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Title: Compressibility and thermal expansion of hydrous ringwoodite with 2.5(3) wt% H[subscript 2]O

Abstract

Ringwoodite ({gamma}-Mg{sub 2}SiO{sub 4}) is the stable polymorph of olivine in the transition zone between 525-660 km depth, and can incorporate weight percent amounts of H{sub 2}O as hydroxyl, with charge compensated mainly by Mg vacancies (Mg{sup 2+} = 2H{sup +}), but also possibly as (Si{sup 4+} = 4H{sup +} and Mg{sup 2+} + 2H{sup +} = Si{sup 4+}). We synthesized pure Mg ringwoodite containing 2.5(3) wt% H{sub 2}O, measured by secondary ion mass spectrometry (SIMS), and determined its compressibility at 300 K by single-crystal and powder X-ray diffraction (XRD), as well as its thermal expansion behavior between 140 and 740 K at room pressure. A third-order Birch-Murnaghan equation of state (BM3 EOS) fits values of the isothermal bulk modulus K{sub T0} = 159(7) GPa and (dK{sub T}/dP){sub P = 0} = K' = 6.7(7) for single-crystal XRD; K{sub T0} = 161(4) GPa and K' = 5.4(6) for powder XRD, with K{sub T0} = 160(2) GPa and K' = 6.2(3) for the combined data sets. At room pressure, hydrous ringwoodite breaks down by an irreversible unit-cell expansion above 586 K, which may be related to dehydration and changes in the disorder mechanisms. Single-crystal intensity data were collected at various temperaturesmore » up to 736 K, and show that the cell volume V(cell) has a mean thermal expansion coefficient {alpha}{sub V0} of 40(4) x 10{sup -6}/K (143-736 K), and 29(2) x 10{sup -6}/K (143-586 K before irreversible expansion). V(Mg) have {alpha}{sub 0} values of 41(3) x 10{sup -6}/K (143-736 K), and V(Si) has {alpha}{sub 0} values of 20(3) x 10{sup -6}/K (143-586 K) and 132(4) x 10{sup -6}K (586-736 K). Based on the experimental data and previous work from {sup 29}Si NMR, we propose that during the irreversible expansion, a small amount of H{sup +} cations in Mg sites transfer to Si sites without changing the cubic spinel structure of ringwoodite, and the substituted Si{sup 4+} cations move to the normally vacant octahedral site at (1/2, 1/2, 0). Including new SIMS data on this and several Mg-ringwoodite samples from previous studies, we summarize volume-hydration data and show that the Mg{sup 2+} = 2H{sup +} dominates up to about 2 wt% H{sub 2}O, where a discontinuity in the volume vs. H{sub 2}O content trend suggests that other hydration mechanisms become important at very high H{sub 2}O contents.« less

Authors:
; ; ; ; ; ; ; ; ; ;  [1];  [2];  [2];  [2];  [2];  [2]
  1. (Bayreuth)
  2. (
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
DOE - BASIC ENERGY SCIENCESDOE - OTHERNSFOTHER
OSTI Identifier:
1037479
Resource Type:
Journal Article
Resource Relation:
Journal Name: American Mineralogist; Journal Volume: 97; Journal Issue: (4) ; 04, 2012
Country of Publication:
United States
Language:
ENGLISH

Citation Formats

Ye, Yu, Brown, David A., Smyth, Joseph R., Panero, Wendy R., Jacobsen, Steven D., Chang, Yun-Yuan, Townsend, Joshua P., Thomas, Sylvia-Monique, Hauri, Erik H., Dera, Przemyslaw, Frost, Daniel J., Colorado), CIW), UC), NWU), and OSU). Compressibility and thermal expansion of hydrous ringwoodite with 2.5(3) wt% H[subscript 2]O. United States: N. p., 2016. Web. doi:10.2138/am.2012.4010.
Ye, Yu, Brown, David A., Smyth, Joseph R., Panero, Wendy R., Jacobsen, Steven D., Chang, Yun-Yuan, Townsend, Joshua P., Thomas, Sylvia-Monique, Hauri, Erik H., Dera, Przemyslaw, Frost, Daniel J., Colorado), CIW), UC), NWU), & OSU). Compressibility and thermal expansion of hydrous ringwoodite with 2.5(3) wt% H[subscript 2]O. United States. doi:10.2138/am.2012.4010.
Ye, Yu, Brown, David A., Smyth, Joseph R., Panero, Wendy R., Jacobsen, Steven D., Chang, Yun-Yuan, Townsend, Joshua P., Thomas, Sylvia-Monique, Hauri, Erik H., Dera, Przemyslaw, Frost, Daniel J., Colorado), CIW), UC), NWU), and OSU). 2016. "Compressibility and thermal expansion of hydrous ringwoodite with 2.5(3) wt% H[subscript 2]O". United States. doi:10.2138/am.2012.4010.
@article{osti_1037479,
title = {Compressibility and thermal expansion of hydrous ringwoodite with 2.5(3) wt% H[subscript 2]O},
author = {Ye, Yu and Brown, David A. and Smyth, Joseph R. and Panero, Wendy R. and Jacobsen, Steven D. and Chang, Yun-Yuan and Townsend, Joshua P. and Thomas, Sylvia-Monique and Hauri, Erik H. and Dera, Przemyslaw and Frost, Daniel J. and Colorado) and CIW) and UC) and NWU) and OSU)},
abstractNote = {Ringwoodite ({gamma}-Mg{sub 2}SiO{sub 4}) is the stable polymorph of olivine in the transition zone between 525-660 km depth, and can incorporate weight percent amounts of H{sub 2}O as hydroxyl, with charge compensated mainly by Mg vacancies (Mg{sup 2+} = 2H{sup +}), but also possibly as (Si{sup 4+} = 4H{sup +} and Mg{sup 2+} + 2H{sup +} = Si{sup 4+}). We synthesized pure Mg ringwoodite containing 2.5(3) wt% H{sub 2}O, measured by secondary ion mass spectrometry (SIMS), and determined its compressibility at 300 K by single-crystal and powder X-ray diffraction (XRD), as well as its thermal expansion behavior between 140 and 740 K at room pressure. A third-order Birch-Murnaghan equation of state (BM3 EOS) fits values of the isothermal bulk modulus K{sub T0} = 159(7) GPa and (dK{sub T}/dP){sub P = 0} = K' = 6.7(7) for single-crystal XRD; K{sub T0} = 161(4) GPa and K' = 5.4(6) for powder XRD, with K{sub T0} = 160(2) GPa and K' = 6.2(3) for the combined data sets. At room pressure, hydrous ringwoodite breaks down by an irreversible unit-cell expansion above 586 K, which may be related to dehydration and changes in the disorder mechanisms. Single-crystal intensity data were collected at various temperatures up to 736 K, and show that the cell volume V(cell) has a mean thermal expansion coefficient {alpha}{sub V0} of 40(4) x 10{sup -6}/K (143-736 K), and 29(2) x 10{sup -6}/K (143-586 K before irreversible expansion). V(Mg) have {alpha}{sub 0} values of 41(3) x 10{sup -6}/K (143-736 K), and V(Si) has {alpha}{sub 0} values of 20(3) x 10{sup -6}/K (143-586 K) and 132(4) x 10{sup -6}K (586-736 K). Based on the experimental data and previous work from {sup 29}Si NMR, we propose that during the irreversible expansion, a small amount of H{sup +} cations in Mg sites transfer to Si sites without changing the cubic spinel structure of ringwoodite, and the substituted Si{sup 4+} cations move to the normally vacant octahedral site at (1/2, 1/2, 0). Including new SIMS data on this and several Mg-ringwoodite samples from previous studies, we summarize volume-hydration data and show that the Mg{sup 2+} = 2H{sup +} dominates up to about 2 wt% H{sub 2}O, where a discontinuity in the volume vs. H{sub 2}O content trend suggests that other hydration mechanisms become important at very high H{sub 2}O contents.},
doi = {10.2138/am.2012.4010},
journal = {American Mineralogist},
number = (4) ; 04, 2012,
volume = 97,
place = {United States},
year = 2016,
month = 7
}
  • Review of recent mineral physics literature shows consistent trends for the influence of Fe and H 2O on the bulk modulus (K0) of wadsleyite and ringwoodite, the major phases of Earth's mantle transition zone (410–660 km). However, there is little consensus on the first pressure derivative, K0' = (dK/dP)P=0, which ranges from about 4 to >5 across experimental studies and compositions. Here we demonstrate the importance of K0' in evaluating the bulk sound velocity of the transition zone in terms of water content and provide new constraints on the effect of H 2O on K0' for wadsleyite and ringwoodite bymore » conducting a comparative compressibility study. In the experiment, multiple crystals of hydrous Fo90 wadsleyite containing 2.0 and 0.25 wt % H 2O were loaded into the same diamond anvil cell, along with hydrous ringwoodite containing 1.4 wt % H 2O. By measuring their pressure-volume evolution simultaneously up to 32 GPa, we constrain the difference in K0' independent of the pressure scale, finding that H 2O has no effect on K0', whereas the effect of H 2O on K0 is significant. The fitted K0' values of hydrous wadsleyite (0.25 and 2.0 wt % H 2O) and hydrous ringwoodite (1.4 wt % H 2O) examined in this study were found to be identical within uncertainty, with K0' ~3.7(2). New secondary-ion mass spectrometry measurements of the H 2O content of these and previously investigated wadsleyite samples shows the bulk modulus of wadsleyite is reduced by 7.0(5) GPa/wt % H 2O, independent of Fe content for upper mantle compositions. Because K0' is unaffected by H 2O, the reduction of bulk sound velocity in very hydrous regions of transition zone is expected to be on the order of 1.6%, which is potentially detectible in high-resolution, regional seismology studies.« less
  • Hydrous wadsleyite ({beta}-Mg{sub 2}SiO{sub 4}) with 2.8 wt% water content has been synthesized at 15 GPa and 1250 C in a multi-anvil press. The unit-cell parameters are: a = 5.6686(8), b = 11.569(1), c = 8.2449(9) {angstrom}, {beta} = 90.14(1){sup o}, and V = 540.7(1) {angstrom}{sup 3}, and the space group is I2/m. The structure was refined in space groups Imma and I2/m. The room-pressure structure differs from that of anhydrous wadsleyite principally in the increased cation distances around O1, the non-silicate oxygen. The compression of a single crystal of this wadsleyite was measured up to 61.3(7) GPa at roommore » temperature in a diamond anvil cell with neon as pressure medium by X-ray diffraction at Sector 13 at the Advanced Photon Source, Argonne National Laboratory. The experimental pressure range was far beyond the wadsleyite-ringwoodite phase-transition pressure at 525 km depth (17.5 GPa), while a third-order Birch-Murnaghan equation of state (EoS) [V{sub 0} = 542.7(8) {angstrom}{sup 3}, K{sub T0} = 137(5) GPa, K{prime} = 4.6(3)] still fits the data well. In comparison, the second-order fit gives V{sub 0} = 542.7(8) {angstrom}{sup 3}, K{sub T} = 147(2) GPa. The relation between isothermal bulk modulus of hydrous wadsleyite K{sub T0} and water content C{sub H{sub 2}O} is: K{sub T0} = 171(1)-12(1) C{sub H{sub 2}O} (up to 2.8 wt% water). The axial-compressibility {beta}{sub c} is larger than both {beta}{sub a} and {beta}{sub b}, consistent with previous studies and analogous to the largest coefficient of thermal expansion along the c-axis.« less