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Title: Isosymmetric pressure-induced bonding increase changes compression behavior of clinopyroxenes across jadeite-aegirine solid solution in subduction zones

Abstract

Pyroxenes are among the most important minerals of Earth's crust and upper mantle and play significant role in controlling subduction at convergent margins. In this study, synchrotron-based single-crystal X-ray diffraction experiments were carried out on a natural aegirine [NaFe 3+Si 2O 6] sample at ambient temperature and high pressures to 60 GPa, simulating conditions within the coldest part of a subduction zone consisting of old lithosphere. The diffraction data reveal no obvious sign of structural phase transition in aegirine within this pressure range; however, several relevant structural parameter trends change noticeably at approximately 24 GPa, indicating the presence of the previously predicted isosymmetric bonding change, related to increase of coordination number of Na + at M2 site. The pressure-volume data, fit with third-order Birch-Murnaghan (BM3) equation of state over the whole pressure range, yields K T0 = 126(2) GPa and K' T0 = 3.3(1), while separate BM3 fits performed for the 0–24.0 GPa and 29.9–60.4 GPa pressure ranges give K T0 = 118(3) GPa, K' T0 = 4.2(3) and K T0 = 133(2) GPa, K' T0 = 3.0(1), suggesting that the structure stiffens as a result of the new bond formation. Aegirine exhibits strong anisotropic compression with unit strain axialmore » ratios ε 123 = 1.00:2.44:1.64. Structural refinements reveal that NaO 8 polyhedron is the most compressible and SiO 4 tetrahedron has the lowest compressibility. Lastly, the consequence of bonding transition is that the compressional behavior of aegirine below ~24 GPa and above that pressure is quite different, with likely consequences for relevant thermodynamic parameters and ion diffusion coefficients.« less

Authors:
 [1]; ORCiD logo [2];  [3];  [4]; ORCiD logo [2]; ORCiD logo [2]
  1. Chinese Academy of Sciences, Guiyang (China); Univ. of Hawai'i at Mānoa, Honolulu HI (United States); Univ. of Chinese Academy of Sciences, Beijing (China)
  2. Univ. of Hawai'i at Mānoa, Honolulu HI (United States)
  3. Chinese Academy of Sciences, Guiyang (China)
  4. Univ. of Arizona, Tucson, AZ (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
OSTI Identifier:
1355027
Grant/Contract Number:  
FG02-94ER14466; AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Solid Earth
Additional Journal Information:
Journal Volume: 122; Journal Issue: 1; Journal ID: ISSN 2169-9313
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
ENGLISH
Subject:
58 GEOSCIENCES; pyroxenes; high pressure; synchrotron single‐crystal X‐ray diffraction; bonding transition; mantle; subduction zone

Citation Formats

Xu, Jingui, Zhang, Dongzhou, Fan, Dawei, Downs, Robert T., Hu, Yi, and Dera, Przemyslaw K. Isosymmetric pressure-induced bonding increase changes compression behavior of clinopyroxenes across jadeite-aegirine solid solution in subduction zones. United States: N. p., 2016. Web. doi:10.1002/2016JB013502.
Xu, Jingui, Zhang, Dongzhou, Fan, Dawei, Downs, Robert T., Hu, Yi, & Dera, Przemyslaw K. Isosymmetric pressure-induced bonding increase changes compression behavior of clinopyroxenes across jadeite-aegirine solid solution in subduction zones. United States. doi:10.1002/2016JB013502.
Xu, Jingui, Zhang, Dongzhou, Fan, Dawei, Downs, Robert T., Hu, Yi, and Dera, Przemyslaw K. Wed . "Isosymmetric pressure-induced bonding increase changes compression behavior of clinopyroxenes across jadeite-aegirine solid solution in subduction zones". United States. doi:10.1002/2016JB013502. https://www.osti.gov/servlets/purl/1355027.
@article{osti_1355027,
title = {Isosymmetric pressure-induced bonding increase changes compression behavior of clinopyroxenes across jadeite-aegirine solid solution in subduction zones},
author = {Xu, Jingui and Zhang, Dongzhou and Fan, Dawei and Downs, Robert T. and Hu, Yi and Dera, Przemyslaw K.},
abstractNote = {Pyroxenes are among the most important minerals of Earth's crust and upper mantle and play significant role in controlling subduction at convergent margins. In this study, synchrotron-based single-crystal X-ray diffraction experiments were carried out on a natural aegirine [NaFe3+Si2O6] sample at ambient temperature and high pressures to 60 GPa, simulating conditions within the coldest part of a subduction zone consisting of old lithosphere. The diffraction data reveal no obvious sign of structural phase transition in aegirine within this pressure range; however, several relevant structural parameter trends change noticeably at approximately 24 GPa, indicating the presence of the previously predicted isosymmetric bonding change, related to increase of coordination number of Na+ at M2 site. The pressure-volume data, fit with third-order Birch-Murnaghan (BM3) equation of state over the whole pressure range, yields KT0 = 126(2) GPa and K'T0 = 3.3(1), while separate BM3 fits performed for the 0–24.0 GPa and 29.9–60.4 GPa pressure ranges give KT0 = 118(3) GPa, K'T0 = 4.2(3) and KT0 = 133(2) GPa, K'T0 = 3.0(1), suggesting that the structure stiffens as a result of the new bond formation. Aegirine exhibits strong anisotropic compression with unit strain axial ratios ε1:ε2:ε3 = 1.00:2.44:1.64. Structural refinements reveal that NaO8 polyhedron is the most compressible and SiO4 tetrahedron has the lowest compressibility. Lastly, the consequence of bonding transition is that the compressional behavior of aegirine below ~24 GPa and above that pressure is quite different, with likely consequences for relevant thermodynamic parameters and ion diffusion coefficients.},
doi = {10.1002/2016JB013502},
journal = {Journal of Geophysical Research. Solid Earth},
number = 1,
volume = 122,
place = {United States},
year = {Wed Nov 23 00:00:00 EST 2016},
month = {Wed Nov 23 00:00:00 EST 2016}
}

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