Elastic properties of hydrous ringwoodite (γ-phase) in Mg2SiO4
Elastic properties of hydrous ringwoodite (γ-phase) in Mg2SiO4
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DOI：
10.1016/s0012-821x(98)00077-6
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发表时间：
1998-07-01
影响因子：
5.3
通讯作者：
Parise, JB
中科院分区：
文献类型：
--
作者：
Inoue, T;Weidner, DJ;Parise, JB
本文报道了在19 Gpa和1300℃下合成的含水环木石的单晶弹性性质。EPMA测得镁硅比接近1.95，略低于理想的无水环木石。SIMS测定的H2O含量约为2.2wt%，化学计量比为Mg1.89Si0.97O4H0.33。用X射线衍射法和布里渊散射法测定了单晶的晶格参数(a=8.0786+/-4埃)和弹性常数。晶体结构为立方Fd3m，其晶胞体积比无水环木的晶胞体积大0.51%。含水环木的绝热单晶弹性模数分别为：C-11=281+/-6，C-44=117+/-4，C-12=92+/-5，各向同性系数K-VRH=155+/-4，G(VRH)=107+/-3，分别比无水环木小16%和10%。因此，与无水环木相比，如果存在含水环木，地幔过渡带的地震速度会大大降低。此外，我们的结果还表明，相对于无水环木石，各向异性得到了增强。利用这些结果，我们讨论了湿地幔过渡带中520公里的地震不连续性。(C)1998 Elsevier Science B.V.保留所有权利。
Single-crystal elastic properties of hydrous ringwoodite are reported for samples that were synthesized at 19 GPa and 1300 degrees C. The Mg/Si ratio is determined to be similar to 1.95 by EPMA, which is slightly lower than that of ideal anhydrous ringwoodite. The H2O content determined by SIMS is similar to 2.2 wt%, resulting in the stoichiometry Mg1.89Si0.97O4H0.33.The lattice parameter (a = 8.0786 +/- 4 Angstrom) and elastic constants were determined from a single crystal with X-ray diffractometry and Brillouin scattering spectroscopy. The crystal structure is cubic Fd3m, with a unit cell volume which is 0.51% larger than that of the anhydrous ringwoodite. The adiabatic single-crystal elastic moduli of hydrous ringwoodite, in GPa, are: C-11 = 281 +/- 6, C-44 = 117 +/- 4, C-12 = 92 +/- 5. The isotropic properties of hydrous ringwoodite are K-VRH = 155 +/- 4 and G(VRH) = 107 +/- 3 which are about 16 and 10% smaller than those of anhydrous ringwoodite. Thus hydrous ringwoodite, if present, drastically reduces the seismic velocity in the mantle transition zone relative to anhydrous ringwoodite. In addition, our results show that the anisotropy is enhanced relative to anhydrous ringwoodite. Using the present results, we discuss the 520 km seismic discontinuity in a wet mantle transition zone. (C) 1998 Elsevier Science B.V. All rights reserved.