Thermoelastic properties of ice VII and its high-pressure polymorphs: Implications for dynamics of cold slab subduction in the lower mantle
Thermoelastic properties of ice VII and its high-pressure polymorphs: Implications for dynamics of cold slab subduction in the lower mantle
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DOI：
10.1016/j.epsl.2010.09.037
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发表时间：
2010-11
影响因子：
5.3
通讯作者：
Y. Asahara;K. Hirose;Y. Ohishi;N. Hirao;M. Murakami
中科院分区：
文献类型：
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作者：
Y. Asahara;K. Hirose;Y. Ohishi;N. Hirao;M. Murakami
用布里渊散射法测量了室温下6-60GPa压力范围内多晶水冰中的声速。在40-60GPa的压力范围内，同步加速器x射线衍射测量与布里渊散射测量同时进行。得到的高压冰弹性模量表明，bcc结构冰在约40GPa和58GPa时分别经历了与氢键状态变化相关的两次转变，即冰VII在40GPa时向冰VII的过渡前状态转变，以及冰X在58GPa时向动态无序状态转变。这一观察结果与以前的光谱研究和x射线衍射研究一致。根据实测的声速和体积数据，得到了冰VII及其高压多晶体的绝热弹性模量和比热的压力依赖关系。等温压缩数据来自以往的研究。得到了压力与ice VII绝热弹性模量的关系式：Ks=4.0(2)+8.51(4)×P−0.081(2)×P2+5.2(4)×10−4×P3；μs = 14(2) + 1.7(3)×P−0.04(2)×P2 + 5(3)×10−4×P3。得到了冰VII室温比热与压力的经验关系式：Cp=3.3(2)+22.1(1)×e−0.058(2)P。这一结果表明，从冰VII到动态无序冰X的转变伴随着冰的一些热力学性质的不连续变化。冰VII与动力无序冰X之间的弹性差异可能会影响地球下地幔冷俯冲板块和冰行星内部的动力学。本研究获得的冰高压多晶的热弹性特性有助于阐明地球和冰态行星及卫星的动力学和演化。
Acoustic velocities in polycrystalline H2O ice have been measured at room temperature in a pressure range 6–60GPa by a Brillouin scattering method. Synchrotron X-ray diffraction measurements were also conducted simultaneously with the Brillouin scattering measurements in a pressure range 40–60GPa. The obtained elastic moduli of high-pressure ice indicate that bcc-structured ice undergoes two transitions related to a change in the hydrogen bonding state at approximately 40GPa and 58GPa, i.e. transitions of ice VII to the pre-transitional state of ice VII at 40GPa and to the dynamically disordered ice X at 58GPa, respectively. This observation is consistent with previous spectroscopic studies and X-ray diffraction studies. Pressure dependencies of adiabatic elastic moduli and specific heat for ice VII and its high-pressure polymorphs were obtained from the acoustic velocity and volume data measured in this study. Isothermal compression data were obtained from previous studies. The relationships between pressure and adiabatic elastic moduli for ice VII were obtained as follows: Ks=4.0(2)+8.51(4)×P−0.081(2)×P2+5.2(4)×10−4×P3; μs=14(2)+1.7(3)×P−0.04(2)×P2+5(3)×10−4×P3. An empirical relationship between specific heat and pressure at room temperature was obtained for ice VII as follows: Cp=3.3(2)+22.1(1)×e−0.058(2)P. This result implies that the transition from ice VII to the dynamically disordered ice X is accompanied with a discontinuous change in several thermodynamic properties of ice. The elasticity difference between ice VII and the dynamically disordered ice X may affect the dynamics of cold subducting slabs in Earth's lower mantle and the interiors of icy planets. The thermoelastic properties of high-pressure polymorphs of ice obtained in this study could contribute to clarifying the dynamics and the evolution of Earth and icy planets and satellites.