Raman spectroscopic constraints on compression and metastability of the amphibole tremolite at high pressures and temperatures
Raman spectroscopic constraints on compression and metastability of the amphibole tremolite at high pressures and temperatures
复制标题
高压高温下角闪石透闪石压缩和亚稳定性的拉曼光谱约束
DOI：
10.1007/s00269-020-01095-6
复制
发表时间：
2020
影响因子：
1.4
通讯作者：
Q. Williams
中科院分区：
文献类型：
--
作者：
J. Ott;Q. Williams
角闪石含有高达 2 wt% 的羟基单元形式的水，对水输送到俯冲带的深层岩石圈和上地幔做出了重大贡献，其中脱水反应使水可用于交代过程和上覆地幔楔的通量熔化。在这里，我们研究了钙端元角闪石 Ca 2 Mg 5 Si 8 O 22 (OH) 2 -透闪石的高压和高温行为。透闪石在室温下约 49 GPa 的压力和环境压力下高达 540 K 的温度下通过拉曼光谱进行表征。羟基伸缩振动的行为与之前的红外光谱结果一致，表明达维多夫分裂在该角闪石中的作用很小，并且压力下羟基峰的单调增加模移表明没有接近氢键对称化。与一系列其他含羟基矿物一样，羟基振动具有轻微的负压引起的模式转变。涉及 Ca-O 位移的拉曼峰强度趋势表明钙阳离子键合环境的变化高于 10 GPa。 18 个模式的峰移用于确定其等温和等压模式-Grüneisen 参数（γ iT 和 γ iP ）。根据 Grüneisen 参数计算得出的本征模式非谐性表明，很大程度上是准谐波内模振动，而与阳离子相关的低频振动则显示出显着的非谐性。透闪石结构的一般拓扑结构在 ~ 50 GPa 的范围内保持亚稳定，我们的工作为俯冲带和上地幔中角闪石的亚稳定性以及单斜角闪石结构的固有晶体稳定性提供了约束。
Amphiboles, containing up to 2 wt% water in the form of hydroxyl units, contribute significantly to water transport into the deep lithosphere and upper mantle in subduction zones, where dehydration reactions make the water available for metasomatic processes and flux melting of the overlying mantle wedge. Here, we investigate the high-pressure and temperature behavior of the calcic end-member amphibole Ca 2 Mg 5 Si 8 O 22 (OH) 2 -tremolite. Tremolite is characterized by Raman spectroscopy at pressures to ~ 49 GPa at room temperature, and at temperatures up to 540 K at ambient pressure. The behavior of the hydroxyl stretching vibration, concordant with previous infrared spectroscopic results, implies that the role of Davydov splitting in this amphibole is small, and the monotonically increasing mode shift of the hydroxyl peak under pressure indicates no approach toward hydrogen-bond symmetrization. As with a range of other hydroxyl-bearing minerals, the hydroxyl librations have slightly negative pressure-induced mode shifts. Intensity trends of Raman peaks that involve Ca–O displacements suggest changes in the calcium cation bonding environment above 10 GPa. The peak shifts of 18 modes are used to determine their isothermal and isobaric mode-Grüneisen parameters (γ iT and γ iP ). The intrinsic mode anharmonicities, calculated from the Grüneisen parameters, indicate largely quasi-harmonic internal mode vibrations while the lower frequency vibrations associated with cations display significant anharmonicity. The general topology of the tremolite structure remains metastable to ~ 50 GPa, and our work provides constraints on the metastability of amphiboles in subduction zones and the upper mantle, as well as the intrinsic crystallographic stability of the monoclinic amphibole structure.