下,石英-柯石英-斯石英-CaCl2结构超斯石英相-α-PbO2结构超斯石英相之间的相变方程分别是:p(GPa)=(2.11±0.03)+(9.8×10-4±1.2×10-4)×T(℃),p(GPa)=(8.0±0.2)+(1.1×10-3±3×10-4)×T(℃),p(GPa)=(51±2)+(0.012±0.005)×T(K),p(GPa)=98+(0.0095±0.0016)×T(K)。文中还初步探讨了非静水压状态对石英相变的影响。实验结果表明,差应力的出现降低了石英相变所需要的围压,即相变边界向低压方向偏移,在周永胜等人实验数据的基础上,笔者尝试将二维的相图扩展到三维相图以考虑差应力的影响。最后讨论了石英相变在地学研究中的作用,对比不同的观点分析了前人对超高压变质作用过程的解释,希望可以为以后解释地质资料提供较为广泛的可能性,促进我们对地球内部动力学过程的了解。

Advances in the study of phase transformation of silica under high pressure

The experimental results of phase transformation of silica are reviewed in this paper. Previous experimental results show that phase transformation boundaries between quartz, coesite, stishovite, CaCl2 structure and α-PbO2 structure under hydrostatic pressure condition are p(GPa)=(2.11±0.03)+(9.8×10-4±1.2×10-4)×T(℃), p(GPa)=(8.0±0.2)+(1.1×10-3±3×10-4)×T(℃), p(GPa)=(51±2)+(0.012±0.005)×T(K) and p(GPa)=98+(0.009 5±0.001 6)×T(K), respectively. Furthermore, we discuss the influence of non-hydrostatic pressure on the phase transformation of silica. Existing experimental results show that the confining pressure for phase transformation of silica decreases when differential stress is present. That is, the phase transformation boundary shifts to a lower pressure region under non-hydrostatic pressure conditions. Therefore, we extrapolated the two dimensional phase diagram to a three dimensional one, based on the experimental results of Zhou et al. to include the influence of differential stress on phase transformation of silica. At the end of the paper, the application of experimental results of phase transformation of silica to ultra high pressure metamorphism in the earth interior is discussed. We attempt to provide an alternative explanation of geologic data and thus to improve our understanding of geodynamic processes in earth.