High-pressure behavior of natural single-crystal epidote and clinozoisite up to 40 GPa

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• 作者：Fei Qin ; Xiang Wu ; Ying Wang ; Dawei Fan ; Shan Qin…
• 关键词：Epidote ; Clinozoisite ; Synchrotron single ; crystal X ; ray diffraction ; Compressibility
• 刊名：Physics and Chemistry of Minerals
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：43
• 期：9
• 页码：649-659
• 全文大小：1,234 KB
• 刊物类别：Earth and Environmental Science
• 刊物主题：Earth sciences
  Mineralogy
  Crystallography
  Geochemistry
  Mineral Resources
  
• 出版者：Springer Berlin / Heidelberg
• ISSN：1432-2021
• 卷排序：43

文摘

The comparative compressibility and high-pressure stability of a natural epidote (0.79 Fe-total per formula unit, Fe_tot pfu) and clinozoisite (0.40 Fe_tot pfu) were investigated by single-crystal X-ray diffraction and Raman spectroscopy. The lattice parameters of both phases exhibit continuous compression behavior up to 30 GPa without evidence of phase transformation. Pressure–volume data for both phases were fitted to a third-order Birch–Murnaghan equation of state with V₀ = 461.1(1) Å3, K₀ = 115(2) GPa, and \(K_{0}^{'}\) = 3.7(2) for epidote and V₀ = 457.8(1) Å3, K₀ = 142(3) GPa, and \(K_{0}^{'}\) = 5.2(4) for clinozoisite. In both epidote and clinozoisite, the b-axis is the stiffest direction, and the ratios of axial compressibility are 1.19:1.00:1.15 for epidote and 1.82:1.00:1.19 for clinozoisite. Whereas the compressibility of the a-axis is nearly the same for both phases, the b- and c-axes of the epidote are about 1.5 times more compressible than in clinozoisite, consistent with epidote having a lower bulk modulus. Raman spectra collected up to 40.4 GPa also show no indication of phase transformation and were used to obtain mode Grüneisen parameters (γ_i) for Si–O vibrations, which were found to be 0.5–0.8, typical for hydrous silicate minerals. The average pressure coefficient of Raman frequency shifts for M–O modes in epidote, 2.61(6) cm−1/GPa, is larger than found for clinozoisite, 2.40(6) cm−1/GPa, mainly due to the different compressibility of FeO₆ and AlO₆ octahedra in M3 sites. Epidote and clinozoisite contain about 2 wt% H₂O are thus potentially important carriers of water in subducted slabs.